hypothesis plant growth sunlight

Suggestions or feedback?

MIT News | Massachusetts Institute of Technology

• Machine learning
• Social justice
• Black holes
• Classes and programs

Departments

• Aeronautics and Astronautics
• Brain and Cognitive Sciences
• Architecture
• Political Science
• Mechanical Engineering

Centers, Labs, & Programs

• Abdul Latif Jameel Poverty Action Lab (J-PAL)
• Picower Institute for Learning and Memory
• Lincoln Laboratory
• School of Architecture + Planning
• School of Engineering
• School of Humanities, Arts, and Social Sciences
• Sloan School of Management
• School of Science
• MIT Schwarzman College of Computing

Understanding how plants use sunlight

Press contact :.

Previous image Next image

Plants rely on the energy in sunlight to produce the nutrients they need. But sometimes they absorb more energy than they can use, and that excess can damage critical proteins. To protect themselves, they convert the excess energy into heat and send it back out. Under some conditions, they may reject as much as 70 percent of all the solar energy they absorb.

“If plants didn’t waste so much of the sun’s energy unnecessarily, they could be producing more biomass,” says  Gabriela S. Schlau-Cohen , the Cabot Career Development Assistant Professor of Chemistry. Indeed, scientists estimate that algae could grow as much as 30 percent more material for use as biofuel. More importantly, the world could increase crop yields — a change needed to prevent the significant shortfall between agricultural output and demand for food expected by 2050.

The challenge has been to figure out exactly how the photoprotection system in plants works at the molecular level, in the first 250 picoseconds of the photosynthesis process. (A picosecond is a trillionth of a second.)

“If we could understand how absorbed energy is converted to heat, we might be able to rewire that process to optimize the overall production of biomass and crops,” says Schlau-Cohen. “We could control that switch to make plants less hesitant to shut off the protection. They could still be protected to some extent, and even if a few individuals died, there’d be an increase in the productivity of the remaining population.”

First steps of photosynthesis

Critical to the first steps of photosynthesis are proteins called light-harvesting complexes, or LHCs. When sunlight strikes a leaf, each photon (particle of light) delivers energy that excites an LHC. That excitation passes from one LHC to another until it reaches a so-called reaction center, where it drives chemical reactions that split water into oxygen gas, which is released, and positively charged particles called protons, which remain. The protons activate the production of an enzyme that drives the formation of energy-rich carbohydrates needed to fuel the plant’s metabolism.

But in bright sunlight, protons may form more quickly than the enzyme can use them, and the accumulating protons signal that excess energy is being absorbed and may damage critical components of the plant’s molecular machinery. So some plants have a special type of LHC — called a light-harvesting complex stress-related, or LHCSR — whose job is to intervene. If proton buildup indicates that too much sunlight is being harvested, the LHCSR flips the switch, and some of the energy is dissipated as heat.

It’s a highly effective form of sunscreen for plants — but the LHCSR is reluctant to switch off that quenching setting. When the sun is shining brightly, the LHCSR has quenching turned on. When a passing cloud or flock of birds blocks the sun, it could switch it off and soak up all the available sunlight. But instead, the LHCSR leaves it on — just in case the sun suddenly comes back. As a result, plants reject a lot of energy that they could be using to build more plant material.

An evolutionary success

Much research has focused on the quenching mechanism that regulates the flow of energy within a leaf to prevent damage. Optimized by 3.5 billion years of evolution, its capabilities are impressive. First, it can deal with wildly varying energy inputs. In a single day, the sun’s intensity can increase and decrease by a factor of 100 or even 1,000. And it can react to changes that occur slowly over time — say, at sunrise — and those that happen in just seconds, for example, due to a passing cloud.

Researchers agree that one key to quenching is a pigment within the LHCSR — called a carotenoid — that can take two forms: violaxanthin (Vio) and zeaxanthin (Zea). They’ve observed that LHCSR samples are dominated by Vio molecules under low-light conditions and Zea molecules under high-light conditions. Conversion from Vio to Zea would change various electronic properties of the carotenoids, which could explain the activation of quenching. However, it doesn’t happen quickly enough to respond to a passing cloud. That type of fast change could be a direct response to the buildup of protons, which causes a difference in pH from one region of the LHCSR to another.

Clarifying those photoprotection mechanisms experimentally has proved difficult. Examining the behavior of samples containing thousands of proteins doesn’t provide insights into the molecular-level behavior because various quenching mechanisms occur simultaneously and on different time scales — and in some cases, so quickly that they’re difficult or impossible to observe experimentally.

Testing the behavior of proteins one at a time

Schlau-Cohen and her MIT chemistry colleagues, postdoc Toru Kondo and graduate student Wei Jia Chen, decided to take another tack. Focusing on the LHCSR found in green algae and moss, they examined what was different about the way that stress-related proteins rich in Vio and those rich in Zea respond to light — and they did it one protein at a time.

According to Schlau-Cohen, their approach was made possible by the work of her collaborator Roberto Bassi and his colleagues Alberta Pinnola and Luca Dall’Osto at the University of Verona, in Italy. In earlier research, they had figured out how to purify the individual proteins known to play key roles in quenching. They thus were able to provide samples of individual LHCSRs, some enriched with Vio carotenoids and some with Zea carotenoids.

To test the response to light exposure, Schlau-Cohen’s team uses a laser to shine picosecond light pulses onto a single LHCSR. Using a highly sensitive microscope, they can then detect the fluorescence emitted in response. If the LHCSR is in quench-on mode, it will turn much of the incoming energy into heat and expel it. Little or no energy will be left to be reemitted as fluorescence. But if the LHCSR is in quench-off mode, all of the incoming light will come out as fluorescence.

“So we’re not measuring the quenching directly,” says Schlau-Cohen. “We’re using decreases in fluorescence as a signature of quenching. As the fluorescence goes down, the quenching goes up.”

Using that technique, the MIT researchers examined the two proposed quenching mechanisms: the conversion of Vio to Zea and a direct response to a high proton concentration.

To address the first mechanism, they characterized the response of the Vio-rich and Zea-rich LHCSRs to the pulsed laser light using two measures: the intensity of the fluorescence (based on how many photons they detect in one millisecond) and its lifetime (based on the arrival time of the individual photons).

Using the measured intensities and lifetimes of responses from hundreds of individual LHCSR proteins, they generated the probability distributions shown in the figure above. In each case, the red region shows the most likely outcome based on results from all the single-molecule tests. Outcomes in the yellow region are less likely, and those in the green region are least likely.

The left figure shows the likelihood of intensity-lifetime combinations in the Vio samples, representing the behavior of the quench-off response. Moving to the Zea results in the middle figure, the population shifts to a shorter lifetime and also to a much lower-intensity state — an outcome consistent with Zea being the quench-on state.

To explore the impact of proton concentration, the researchers changed the pH of their system. The results just described came from individual proteins suspended in a solution with a pH of 7.5. In parallel tests, the researchers suspended the proteins in an acidic solution of pH 5, thus in the presence of abundant protons, replicating conditions that would prevail under bright sunlight.

The right figure shows results from the Vio samples. Shifting from pH 7.5 to pH 5 brings a significant decrease in intensity, as it did with the Zea samples, so quenching is now on. But it brings only a slightly shorter lifetime, not the significantly shorter lifetime observed with Zea.

The dramatic decrease in intensity with the Vio-to-Zea conversion and the lowered pH suggests that both are quenching behaviors. But the different impact on lifetime suggests that the quenching mechanisms are different.

“Because the most likely outcome—the red region—moves in different directions, we know that two distinct quenching processes are involved,” says Schlau-Cohen.

Their investigation brought one more interesting observation. The intensity-lifetime results for Vio and Zea in the two pH environments are consistent when they’re taken at time intervals spanning seconds or even minutes in a given sample. According to Schlau-Cohen, the only explanation for such stability is that the responses are due to differing structures, or conformations, of the protein.

“It was known that both pH and the switch of the carotenoid from violaxanthin to zeaxanthin played a role in quenching,” she says. “But what we saw was that there are two different conformational switches at work.”

Based on their results, Schlau-Cohen proposes that the LHCSR can have three distinct conformations. When sunlight is dim, it assumes a conformation that allows all available energy to come in. If bright sunlight suddenly returns, protons quickly build up and reach a critical concentration at which point the LHCSR switches to a quenching-on conformation — probably a more rigid structure that permits energy to be rejected by some mechanism not yet fully understood. And when light increases slowly, the protons accumulate over time, activating an enzyme that in turn accumulates, in the process causing a carotenoid in the LHCSR to change from Vio to Zea — a change in both composition and structure.

“So the former quenching mechanism works in a few seconds, while the latter works over time scales of minutes to hours,” says Schlau-Cohen. Together, those conformational options explain the remarkable control system that enables plants to regulate energy uptake from a source that’s constantly changing.

Exploring what comes next

Schlau-Cohen is now turning her attention to the next important step in photosynthesis — the rapid transfer of energy through the network of LHCs to the reaction center. The structure of individual LHCs has a major impact on how quickly excitation energy can jump from one protein to the next. Some investigators are therefore exploring how the LHC structure may be affected by interactions between the protein and the lipid membrane in which it’s suspended.

However, their experiments typically involve sample proteins mixed with detergent, and while detergent is similar to natural lipids in some ways, its impact on proteins can be very different, says Schlau-Cohen. She and her colleagues have therefore developed a new system that suspends single proteins in lipids more like those found in natural membranes. Already, tests using ultrafast spectroscopy on those samples has shown that one key energy-transfer step occurs 30 percent faster than measured in detergents. Those results support the value of the new technique in exploring photosynthesis and demonstrate the importance of using near-native lipid environments in such studies.

Research on the heat-dissipation mechanism was supported by the Center for Excitonics, an Energy Frontier Research Center funded by the US Department of Energy; a CIFAR Azrieli Global Scholar Award; and the European Economic Community projects AccliPhot and SE2B. Research on energy transfer was supported by the US Department of Energy, Office of Science, Office of Basic Energy, and by the Singapore-MIT Alliance for Research and Technology.

This article appears in the  Autumn 2018  issue of Energy Futures , the magazine of the MIT Energy Initiative.

Share this news article on:

Related links.

• Paper: “Single-molecule spectroscopy of LHCSR1 protein dynamics identifies two distinct states responsible for multi-timescale photosynthetic photoprotection”
• Paper: "Impact of the lipid bilayer on energy transfer kinetics in the photosynthetic protein LH2”
• Gabriela Schlau-Cohen
• Energy Futures Magazine
• MIT Energy Initiative
• Department of Chemistry

Related Topics

• Sustainability
• Biochemistry
• Spectroscopy

Related Articles

Harnessing the right amount of sunshine

Synthetic circuits can harvest light energy

How photosynthetic pigments harvest light

Secret of efficient photosynthesis is decoded

Previous item Next item

More MIT News

Understanding why autism symptoms sometimes improve amid fever

Read full story →

School of Engineering welcomes new faculty

Study explains why the brain can robustly recognize images, even without color

Turning up the heat on next-generation semiconductors

Sarah Millholland receives 2024 Vera Rubin Early Career Award

A community collaboration for progress

• More news on MIT News homepage →

Massachusetts Institute of Technology 77 Massachusetts Avenue, Cambridge, MA, USA

• Map (opens in new window)
• Events (opens in new window)
• People (opens in new window)
• Careers (opens in new window)
• Accessibility
• Social Media Hub
• MIT on Facebook
• MIT on YouTube
• MIT on Instagram

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Front Plant Sci

Plant Growth under Natural Light Conditions Provides Highly Flexible Short-Term Acclimation Properties toward High Light Stress

Tobias schumann.

1 Plant Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany

2 Department of Plant Physiology, Umeå University, Umeå, Sweden

Michael Melzer

3 Physiology and Cell Biology, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Seeland, Germany

Peter Dörmann

4 Molecular Biotechnology/Biochemistry, Institute of Molecular Physiology and Biotechnology of Plants (IMBIO), Rheinische Friedrich-Wilhelms-University Bonn, Bonn, Germany

Peter Jahns

Associated data.

Efficient acclimation to different growth light intensities is essential for plant fitness. So far, most studies on light acclimation have been conducted with plants grown under different constant light regimes, but more recent work indicated that acclimation to fluctuating light or field conditions may result in different physiological properties of plants. Thale cress ( Arabidopsis thaliana ) was grown under three different constant light intensities (LL: 25 μmol photons m −2 s −1 ; NL: 100 μmol photons m −2 s − 1 ; HL: 500 μmol photons m −2 s −1 ) and under natural fluctuating light (NatL) conditions. We performed a thorough characterization of the morphological, physiological, and biochemical properties focusing on photo-protective mechanisms. Our analyses corroborated the known properties of LL, NL, and HL plants. NatL plants, however, were found to combine characteristics of both LL and HL grown plants, leading to efficient and unique light utilization capacities. Strikingly, the high energy dissipation capacity of NatL plants correlated with increased dynamics of thylakoid membrane reorganization upon short-term acclimation to excess light. We conclude that the thylakoid membrane organization and particularly the light-dependent and reversible unstacking of grana membranes likely represent key factors that provide the basis for the high acclimation capacity of NatL grown plants to rapidly changing light intensities.

Introduction

Efficient acclimation to changing environmental conditions is a prerequisite for the survival and competitiveness of plants in the field. Proper acclimation to the light availability at a given habitat is essential to allow for efficient light utilization under light-limiting conditions and to avoid photo-oxidative damage under excess-light condition. Long-term acclimation to either low light (LL) or high light (HL) conditions occurs in the time range of days to months and involves—among others—adjustments of leaf architecture, chloroplast structure, composition of the photosynthetic electron transport chain, and regulation of photosynthetic light utilization (Boardman, 1977 ; Anderson, 1986 ; Schoettler and Toth, 2014 ). Typical characteristics of HL (or sun) acclimated plants in comparison with LL (or shade) acclimated plants are:

• Increased thickness of leaves with more cell layers and larger cells (Björkman and Holmgren, 1963 ; Ludlow and Wilson, 1971 ; Wild and Wolf, 1980 ; Weston et al., 2000 ).
• Increased number of chloroplasts per cell (Anderson et al., 1973 ; Anderson, 1986 ) with reduced grana stacking (Anderson et al., 1973 ; Lichtenthaler et al., 1981 ).
• Higher Chl a/b ratio (Boardman, 1977 ; Wild, 1980 ; Lichtenthaler et al., 1981 ; Bailey et al., 2004 ) and increased β-carotene and xanthophyll cycle pigment levels (Anderson, 1986 ; Bailey et al., 2004 ).
• Higher photosystem II (PSII)/PSI ratio and smaller PSII antenna size (Schoettler and Toth, 2014 ; Albanese et al., 2016 ).
• Higher electron transport rates, higher CO 2 assimilation rates and higher light compensation points (Björkman and Holmgren, 1963 ; Ludlow and Wilson, 1971 ; Boardman, 1977 ; Wild, 1980 ).
• Higher energy dissipation capacity (Brugnoli et al., 1994 ; Demmig-Adams and Adams, 1996 ; Park et al., 1996 ; Ballottari et al., 2007 ; Mishra et al., 2012 ).

These characteristics apply to extreme sun and shade plants in the field, to sun, and shade leaves of the same individual plant in the field and to plants grown under different controlled light conditions in the lab.

In contrast to other environmental factors, the light intensity may vary in the short-term (seconds to minutes) by orders of magnitudes in an unpredictable manner such as on cloudy days. Particularly, plants at normally shady sites which are frequently exposed to HL, must properly adjust the photosynthetic capacity to overcome the challenges related to photo-oxidative damage under such fluctuating light conditions (Li et al., 2009 ). The fastest photoprotective response of plants and algae to rapidly increasing light intensities is the non-photochemical quenching (NPQ) of excess light energy in the antenna of photosystem II (PSII) (Müller et al., 2001 ; Jahns and Holzwarth, 2012 ; Ruban et al., 2012 ; Derks et al., 2015 ; Goss and Lepetit, 2015 ). Among the different components that contribute to the overall NPQ (Quick and Stitt, 1989 ; Walters and Horton, 1991 ; Nilkens et al., 2010 ), the pH-regulated qE component represents the main constituent of NPQ under most conditions and is the fastest (within minutes) inducible and relaxing component (Nilkens et al., 2010 ). In land plants, qE is strictly regulated by the thylakoid lumen pH (Krause et al., 1982 ) and requires the PsbS protein for rapid activation (Li et al., 2000 ). PsbS acts as a sensor of the lumen pH (Li et al., 2004 ) and is supposed to activate qE by conformational changes in PSII antenna proteins (Horton et al., 2005 ) through the interaction with LHCII complexes (Correa-Galvis et al., 2016 ; Sacharz et al., 2017 ).

Apart from this central function of PsbS, qE is also regulated by the xanthophyll zeaxanthin (Zx) (Demmig et al., 1987 ; Horton et al., 1996 , 2005 ; Nilkens et al., 2010 ), which is formed in high light in the de-epoxidation reactions of the xanthophyll cycle from violaxanthin (Vx) (Jahns et al., 2009 ). The function of Zx in NPQ, however, is not only limited to the pH-regulated qE mechanism, but Zx is also involved in more slowly relaxing NPQ states such as qZ (Dall'Osto et al., 2005 ; Nilkens et al., 2010 ) and qI (Adams et al., 2002 ; Demmig-Adams et al., 2006 ; Nilkens et al., 2010 ). In particular, the close kinetic correlation of Zx epoxidation and the recovery from photoinhibition (Jahns and Miehe, 1996 ; Verhoeven et al., 1996 ; Reinhold et al., 2008 ) supports a critical role of Zx in qI. This function is likely related to the sustained down-regulation of PSII, which has been observed along with the inactivation of Zx epoxidation in overwintering evergreen plants (Adams et al., 1995a , b ; Ebbert et al., 2005 ; Zarter et al., 2006b ).

Though activation and/or maintenance of different NPQ states are correlated with the presence of Zx, this does not allow any conclusions about a specific function of Zx in energy quenching (Jahns and Holzwarth, 2012 ). However, a direct function of Zx in qE in minor antenna complexes has been derived from transient absorption measurements performed with intact thylakoids (Holt et al., 2005 ) or isolated PSII antenna complexes (Ahn et al., 2008 ; Avenson et al., 2008 ). In contrast, an indirect function of Zx in trimeric light-harvesting complexes of PSII (LHCII) has been proposed on the basis of resonance Raman spectroscopy (Robert et al., 2004 ; Ruban et al., 2007 ). These contrasting observations imply that different quenching mechanisms and/or quenching sites with different roles of Zx contribute to NPQ. In fact, time-resolved Chl fluorescence measurements support the view that at least two different quenching sites/mechanisms are active in diatoms (Miloslavina et al., 2009 ), green algae (Amarnath et al., 2012 ) and vascular plants (Holzwarth et al., 2009 ). Measurements with intact leaves of Arabidopsis wild type and NPQ mutant plants identified two different quenching sites, termed Q1 and Q2, with different requirements for PsbS (involved in the activation of Q1) and Zx (required for activation of Q2; Holzwarth et al., 2009 ).

The increased NPQ capacity of high-light acclimated plants (Brugnoli et al., 1994 ; Demmig-Adams and Adams, 1996 ; Park et al., 1996 ; Ballottari et al., 2007 ; Mishra et al., 2012 ) is typically accompanied by the accumulation of higher levels of PsbS and Zx than under LL (Demmig-Adams et al., 2006 ; Zarter et al., 2006a ; Albanese et al., 2016 ). This underlines again the essential role of these two factors for NPQ. Recent work has shown that field-grown plants acclimated to natural HL conditions develop a higher NPQ capacity compared to plants grown under constant HL conditions in the lab (Mishra et al., 2012 ) and high NPQ capacities have been observed in evergreen plants acclimated to HL during winter (Demmig-Adams et al., 2006 ). Such high quenching capacities in evergreen plants have been correlated with a light-induced partial unstacking of the thylakoid membrane (Demmig-Adams et al., 2015 ). Interestingly, super-quenching states in the dinoflagellate Symbiodinium have recently been shown to be related to the activation of an energy spill-over mechanism of quenching (i.e., efficient energy transfer from PSII to PSI), which is also accompanied by structural rearrangement of the thylakoid membrane (Slavov et al., 2016 ).

In this work, we characterized the acclimation of Arabidopsis plants to different constant light intensities in comparison with plants grown under natural fluctuating light (NatL) conditions. We hypothesize that growing plants under fluctuating light might provide a better adaptation of the plants to high light stress. Analysis of the morphological, physiological, and biochemical characteristics indicated that NatL plants combine properties of LL and HL acclimated plants. NatL plants exhibited a high NPQ capacity among all plants grown at the different light regimes. Time-resolved Chl fluorescence analysis showed that this high NPQ capacity of NatL plants is based on an efficient qE quenching whose activation is accompanied by reversible changes in the thylakoid membrane stacking.

Materials and methods

Plant growth.

Arabidopsis thaliana (ecotype Col-0) plants were cultivated on soil (BP substrate, Klasmann-Deilmann GmbH, Geerste, Germany) under long day conditions (14 h light/10 h dark) at 20°C and three different light intensities: Low light (LL, 25 μmol photons m −2 s −1 ); normal light (NL, 100 μmol photons m −2 s −1 ) and high light (HL, 500 μmol photons m −2 s −1 ). LL and HL plants were transferred into the respective light regime after 2 weeks of growth under NL conditions. Plants grown under natural light (NatL) conditions were transferred to an east-facing balcony outside of the lab (Düsseldorf, Germany, 51°11′18.5″N 6°48′00.5″E). Plants were watered manually, because the site was sheltered from rain. Full sunlight exposure was only possible before noon due to shading of the plants by surrounding buildings. The daily photoperiod varied between 14 and 16 h. The median light intensity received by NatL plants was about 150 μmol photons m −2 s −1 , with a 95% quantile of 1230 μmol photons m −2 s −1 at its upper range (see Figure S1 ). For all experiments, about 5 weeks old plants were used for NL, HL, and NatL conditions, and about 6 weeks old plants for LL conditions.

Pigment analysis

Intact leaves or leaf discs were harvested and immediately shock frozen in liquid N 2 . After pestling, pigments were extracted with 1 ml of 100% acetone. After short centrifugation, samples were filtered through a 0.2 μm membrane filter (GE Healthcare, Buckinghamshire, UK) and stored at −20°C until analysis. Pigments were separated and quantified by HPLC analysis as described (Färber et al., 1997 ).

Isolation of chloroplasts and thylakoid membranes

Intact chloroplast were prepared according to Kley et al. ( 2010 ). In brief, 2–5 grams of dark-adapted leaves were kept for 2 h at 4°C and then homogenized in 25 ml of isolation medium (0.3 M sorbitol, 20 mM Hepes/KOH pH 7.6, 1 mM MgCl 2 , 1 mM MnCl 2 , 5 mM EDTA, 5 mM EGTA, 10 mM NaHCO 3 ) supplemented with 0.1% (w/v) BSA and 330 mg/l Na-ascorbate. The homogenate was gently filtered through one layer 50 μm Petex polyester mesh (Sefar, Thal, Switzerland) and then loaded on a Percoll cushion [50% (v/v) Percoll in isolation medium]. After centrifugation for 10 min at 4°C and 2000 × g, the resulting pellet, which contained intact chloroplasts, was gently resuspended in isolation buffer. The chloroplast suspension was centrifuged for 5 min at 4°C and 2,000 × g and finally resuspended in a small volume (100–250 μl) of isolation buffer. Thylakoid membranes were isolated from chloroplasts after osmotic shock with 5 mM MgCl 2 .

Determination of the Chl content of chloroplasts

Fifty microliters of four dilutions (1:10, 1:20, 1:50, and 1:100) of isolated intact chloroplasts were transferred to a Neubauer counting chamber and the number of chloroplasts was quantified via counting 4 out of 16 squares of the counting chamber. The Chl content per chloroplast was calculated on basis of the Chl concentration of each dilution.

SDS-PAGE and western blot analysis

SDS-PAGE was performed according to Laemmli ( 1970 ). 13.5% acrylamide gels were used and 8–20 μg total protein were loaded on the gel for each sample. Proteins were transferred to a PVDF membrane (BIORAD, Hercules, USA) using a discontinuous blotting system according to Kyhse-Andersen ( 1984 ). Coomassie and Ponceau S staining of gels and membranes, respectively, were used as loading and transfer controls. Anti-PsbS (1:8000, commissioned work by Pineda Antikörper Service, Berlin, Germany) was used as antibody. The second antibody (1:10000, anti-rabbit-IgG, Sigma-Aldrich) was detected by chemiluminescence (PicoLucent™, GBiosciences, St. Louis, USA). Chemiluminescence was detected using the LAS-4000 mini (Fujifilm, Tokyo, Japan). Band intensity was quantified using the freeware Image Studio Lite (LI-COR Biosciences, Lincoln, USA).

Spectroscopic determination of PSI, PSII, and Cyt b 6 f

For the determination of the PSI content, isolated thylakoids equivalent to 50 μmol Chl were suspended in 1.5 ml measuring medium [0.2% (w/v) n-dodecyl-β-D-maltoside, 30 mM KCl, 10 mM MgCl 2 , and 30 mM Hepes/KOH, pH 7.6]. After short centrifugation (45 s, 10,000 × g), 1.2 ml of the supernatant was transferred into a disposable polystyrene cuvette (Sarstedt, Nümbrecht, Germany). 10 mM Na ascorbate and 100 mM methyl viologen were added to the sample and mixed carefully before the measurement. PSI was quantified using the P700 emitter/detector unit of a DUAL-PAM 100 (Walz, Effeltrich, Germany). Only fully dark-adapted samples were measured. Precautions were made that no trembling of the cuvette or the cuvette holder disturbed the sensitive measurement. After calibrating the P700 signal, a 200 ms saturation pulse was applied to the sample and the maximum amplitude of the signal was quantified. The dark baseline resembles the PSI in a fully reduced state, whereas at the maximal amplitude, PSI is in a completely oxidized state. PSI content was calculated as follows: Δc = ΔI/I/(2.3 × ε × d), with ε = 2.53 cm 2 μmol −1 , specific for the Dual-PAM system used for the experiments.

The amounts of PSII and cytochrome (Cyt) b 6 f were calculated from differential spectra measured with a photometer in a range of 540–575 nm. In this approach, absorption changes of Cyt b 6 , Cyt f, Cyt 559 , and Cyt 550 were measured at different oxidation states (see below). The differential spectra were fitted against reference spectra and the amount of cytochrome b 6 f and PSII (Cyt 550 ) was calculated.

Isolated thylakoids equivalent to 50 μmol of Chl were incubated for 10 min in the measuring medium [0.02% (w/v) n-dodecyl-β-D-maltoside, 30 mM KCl, 0.1 mM EDTA, and 30 mM Hepes/KOH, pH 7.6] to ensure complete grana unstacking. After blanking, 1 mM potassium ferricyanide was added to fully oxidize the cytochromes. After 1 min of incubation the spectra were recorded (10 cycles). Subsequently, 10 mM Na ascorbate was added to partially reduce the cytochromes. Samples were incubated for 5 min and spectra were recorded again in the range of 540–575 nm (10 cycles). Finally, to fully reduce all cytochromes, a spatula tip of dithionite was added and the cuvette was sealed with paraffin oil (150 μl) to prevent reoxidation of the cytochromes by aerial oxygen. After 8 min of incubation on ice, the spectra were measured (10 cycles). Averages from all cycles of each treatment were used for calculating the amount of PSII (Cyt 550 ) and Cyt b 6 f.

NPQ measurements

Steady state Chl fluorescence was measured with the DUAL-PAM 100 (Walz, Effeltrich, Germany). Dark-adapted leaves were illuminated for 30 min at the respective actinic light intensity, followed by 30 min dark relaxation. Saturation pulses (200 ms, 4,000 μmol photons m −2 s −1 ) were applied to determine the NPQ as (Fm/Fm′ − 1) (Krause and Jahns, 2004 ). Electron transport rates were estimated according to Genty et al. ( 1989 ). The redox state of Q A was derived from the parameter qL = (Fm′− F)/(Fm′ − F 0 ′ ) × F 0 ′ /F according to Kramer et al. ( 2004 ). The transient NPQ was determined from fluorescence measurements during 10 min illumination at 53 μmol photons m −2 s −1 (for NL, HL, and NatL plants) or at 13 μmol photons m −2 s −1 (for LL plants).

P700 oxidation state

The redox state of P700 was determined with the DUAL-PAM-100 (Walz, Effeltrich, Germany) employing the saturation pulse method (Klughammer and Schreiber, 1994 ). In brief, leaves were illuminated at different light intensities in the range from 20 to 1,950 μmol photons m −2 s −1 and P700 absorbance changes were measured at 830 nm after 2 min of illumination at each light intensity. The P700 oxidation state was derived from the fraction of donor-side limited closed centers P700 + A, Y(ND).

OJIP transients

Chl fluorescence induction transients (Stirbet and Govindjee, 2011 ) were measured with a Handy PEA fluorometer (Hansatech Instruments, Norfolk, UK). Dark acclimated leaves were illuminated for 1 s with 3,500 μmol photons m −2 s −1 at a gain multiplication of 0.5. The nomenclature of this measurement O-J-I-P resembles the different fluorescence states, with O = origin, ground fluorescence (F 0 ); J, and I = intermediate states based on the reduction of Q A (O-J phase) and the electron transfer to the PQ pool (J-I phase); P = peak, maximum fluorescence (Fm).

Ultrafast fluorescence kinetics

Ultrafast lifetime measurements were carried out as described (Holzwarth et al., 2009 ) with detached leaves held in a rotating cuvette, front-face excitation of the upper side of the leaf, using laser pulses of 663 nm and a repetition rate of 4 MHz. F max measurements were performed with dark-acclimated leaves infiltrated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea. F NPQ measurements were started after 30 min pre-illumination at 600 μmol photons m −2 s −1 using a mixture of red and amber light-emitting diodes. Kinetic data analysis and kinetic compartment modeling were performed as described (Holzwarth et al., 2009 ; Slavov et al., 2016 ).

Light microscopy

Leaf material was fixed and prepared as specified in Table ​ Table1. 1 . Semi thin (2 μm) leaf cross sections were cut with a microtome (Leica Ultracut, Leica Microsystems, Bensheim, Germany) and leaf cross sections were stained for 2 min at 60°C with 1% (v/v) methylene blue, 1% (v/v) azur II in a 1% (v/v) aqueous borax solution. After washing and drying, cross sections were examined using a Zeiss Axiocam camera in in a Zeiss Axiovert 135 microscope (Zeiss, Oberkochen, Germany).

Sample preparation for transmission electron microscopy .

Protocol for combined conventional and microwave-proceeded fixation, dehydration and resin embedding of Arabidopsis rosette leaf tissue for histological and ultrastructural analysis .

Transmission electron microscopy

Transmission electron microscopy images were obtained with a FEI Tecnai Sphera G2 (FEI, Hillsboro, Oregon, USA) microscope. For comparative histological and ultrastructural analysis, microwave proceeded fixation, substitution and resin embedding of rosette leaves was performed as specified in Table ​ Table1. 1 . Sectioning and microscopy analysis was carried out as described previously (Daghma et al., 2011 ).

Lipid analysis

Total lipids were extracted from 200 mg of leaves with chloroform/methanol. Harvested leaf material was immediately transferred into glass vials containing boiling water and boiled for 20 min to inhibit all lipase activity. After transferring the leaves into a fresh glass vial, 1 volume of chloroform:methanol (2:1) was added and samples were gently mixed. The green supernatant was transferred into a fresh glass vial and the leaf material was washed in a second step with 1 volume chloroform:methanol (1:2). The green supernatants were pooled and stored in a glass vial with Teflon® cap at −20°C. The leaf material was dried overnight in a drying chamber at 70°C and the dry weight was determined. Membrane phospholipids and glycolipids were quantified by direct infusion nanospray mass spectrometry on an Agilent 6530 quadrupole time-of-flight instrument (Gasulla et al., 2013 ).

Gas exchange measurements

CO 2 assimilation rates and light compensation points were derived from light response curves determined by gas exchange measurements [LI-COR-6400XT (LI-COR, Nebraska, USA)] under controlled CO 2 conditions (400 ppm CO 2 , flow rate 300 μmol s −1 , 102.4 kPa) at 20°C. Before each measurement, plants were light-acclimated for 15 min at 500 μmol photons m −2 s −1 . Light response curves were measured from the lowest (25 μmol photons m −2 s −1 ) to the highest (2,000 μmol photons m −2 s −1 ) light intensity. Leaves were acclimated to the respective light intensity for 3 min. For determination of the maximum assimilation rate (P max ) and the light compensation point (LCP), curves were fitted with Prism® applying a single exponential function.

Statistical analysis

Differences among the analyzed variables under the different growth light regimes were evaluated statistically using Sigma Plot 12.5. For each variable, significant differences among growth light conditions were determined by ANOVA or—when neither the error normality nor the variance homogeneity criteria were fulfilled—by the Kruskall Wallis test. Subsequently, specific differences between light growth regimes were evaluated by the Holm-Sidak test (in the case of ANOVA) or by the Dunn's test (in case of the Kruskall Wallis test). Significant differences ( p < 0.05) are indicated.

NatL plants exhibit higher light use efficiency than plants grown under continuous light

Plants grown under constant high light conditions showed increased growth compared to those grown under constant low light as judged from the phenotype of 6 week-old plants (Figure ​ (Figure1A). 1A ). The size of NatL plants was similar to that of HL plants. However, in contrast to all other plants, NatL plants already developed flowers after 6 weeks (Figure ​ (Figure1A), 1A ), indicating that NatL conditions triggered a faster plant development. This was supported by analysis of the fresh weight (FW) per cm 2 leaf area, which increased from about 10 mg in LL plants to 25 mg in HL plants, whereas NatL plants showed highest values of about 30 mg (Figure ​ (Figure1B). 1B ). The dry weight (DW)/FW ratio showed no pronounced differences among the different plants (Figure ​ (Figure1B), 1B ), reflecting that the DW showed similar relative differences among the different plants as observed for the FW. Moreover, NatL plants displayed high rates of net photosynthesis similar to HL plants (Figure ​ (Figure1C). 1C ). The median light intensity under NatL conditions (about 150 μmol photons m −2 s −1 ) was about 30% of that under HL conditions (500 μmol photons m −2 s −1 ), but the corresponding difference in biomass was clearly much lower. We therefore conclude that plants grown under NatL have higher light use efficiency than HL grown plants.

Plant growth and CO 2 assimilation rates. (A) Typical phenotype of 6 weeks-old plants. Please note that 6 weeks-old plants are shown here to illustrate the differences in development, only. All analyses have been performed with about 5 weeks-old plants, and thus before onset of flowering. (B) Fresh weight (FW) of leaves in mg cm −2 and dry weight (DW) per FW in% (100 × DW/FW). Mean ± SE of six independent samples are shown. Significant differences (Holm-Sidak test, p = 0.05) are indicated. (C) Light response curves of NL, HL, and NatL grown plants. Insert, light compensation point derived from exponential fits of the assimilation curves. Mean values ± SE of 4–6 independent measurements are shown. Significant differences (Holm-Sidak test, p < 0.05) are indicated. Due to their small size, LL plants could not be measured.

Leaf morphology of NatL plants is similar to that of HL plants

Microscopic analysis of leaf cross sections (Figures 2A–D ) revealed a similar leaf thickness of about 115–130 μm in LL and NL plants, while growth under HL and NatL resulted in about 2-fold thicker leaves of about 270–280 μm (Figure ​ (Figure2E). 2E ). The increased leaf thickness of HL and NatL plants was mainly due to elongated parenchyma cells (Figure ​ (Figure2F) 2F ) and only partly related to an increased number of cell layers, which varied between 6 layers in LL plants, 7 layers in NL, and NatL plants, and 8 layers in HL plants. The number of chloroplasts per mesophyll cell increased from about 4 in LL plants to 6 in NL plants and 8 in HL and NatL plants (Figure ​ (Figure2G). 2G ). An only slight difference was determined for the Chl content of chloroplasts (Figure ​ (Figure2H), 2H ), which tended to decrease with increased growth light intensities, and was lowest in NatL grown plants.

Light microscopic analysis of leaf cross-sections . Upper panel: Light microscopic images of leaf cross-sections from (A) LL plants, (B) NL plants, (C) HL plants, and (D) NatL plants. Lower panel: Quantitative analysis of (E) leaf thickness, (F) the number of cells per cm 2 leaf area, (G) the number of chloroplasts per cell and (H) the number of Chl per chloroplast. Significant differences (Dunn's test, p < 0.05) are indicated. Data represent mean values ± SE of at least 116 leaf cross-sections in (E) , of at least 32 leaf cross-section in (F) , of cells from at least 6 images in (G) , and of at least 3 independent chloroplast preparations in (H) .

Thylakoid membranes of NatL plants share structural properties of LL and HL plants

The thylakoid membrane organization was investigated by transmission electron microscopy (Figures 3A–D ). Chloroplasts from LL plants showed the highest density of thylakoid membranes in comparison to those from other growth conditions. In general, more and thicker grana stacks were detectable, which were connected by a large number of stroma lamellae (Figure ​ (Figure3A). 3A ). On average, 6 membranes per grana stack and a grana width of about 570 nm were found for LL plants (Figures 3E,F ). The overall thylakoid structure of NL plants (Figure ​ (Figure3B) 3B ) was similar to that of LL plants, but the number of membranes per grana stack was reduced to about 5 and the grana width to about 470 nm (Figures 3E,F ).

Transmission electron microscopy analysis of chloroplasts . Upper panel: Electron microscopic images of the thylakoid membrane structure of (A) LL plants, (B) NL plants, (C) , HL plants, and (D) NatL plants. Round dark structures (arrow heads) represent plastoglobules. Lower panel: Quantification of (E) the width of grana stacks, (F) the number of membranes per grana stack and (G) the number of plastoglobules. Mean values ± SE of at least six images are shown. Significant differences (Dunn's test, p < 0.05) are indicated.

In contrast to LL and NL plants, the overall amount of thylakoid membranes and the overall degree of grana stacking was strongly reduced in HL plants, so that the relative fraction of stroma exposed membranes increased (Figure ​ (Figure3C). 3C ). Grana stacks in HL plants typically consisted of only 3 membranes and the grana width was reduced to about 390 nm (Figures 3E,F ). In NatL plants (Figure ​ (Figure3D), 3D ), the thylakoid membrane system was similar to that in HL plants, but the number of membranes per grana stacks was significantly higher (4 membranes per granum, Figure ​ Figure3F). 3F ). However, in contrast to all other plants, NatL grown plants showed both, thin grana of 2 or 3 membranes as in HL plants but also some thicker grana with more than 6 membranes within the same chloroplast. This indicates that the thylakoid membrane organization in NatL plants shares properties of LL and HL acclimated chloroplast.

Strikingly, also the number of plastoglobules per chloroplast varied among the plants from different growth conditions (Figure ​ (Figure3G). 3G ). While about 8 plastoglobules per chloroplast cross-section were found in LL and NL plants, the number increased to 10 in HL plants and was highest in NatL plants, with 12 plastoglobules per chloroplast cross-section.

Chloroplast lipid composition is similar in plants from all growth light conditions

Total leaf lipid extracts were further analyzed with respect to lipid classes and fatty acid composition. The relative contribution of glycolipids and phospholipids to the total amount of lipids was similar among all growth conditions (Figure ​ (Figure4). 4 ). About 75% of the lipids in leaves were glycolipids (Figure ​ (Figure4A), 4A ), with monogalactosyldiacylglycerol (MGDG, 50%) being the major constituent, followed by digalactosyldiacylglycerol (DGDG, 20%) and sulfoquinovosyldiacylglycerol (SQDG, 5%), in agreement with previous findings (Benson et al., 1959 ; Welti et al., 2002 ). The remaining 25% of membrane glycerolipids in leaves were phospholipids (Figure ​ (Figure4B), 4B ), with phosphatidylcholine (PC) being the main constituent (12–16%). The amount of PC increased with increasing growth light intensity in LL, NL, and HL plants, and the PC content of NatL plants was similar to that of NL plants. In contrast, the amount of phosphatidic acid (PA) was highest in LL and NatL grown plants, while the amount of PS was significantly lower only in NL grown plants in comparison with LL and HL grown plants (Figure ​ (Figure4B). 4B ). Also the saturation level of the fatty acids was very similar in the plants grown at different light regimes (Table S1 ). In conclusion, different growth light conditions do not have a pronounced impact on the lipid composition of the thylakoid membrane. Therefore, it is unlikely that the lipid composition is the key determinant for the observed differences in thylakoid membrane organization.

Lipid composition of leaves. (A) Relative amount of glycolipids. (B) Relative amount of phospholipids. MGDG, Monogalactosyldiacylglycerol; DGDG, Digalactosyldiacylglycerol; SQDG, Sulfoquinovosyldiacylglycerol; PA, Phosphatidic acid; PS, Phosphatidylserine; PI, Phosphatidylinositol; PG, phosphatidylglycerol; PE, and phosphatidylethanolamine; PC, Phosphatidylcholine. Mean values ± SD of five independent samples are shown. Significant differences [Holm-Sidak test, p < 0.05, for (A) ; Dunn's test, p < 0.05, for (B) ] are indicated.

The protein and pigment composition of thylakoid membranes from NatL plants share characteristics of LL and HL plants

To assess differences in the composition of the photosynthetic electron transport chain, the protein and pigment content of the thylakoid membrane was analyzed. No pronounced differences in the PSI and PSII content on Chl basis were determined among plants from different growth conditions (Table ​ (Table2). 2 ). In general, the amount of PSI (1.7–2 mmol per mol Chl) was slightly lower compared to that of PSII (2.0–2.5 mmol per mol Chl), resulting in PSII/PSI ratios of about 1–1.3. In NL plants, significantly more PSI was found in comparison to other growth light conditions, whereas PSII was most abundant in HL plants. NatL plants showed similar PSI amounts as LL and HL plants, but lower amounts of PSII than HL plants. In contrast, the amount of Cyt b 6 f varied strongly (in the range from 0.3 to 0.8 mmol Cyt b 6 f per mol Chl) and showed a positive correlation with increasing constant growth light intensity (HL>NL>LL). In HL plants, about 2–3 fold higher levels of Cyt b 6 f were determined compared to plants from other growth conditions (Table ​ (Table2). 2 ). This particular response of the Cyt b 6 f content to different growth light intensities has been reported before (Leong and Anderson, 1984 ), so that the low Cyt b 6 f content of NatL plants suggests a LL acclimated electron transport chain on basis of the abundance of protein complexes. In contrast, typical HL acclimation characteristics were determined for NatL plants with respect to the PsbS level and the xanthophyll cycle pigment pool (VAZ pool) size. Both the PsbS content and the VAZ pool size increased with increasing growth light intensities and highest levels were found in NatL plants (Table ​ (Table2, 2 , Figure S2 ), in agreement with the literature (Mishra et al., 2012 ). Hence, NatL plants share properties of both LL and HL acclimated plants at the level of the protein and pigment composition of the thylakoid membrane.

Pigment and protein composition .

The pigment composition of thylakoid membranes was derived from HPLC analyses. Carotenoid levels are given in mmol (mol Chl) −1 . Mean values ± SD of at least 10 samples are shown. The amount of PSII, PSI, and Cytb 6 /f (expressed in mmol (mol Chl) −1 ) was determined from spectroscopic measurements of the respective activities. Mean values ± SD of 5 independent experiments are shown. PsbS levels were derived from Western blot analyses. The values represent relative amounts of PsbS normalized to the amount of NL plants. Mean values ± SD of five independent experiments are shown. For all parameters, significant differences (Holm-Sidak or Dunn's test, p < 0.05) are indicated by superscripted letters. The ratios of protein complexes were calculated from the respective mean values .

NatL plants combine light utilization characteristics of LL and HL plants

The time course of the fluorescence increase from Fo to Fm (OJIP transient) provides information about electron transfer between PSII and PSI (Stirbet and Govindjee, 2011 ). The O-J transient reflects the reduction of Q A in PSII, the J-I phase the reduction of the plastoquinone (PQ) pool, and the I-P phase indicates the reduction of the acceptor side in PSI. As shown in Figure ​ Figure5A, 5A , the overall fluorescence increase was fastest in LL plants. This was apparent for both, the intra-PSII electron transfer to Q A (O-J phase) and the electron transfer to the PQ pool (J-I phase). Intermediate kinetics were found for NL plants, while HL and NatL plants showed slowest reduction of both Q A (O-J) and PQ (J-I), although a distinct plateau of the I-phase was not clearly distinguishable from the J-P transient (Figure ​ (Figure5A 5A ).

Electron transfer from PSII to PSI. (A) Chl fluorescence induction transients normalized to the total amplitude from the O to the P state (upper panel). The lower panel depicts the O to J phase (left) and the J to P phase (right), again normalized to the respective total amplitude. The normalization allows for direct comparison of the fluorescence induction kinetics. O, original fluorescence, corresponding to Fo; J and I, intermediate states; P, fluorescence peak, corresponding to Fm. Mean values of 10 measurements are shown, SD was <0.04. (B) P700 oxidation state at five different illumination intensities. Mean values ± SE of at least five independent samples are shown. Significant differences (Holm-Sidak or Dunn's test, p < 0.05) are indicated.

The kinetics of Q A reduction are known to reflect the functional antenna size of PSII (Malkin et al., 1981 ) with a larger antenna leading to a faster Q A reduction. This suggests that LL plants possess the largest functional antenna, followed by NL plants and finally HL and NatL plants. This interpretation is in agreement with the determined Chl a/b ratios, which increased with increasing light intensities during growth at continuous light (Table ​ (Table2). 2 ). However, NatL showed a slow O-J increase (like HL plants) although the Chl a/b ratio was similar to NL plants, indicating that the antenna composition is not the only determinant for efficient Q A reduction in PSII. Electron transfer was further monitored through measurements of the P700 oxidation state at different actinic light intensities (Figure ​ (Figure5B). 5B ). The data determined for LL, NL, and HL plants revealed the expected differences of the P700 oxidation state. LL plants showed a high oxidation of P700 (of about 80%) at rather low light intensities of 166 μmol photons m −2 s −1 , while similar oxidations states of P700 were reached only at higher light intensities in NL plants (at 340 μmol photons m −2 s −1 ) and HL plants (at 825 μmol photons m −2 s −1 ). Strikingly, NatL plants showed similar PSI oxidation states as LL plants at low actinic light intensities, but similar PSI oxidation states as HL plants at the two highest analyzed light intensities (Figure ​ (Figure5B). 5B ). This suggests that NatL plants share properties of both LL and HL plants, and reflects the ability of NatL plants to cope efficiently with both low and high light intensities. It has been shown earlier, that the oxidation state of P700 is crucial for the photoprotection of PSI under high light (Tikkanen et al., 2014 ). To keep P700 in a partially oxidized state a low light might thus represent an advantage under rapidly fluctuating light conditions.

The light utilization capacity of the plants was further studied by Chl fluorescence and absorption spectroscopy under steady state conditions at the end of 30 min illumination at three different actinic light intensities (Table ​ (Table3). 3 ). At the level of electron transport and the fraction of oxidized Q A (as reflected by the parameter qL), NatL plants showed properties of HL plants. The same held true for the NPQ capacity. However, NatL plants showed even a slightly higher capacity of pH-regulated qE quenching than HL plants, not only at the level of the maximum qE under light-saturated steady state conditions, but also for the transient qE under light-limiting conditions (Table ​ (Table3). 3 ). Differences in the maximum qE capacity maybe related to differences in the lumen pH, and/or the amount of PsbS or Zx. In fact, NatL plants showed slightly higher PsbS levels than HL plants (Table ​ (Table2, 2 , Figure S2 ), but significantly lower Zx levels (Table ​ (Table3). 3 ). We assessed the lumen acidification by DIRK (dark interval relaxation kinetics) analysis of electrochromic absorption changes at 515 nm (Takizawa et al., 2007 ). The total proton motive force ( pmf ) (= ECS total ) was found to be statistically not significantly different among all types of plants, but the fraction of the pmf stored as ΔpH (ECS inv ) was highest in NatL plants and LL plants (Table ​ (Table3). 3 ). This indicates that the lumen pH is significantly lower in NatL and LL plants compared to NL and HL plants. The proton conductivity of the ATP synthase (gH + ), however, was lower in LL plants (about 14–17 s −1 ) than in all other plants (about 23–34 s −1 ). Hence, also at the level of pmf partitioning and proton consumption by the ATP synthase, NatL plants combine properties of LL plants ( pmf partitioning) and HL plants (proton consumption). The high qE capacity of Natl plants is therefore likely determined by combination of increased PsbS levels (as in HL plants) and a low lumen pH (as in LL plants).

Light utilization parameters at the end of 30 min illumination at three actinic light (AL) intensities: 340, 825, and 1950 μmol photons m −2 s −1 (μE) .

The electron transport rate (ETR), the fraction of oxidized Q A (qL), and the NPQ parameters qE and qI were derived from Chl fluorescence analysis. The relative Zx content (in % of the total VAZ pool) was determined by HPLC analyses. The total pmf (ECS total ), the fraction of the pmf stored as ΔpH (ECS inv ) and the proton conductivity of the ATP synthase (gH + ) was derived from DIRK (dark interval relaxation kinetics) analysis of electrochromic absorption changes. The maximum value of the transient NPQ was determined from Chl fluorescence quenching analyses at non-saturating actinic light intensities (10 μE for LL plants and 50 μE for NL, HL, and NatL plants). Mean values ± SD of 3–6 independent experiments are shown. For all parameters, significant differences (Holm-Sidak or Dunn's test, p < 0.05) are indicated by superscripted letters .

The high qE capacity of HL plants, but not of NatL plants, is based on energy transfer to PSI

We further investigated the underlying quenching mechanisms by ultrafast fluorescence measurements. It was not possible to perform these measurements with LL plants due to the small leaf size of these plants. Analysis of the fluorescence decay kinetics measured at 686 nm (Figure ​ (Figure6) 6 ) revealed similar average lifetimes (τ av ) of about 1.3 ns in the dark-adapted F max state of NL, HL, and NatL plants (Table ​ (Table4). 4 ). The accelerated decay in the light-adapted state (F NPQ ) reflects the NPQ induction of NPQ in all cases. In comparison with NL plants (τ av = 380 ps), a slightly faster decay was found for HL plants (τ av = 320 ps) and a much faster decay for NatL plants (τ av = 130 ps), reflecting the most efficient quenching in NatL plants. These lifetimes corresponded to NPQ values of 2.6 (NL plants), 3.1 (HL plants), and 8.5 (NatL plants). For NL and HL plants, the NPQ values were somewhat higher but still similar to those derived from steady state fluorescence measurements (Table ​ (Table3), 3 ), while the NPQ value was much higher for NatL plants. This discrepancy is related to the fact that steady state NPQ values are determined from fluorescence emitted at wavelength >720 nm, while the NPQ values obtained from time-resolved measurements were derived from the fluorescence at 686 nm. Obviously, the NPQ at this PSII specific wavelength is much higher in the red region as compared to the far-red region.

Normalized fluorescence decays in Arabidopsis leaves . Fluorescence decay was measured in either unquenched dark-acclimated state (Fmax) or in the quenched light-acclimated state (F NPQ ). The excitation wavelength was 663 nm and the emissions measured at 683 nm. The faster decay in the F NPQ state indicates the activation of fluorescence quenching. Note that plants grown under NatL conditions exhibited the strongest quenching.

Average lifetimes and rate constants of F max and F NPQ components in NL, HL and NatL grown A. thaliana plants .

Upper part: Average lifetimes τ av [ps] of the fluorescence decay measurements at 686 nm under F max and F NPQ conditions shown in Figure S3 and the corresponding NPQ values. Middle part: Rate constants k D [ns −1 ] for PSII antenna deactivation of unconnected (PSII) and connected (PSII-C) PSII reaction centers under F max and F NPQ conditions. Lower part: Lifetime τ [ps] of the detached PSII antenna and the relative decrease of the PSII antenna cross-section (in% of the total PSII antenna). Errors in the values were in the range of ± 5–10% .

Decay-associated spectra (DAS), which carry both, spectral and kinetic information, were derived from global and target analysis (van Stokkum et al., 2004 ; Holzwarth et al., 2009 ; Slavov et al., 2016 ; Figure S3 ). In Arabidopsis leaves, such analyses result in identification of 4 components related to PSI (lifetimes ranging from 4 to 100 ps) and at least 3 components related to PSII (lifetimes ranging from 35 ps to 2 ns; Holzwarth et al., 2009 ; Miloslavina et al., 2011 ). Analysis of the PSII related spectra allowed for determination of the rate constant k D , which represents the non-photochemical deactivation rate in the PSII-attached antenna and is thus a direct measure of NPQ (Table ​ (Table4). 4 ). NL plants showed an increase of k D,PSII from 0.3 ns −1 in the dark-adapted state (k D,max,PSII ) to 1.8 ns −1 in the light-adapted (k D,NPQ,PSII ) state, in accordance with former studies (Holzwarth et al., 2009 ; Miloslavina et al., 2011 ). Moreover, also the light-induced detachment of a fraction of LHCII (k D,LHCII , Table ​ Table4), 4 ), which gives rise to the PsbS-dependent activation of the quenching site Q1 (Holzwarth et al., 2009 ; Miloslavina et al., 2011 ), was detectable. Compared to that, NatL plants showed the same general features, but both k D,LHCII and k D,NPQ, PSII were higher than in NL plants, reflecting an increased quenching involving the PsbS-dependent Q1 site and the Zx-dependent Q2 site, respectively.

In contrast to NL and NatL plants, it was not possible to fit the data obtained with HL plants with the classical kinetic schemes for separated PSII and PSI centers (Holzwarth et al., 2009 ). Instead it was required to assume a heterogeneous PSII pool, with a fraction of PSII being connected to PSI (PSII-C) to obtain satisfying fits of the data, as has been described recently for HL acclimated microalgae (Slavov et al., 2016 ). This type of quenching is based on an energy transfer to PSI and requires a reorganization of the thylakoid membrane structure, by allowing direct contact between PSII and PSI, which is usually prevented by the heterogeneous distribution of PSII (in grana stacks) and PSI (in stroma lamellae). In addition to this quenching mechanism, also the PsbS-dependent Q1 site becomes activated by high light in HL plants (Table ​ (Table4, 4 , Figure S3 ). However, the corresponding rate constant k D,LHCII was lower than in NL and NatL plants, indicating a less efficient quenching in Q1 in HL plants.

In conclusion, the analyses of ultrafast fluorescence kinetics underline that the high NPQ capacities of HL and NatL plants are based on different mechanisms. In HL plants, energy transfer to PSI is the major NPQ mechanism, whereas more efficient quenching related to the Q1 and Q2 site is responsible for the high NPQ in NatL plants.

Activation of qE in NatL plants involves rapidly reversible thylakoid membrane reorganization

To assess a possible rearrangement of the thylakoid membrane structure upon short-term acclimation to high light, electron microscopic images of chloroplasts from dark acclimated leaves were compared with those from light-acclimated leaves (30 min at 1,500 μmol photons m −2 s −1 ) and subsequently re-darkened (10 min) leaves (Figure ​ (Figure7). 7 ). For LL plants (Figures 7A–C ) and NL plants (Figures 7D–F ), no significant changes in the membrane structure were detectable upon transition from the dark-acclimated to the light-acclimated state (Figures 7M,N ). In contrast, HL plants (Figures 7G–I ) exhibited significant unstacking of grana after 30 min of illumination, but the unstacking was not reversible within 10 min of re-darkening (Figure ​ (Figure7M). 7M ). NatL plants (Figures 7J–L ), however, showed both light-induced grana unstacking and restacking after 10 min of re-darkening (Figure ​ (Figure7M). 7M ). The light-induced increase of the grana height was more pronounced in NatL than in HL plants and only NatL plants showed a significant broadening of the grana stacks by about 35% parallel to unstacking (Figure ​ (Figure7N). 7N ). This broadening was fully reversible during 10 min of re-darkening while the changes in grana height were only partially reversible (Figures 7M,N ), suggesting that tight packing of grana stacks as in LL and NL plants may prevent light-induced grana unstacking. Structural rearrangement of the membrane in response to high light might thus require a reduced degree of grana stacking in the dark-acclimated state, as observed in HL and NatL grown plants. However, more pronounced unstacking was observed in NatL plants, even though the grana stacks found in NatL plants were thicker compared to those in HL plants. Thus, growth under NatL conditions provides increased flexibility of thylakoid membranes.

Structural dynamics of thylakoid membrane stacking . Upper panel: Transmission electron microscopic images of thylakoid membranes of LL (A–C) , NL (D–F) , HL (G–I) , and NatL (J–L) plants in the dark- and light acclimated state, and after 10 min of re- darkening. Lower panel: Quantitative analysis of (M) grana height and (N) grana width. 16–20 images were analyzed for each condition. The light-adapted state was induced by 30 min illumination with white light at an intensity of 1000 μmol photons m −2 s −1 . Significant differences (Holm-Sidak test, p < 0.05) as compared to the respective dark-acclimated state are indicated.

Limitations of the comparison of indoor and outdoor grown plants

The comparability of characteristics of field-grown plants with those grown under controlled lab conditions is limited by the unknown impact of other environmental factors than light. To minimize such uncertainties, NatL plants were grown in the same soil and pots as all other plants, and all plants were watered manually to accomplish similar soil humidity. Furthermore, all plants were grown under long-day conditions (14 h light under constant light conditions and between 14 and 16 h light under NatL condition) to minimize the possible impact of differences in the photoperiod. Moreover, NatL plants were grown in periods when the outside temperature was between 15 and 25°C, which was in the range of the temperature in the lab (20°C). Since the saturation level of fatty acids, which represents a reliable indicator of long-term temperature acclimation (Falcone et al., 2004 ) was similar in all plants (Table S1 ), it can be assumed that indoor and outdoor grown plants did not differ in the general long-term acclimation to temperature.

However, daily changes in the ambient temperature have direct effects on enzyme activities and diffusion dependent processes, which may have impact on the overall metabolism, from nutrient uptake to single biochemical reactions. Importantly, temperature fluctuations will further alter the vapor pressure deficit (VPD) at a given relative air humidity. Recent work has shown, that changes in the VPD related to a temperature change of about 10°C alter both the size and aperture of stomata, and thus have a pronounced impact on water use efficiency (Arve et al., 2017 ). However, experiments with rice plants revealed, that the impact of fluctuating temperature, CO 2 and humidity has less impact on NPQ and ETR than fluctuating light (Yamori, 2016 ). Hence, fluctuating temperature, CO 2 and humidity predominantly affect water use efficiency and carbon fixation in the Calvin Benson Bassham cycle rather than direct regulation of NPQ and chloroplast structure. In addition to the photoperiod, temperature is a key determinant of the flowering time (Song, 2016 ) and thus of the development of plants. In indoor grown Arabidopsis plants, increase of the temperature generally triggers earlier flowering (Blázquez et al., 2003 ). However, fluctuating temperature conditions as experienced by field-grown plants strongly reduces the control of flowering time by temperature, leaving the photoperiod as the major determinant of FT under field conditions (Song, 2016 ). We therefore assume that fluctuations in temperature, VPD, air humidity, and CO 2 concentrations may mainly influence water use efficiency, biomass accumulation and development of NatL plants, but not the light utilization characteristics at the level of the electron transport chain. Moreover, the parameters studied here are known to be markedly influenced in response to changes of only the growth light intensity. Therefore, it is reasonable to assume that the different growth conditions used in this work provide a reliable basis for studying specific differences in acclimation to different growth light regimes.

Upper and lower limits of growth light intensities determine the characteristics of NatL plants

Plants grown under constant LL and HL intensities showed the well-known differences in leaf morphology and photosynthetic capacities (for details and references see Introduction). This was apparent from leaf thickness and CO 2 assimilation (Figure ​ (Figure1), 1 ), and the morphological and functional characteristics of chloroplasts and thylakoid membranes (Figures ​ (Figures2 2 – 5 ). NatL plants received median light intensities similar to that of NL plants, but achieved combined LL and HL properties as obvious from the characteristics of the composition and function of the electron transport chain. We therefore conclude that the upper and lower limits of growth light intensities (Figure S1 ) rather than the mean light intensity determine the light acclimation characteristics of plants.

Unique thylakoid membrane composition provides flexible light utilization in NatL plants

The acclimation of plants to fluctuating light intensities in the field requires a flexible adjustment of the photosynthetic capacity to cope with rapid changes of non-saturating and saturating light intensities. Our analyses show that NatL plants acquired properties of both HL plants (e.g., leaf morphology, CO 2 assimilation, and electron transport rates) and LL plants (e.g., Chl a/b ratio, lumen acidification), but further developed unique features (e.g., thylakoid membrane organization and dynamics). Hence, NatL combine different characteristics to ensure highly flexible light utilization in response to fluctuating light intensities.

At the level of photosynthetic electron transport, the amount of the Cyt b 6 /f complex is supposed to be the major site of photosynthetic flux control, because plastoquinol oxidation is the rate-limiting step of electron transport (Schoettler and Toth, 2014 ). The low abundance of Cyt b 6 /f in NatL plants (Table ​ (Table2) 2 ) represents a typical characteristic of LL plants, in line with the high fraction of oxidized P700 at low actinic light intensities in both LL and NatL plants (Figure ​ (Figure5B). 5B ). Furthermore, the ratios of PSII/Cyt b 6 f and PSI/Cyt b 6 f determined for NatL, also resembled the ratios of LL plants and were much higher than that of HL plants (Table ​ (Table2). 2 ). However, at high actinic light intensities, the P700 oxidation state (Figure ​ (Figure5B), 5B ), the redox state of Q A (parameter qL, Table ​ Table3) 3 ) and the dynamics of the reduction of the electron transport chain (OJIP transients, Figure ​ Figure5A) 5A ) of NatL plants were similar to that of HL plants. Obviously, a low Cyt b 6 /f content is not necessarily the key determinant for the redox state of the photosynthetic electron transport chain and of the electron transport characteristics.

Alternatively, differences in the membrane fluidity or the protein/lipid ratio may account for the observed electron transport characteristics of NatL plants. The lipid composition is known to have strong impact on membrane fluidity (Los and Murata, 2004 ; Mullineaux and Kirchhoff, 2009 ), which in turn might affect electron transport characteristics (Berry and Bjorkman, 1980 ; Los et al., 2013 ). However, the relative amounts of glycolipids and phospholipids, as well as the saturation level of fatty acids did not reveal significant differences among the plants from different growth conditions (Figure ​ (Figure4, 4 , Table S1 ). The protein density and the supramolecular organization of photosystems are known to influence the mobility of small molecules and large protein supercomplexes (Kirchhoff, 2014 ). Indeed, the amount of lipids per photosystem was strongly reduced in chloroplasts from NatL and HL plants as compared to LL and NL plants (Table ​ (Table5). 5 ). It can thus be speculated that the higher protein density in NatL and HL plants is responsible for more efficient electron transport at high light intensities.

Amount of Chl, lipids and protein complexes per chloroplast .

The values for the amount of Chl (a+b) ± SD were taken from Figure ​ Figure2H. 2H . Superscripted letters indicate significant differences (Holm-Sidak or Dunn's test, p < 0.05). All other values were calculated from the respective mean values determined in relation to Chl .

Light-regulated thylakoid membrane dynamics provide a high NPQ capacity of NatL plants

At the morphological level, NatL exhibited specific characteristics with respect to the thylakoid membrane structure (Figure ​ (Figure3) 3 ) and its light-dependent dynamics in the short-term (Figure ​ (Figure7). 7 ). The thylakoid membrane structure of NatL plants was similar to that of HL plants, but more heterogeneous with respect to the number of membranes per granum (Figure ​ (Figure3). 3 ). Moreover, chloroplasts from NatL plants contained the highest number of plastoglobules (Figure ​ (Figure3). 3 ). Plastoglobules are lipid bodies in chloroplasts (Lichtenthaler, 1968 ), which are in physical contact with the thylakoid membrane in stroma exposed regions and supposed to function in lipid storage and biosynthesis (Austin et al., 2006 ). The number and size of plastoglobules varies not only during plant development and plastid differentiation, but also under oxidative stress conditions (Rottet et al., 2015 ). Hence, the observed differences in the plastoglobule content likely represent different levels of acclimation to photo-oxidative stress.

Another specific feature of NatL plants was the rapidly light-inducible (with 30 min) and dark-reversible (within 10 min) switch in the grana structure (Figure ​ (Figure7). 7 ). The light-induced increase of the grana width was only detectable in NatL plants and occurred in parallel to the activation of NPQ. Similar changes have been described recently for sunlight grown Monstera plants (Demmig-Adams et al., 2015 ), which are also characterized by a high NPQ capacity. A high light-regulated flexibility of the thylakoid membrane might thus represent a key factor for the high NPQ of NatL grown plants. These structural changes might be promoted by high levels of PsbS and VAZ pool size (Table ​ (Table2), 2 ), which both control not only the NPQ capacity, but are further supposed to modify the membrane flexibility (Horton, 2014 ) and the structural arrangement of PSII supercomplexes (Ruban and Johnson, 2015 ). The high NPQ capacity of NatL plants was based on the known PsbS and Zx dependent quenching sites Q1 and Q2, while energy transfer from PSII to PSI was involved in the NPQ of HL plants (Table ​ (Table4). 4 ). The latter mechanism has recently been characterized in microalgae after exposure to extreme HL stress (Slavov et al., 2016 ). We speculate that such an energy spillover NPQ mechanism may become generally activated during exposure to constant HL conditions. However, the high NPQ capacity of both HL and NatL plants was accompanied by unstacking of thylakoid membranes (Figure ​ (Figure7). 7 ). Unstacking of the membranes is supposed to indispensable for a spillover mechanism to allow for the required contact of PSII and PSI (Slavov et al., 2016 ). Our data suggest that the structural flexibility of the thylakoid membrane provides the basis for a high NPQ capacity of plants, independent of the underlying mechanism. It remains to be elucidated, which factors determine and regulate this structural flexibility. Our data indicate that a reduced degree of grana stacking, an increased fraction of stroma exposed membranes, and a low lipid/protein ratio might be a prerequisite for the structural flexibility. The rapid reversibility of unstacking observed in NatL plants points to a possible role of the transthylakoid pH gradient or light-regulated ion fluxes in the regulation of the structural dynamics.

In conclusion, our work shows that NatL plants exhibit a number of striking features that allow for optimal light utilization, and underlines the importance of the use of plants grown under NatL conditions for studying light acclimation in plants.

Author contributions

PJ and TS wrote the manuscript, planned and designed the experiments. TS, SP, MM, and PD performed the experiments. All authors analyzed and interpreted the data; read and approved the final version of the manuscript.

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) to PJ (JA 665/9-1).

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We are indebted to Dr. Viviana Correa-Galvis (MPI Golm, Germany) for her generous help in statistical analysis of the data. We thank Dr. Mark Aurel Schöttler (MPI Golm, Germany) for his generous help in spectroscopic determination of the stoichiometries of PSII, PSI and Cyt b 6 /f. We are grateful to Dr. Alfred Holzwarth (MPI Mülheim a.d.Ruhr, Germany) for providing the facilities for ultrafast fluorescence measurements and data analysis. We thank Kirsten Hoffie and Sybille Freist (IPK Gatersleben, Germany) for technical assistance. The help of Helga Peisker (University of Bonn) with lipid measurements is especially acknowledged.

Supplementary material

The Supplementary Material for this article can be found online at: http://journal.frontiersin.org/article/10.3389/fpls.2017.00681/full#supplementary-material

• Adams W. W., III., Demmig-Adams B., Rosenstiel T. N., Brightwell A. K., Ebbert V. (2002). Photosynthesis and photoprotection in overwintering plants . Plant Biol. 4 , 545–557. 10.1055/s-2002-35434 [ CrossRef ] [ Google Scholar ]
• Adams W. W., III., Demmig-Adams B., Verhoeven A. S., Barker D. H. (1995b). ‘Photoinhibition’ during winter stress: involvement of sustained xanthophyll cycle-dependent energy dissipation . Aust. J. Plant Physiol. 22 , 261–276. 10.1071/PP9950261 [ CrossRef ] [ Google Scholar ]
• Adams W. W., III., Hoehn A., Demmig-Adams B. (1995a). Chilling temperatures and the xanthophyll cycle. A comparison of warm-grown and overwintering spinach . Aust. J. Plant Physiol. 22 , 75–85. 10.1071/PP9950075 [ CrossRef ] [ Google Scholar ]
• Ahn T. K., Avenson T. J., Ballottari M., Cheng Y. C., Niyogi K. K., Bassi R., et al.. (2008). Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein . Science 320 , 794–797. 10.1126/science.1154800 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Albanese P., Manfredi M., Meneghesso A., Marengo E., Saracco G., Barber J., et al.. (2016). Dynamic reorganization of photosystem II supercomplexes in response to variations in light intensities . Biochim. Biophys. Acta 1857 , 1651–1660. 10.1016/j.bbabio.2016.06.011 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Amarnath K., Zaks J., Park S. D., Niyogi K. K., Fleming G. R. (2012). Fluorescence lifetime snapshots reveal two rapidly reversible mechanisms of photoprotection in live cells of Chlamydomonas reinhardtii . Proc. Natl. Acad. Sci. U.S.A. 109 , 8405–8410. 10.1073/pnas.1205303109 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Anderson J. M. (1986). Photoregulation of the composition, function, and structure of thylakoid membranes . Annu. Rev. Plant Physiol. Plant Mol. Biol. 37 , 93–136. 10.1146/annurev.pp.37.060186.000521 [ CrossRef ] [ Google Scholar ]
• Anderson J. M., Goodchild D. J., Boardman N. K. (1973). Composition of photosystems and chloroplast structure in extreme shade plants . Biochim. Biophys. Acta 325 , 573–585. 10.1016/0005-2728(73)90217-x [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Arve L. E., Kruse O. M., Tanino K. K., Olsen J. E., Futsather C., Torre S. (2017). Daily changes in VPD during leaf development in high air humidity increase the stomatal responsiveness to darkness and dry air . J. Plant Physiol. 211 , 63–69. 10.1016/j.jplph.2016.12.011 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Austin J. R., Frost E., Vidi P. A., Kessler F., Staehelin L. A. (2006). Plastoglobules are lipoprotein subcompartments of the chloroplast that are permanently coupled to thylakoid membranes and contain biosynthetic enzymes . Plant Cell 18 , 1693–1703. 10.1105/tpc.105.039859 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Avenson T. J., Ahn T. K., Zigmantas D., Niyogi K. K., Li Z., Ballottari M., et al.. (2008). Zeaxanthin radical cation formation in minor light-harvesting complexes of higher plant antenna . J. Biol. Chem. 283 , 3550–3558. 10.1074/jbc.m705645200 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Bailey S., Horton P., Walters R. G. (2004). Acclimation of Arabidopsis thaliana to the light environment: the relationship between photosynthetic function and chloroplast composition . Planta 218 , 793–802. 10.1007/s00425-003-1158-5 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ballottari M., Dall'Osto L., Morosinotto T., Bassi R. (2007). Contrasting behavior of higher plant photosystem I and II antenna systems during acclimation . J. Biol. Chem. 282 , 8947–8958. 10.1074/jbc.m606417200 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Benson A. A., Wintermans J., Wiser R. (1959). Chloroplast lipids as carbohydrate reservoirs . Plant Physiol. 34 , 315–317. 10.1104/pp.34.3.315 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Berry J., Bjorkman O. (1980). Photosynthetic response and adaptation to temperature in higher plants . Annu. Rev. Plant Physiol. Plant Mol. Biol. 31 , 491–543. 10.1146/annurev.pp.31.060180.002423 [ CrossRef ] [ Google Scholar ]
• Björkman O., Holmgren P. (1963). Adaptability of photosynthetic apparatus to light intensity in ecotypes from exposed and shaded habitats . Physiol. Plant 16 , 889–914. 10.1111/j.1399-3054.1963.tb08366.x [ CrossRef ] [ Google Scholar ]
• Blázquez M. A., Ahn J. H., Weigel D. (2003). A thermosensory pathway controlling flowering time in Arabidopsis thaliana . Nat. Genet. 33 , 168–171. 10.1038/ng1085 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Boardman N. K. (1977). Comparative photosynthesis of sun and shade plants . Annu. Rev. Plant Physiol. Plant Mol. Biol. 28 , 355–377. 10.1146/annurev.pp.28.060177.002035 [ CrossRef ] [ Google Scholar ]
• Brugnoli E., Cona A., Lauteri M. (1994). Xanthophyll cycle components and capacitiy for non-radiative energy dissipation in sun and shade leaves of Ligustrum ovalifolium exposed to conditions limiting photosynthesis . Photosynth. Res. 41 , 451–463. 10.1007/BF02183047 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Correa-Galvis V., Poschmann G., Melzer M., Stühler K., Jahns P. (2016). PsbS interactions involved in the activation of energy dissipation in Arabidopsis . Nat. Plants 2 :15225. 10.1038/nplants.2015.225 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Daghma D. S., Kumlehn J., Melzer M. (2011). The use of cyanobacteria as filler in nitrocellulose capillaries improves ultrastructural preservation of immature barley pollen upon high pressure freezing . J. Microsc. 244 , 79–84. 10.1111/j.1365-2818.2011.03509.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Dall'Osto L., Caffarri S., Bassi R. (2005). A mechanism of nonphotochemical energy dissipation, independent from PsbS, revealed by a conformational change in the antenna protein CP26 . Plant Cell 17 , 1217–1232. 10.1105/tpc.104.030601 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Demmig B., Winter K., Krüger A., Czygan F.-C. (1987). Photoinhibition and zeaxanthin formation in intact leaves. A possible role of the xanthophyll cycle in the dissipation of excess light . Plant Physiol. 84 , 218–224. 10.1104/pp.84.2.218 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Demmig-Adams B., Adams W. W., III. (1996). Xanthophyll cycle and light stress in nature: uniform response to excess direct sunlight among higher plant species . Planta 198 , 460–470. 10.1007/BF00620064 [ CrossRef ] [ Google Scholar ]
• Demmig-Adams B., Ebbert V., Mellman D. L., Mueh K. E., Schaffer L., Funk C., et al. (2006). Modulation of PsbS and flexible vs sustained energy dissipation by light environment in different species . Physiol. Plant. 127 , 670–680. 10.1111/j.1399-3054.2006.00698.x [ CrossRef ] [ Google Scholar ]
• Demmig-Adams B., Muller O., Stewart J. J., Cohu C. M., Adams W. W., III. (2015). Chloroplast thylakoid structure in evergreen leaves employing strong thermal energy dissipation . J. Photochem. Photobiol. B 152 , 357–366. 10.1016/j.jphotobiol.2015.03.014 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Derks A., Schaven K., Bruce D. (2015). Diverse mechanisms for photoprotection in photosynthesis. Dynamic regulation of photosystem II excitation in response to rapid environmental change . Biochim. Biophys. Acta 1847 , 468–485. 10.1016/j.bbabio.2015.02.008 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ebbert V., Adams W. W., Mattoo A. K., Sokolenko A., Demmig-Adams B. (2005). Up-regulation of a photosystem II core protein phosphatase inhibitor and sustained D1 phosphorylation in zeaxanthin-retaining, photoinhibited needles of overwintering Douglas fir . Plant Cell Environ. 28 , 232–240. 10.1111/j.1365-3040.2004.01267.x [ CrossRef ] [ Google Scholar ]
• Falcone D. L., Ogas J. P., Somerville C. R. (2004). Regulation of membrane fatty acid composition by temperature in mutants of Arabidopsis with alterations in membrane lipid composition . BMC Plant Biol. 4 :17. 10.1186/1471-2229-4-17 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Färber A., Young A. J., Ruban A. V., Horton P., Jahns P. (1997). Dynamics of xanthophyll-cycle activity in different antenna subcomplexes in the photosynthetic membranes of higher plants: the relationship between zeaxanthin conversion and nonphotochemical fluorescence quenching . Plant Physiol. 115 , 1609–1618. 10.1104/pp.115.4.1609 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Gasulla F., vom Dorp K., Dombrink I., Zahringer U., Gisch N., Dormann P., et al.. (2013). The role of lipid metabolism in the acquisition of desiccation tolerance in Craterostigma plantagineum : a comparative approach . Plant J. 75 , 726–741. 10.1111/tpj.12241 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Genty B., Briantais J.-M., Baker N. R. (1989). The relationship between quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence . Biochim. Biophys. Acta 990 , 87–92. [ Google Scholar ]
• Goss R., Lepetit B. (2015). Biodiversity of NPQ . J. Plant Physiol. 172 , 13–32. 10.1016/j.jplph.2014.03.004 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Holt N. E., Zigmantas D., Valkunas L., Li X. P., Niyogi K. K., Fleming G. R. (2005). Carotenoid cation formation and the regulation of photosynthetic light harvesting . Science 307 , 433–436. 10.1126/science.1105833 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Holzwarth A. R., Miloslavina Y., Nilkens M., Jahns P. (2009). Identification of two quenching sites active in the regulation of photosynthetic light-harvesting studied by time-resolved fluorescence . Chem. Phys. Lett. 483 , 262–267. 10.1016/j.cplett.2009.10.085 [ CrossRef ] [ Google Scholar ]
• Horton P. (2014). Developments in research on non-photochemical fluorescence quenching: emergence of key ideas, theories and experimental approaches , in Non-Photochemical Quenching and Energy Dissipation in Plants, Algae and Cyanobacteria , eds Demmig-Adams B., Adams W. W., II, Garab G., Govindjee (Dordrecht: Springer; ), 73–95. [ Google Scholar ]
• Horton P., Ruban A. V., Walters R. G. (1996). Regulation of light harvesting in green plants . Annu. Rev. Plant Physiol. Plant Mol. Biol. 47 , 655–684. 10.1146/annurev.arplant.47.1.655 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Horton P., Wentworth M., Ruban A. (2005). Control of the light harvesting function of chloroplast membranes: the LHCII-aggregation model for non-photochemical quenching . FEBS Lett. 579 , 4201–4206. 10.1016/j.febslet.2005.07.003 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Jahns P., Holzwarth A. R. (2012). The role of the xanthophyll cycle and of lutein in photoprotection of photosystem II . Biochim. Biophys. Acta 1817 , 182–193. 10.1016/j.bbabio.2011.04.012 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Jahns P., Latowski D., Strzalka K. (2009). Mechanism and regulation of the violaxanthin cycle: the role of antenna proteins and membrane lipids . Biochim. Biophys. Acta 1787 , 3–14. 10.1016/j.bbabio.2008.09.013 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Jahns P., Miehe B. (1996). Kinetic correlation of recovery from photoinhibition and zeaxanthin epoxidation . Planta 198 , 202–210. 10.1007/BF00206245 [ CrossRef ] [ Google Scholar ]
• Kirchhoff H. (2014). Diffusion of molecules and macromolecules in thylakoid membranes . Biochim. Biophys. Acta 1837 , 495–502. 10.1016/j.bbabio.2013.11.003 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Kley J., Heil M., Muck A., Svatos A., Boland W. (2010). Isolating intact chloroplasts from small Arabidopsis samples for proteomic studies . Anal. Biochem. 398 , 198–202. 10.1016/j.ab.2009.11.016 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Klughammer C., Schreiber U. (1994). An improved method, using saturating light-pulses, for the determination of photosystem-I quantum yield via P700+ absorbency changes at 830 nm . Planta 192 , 261–268. 10.1007/BF01089043 [ CrossRef ] [ Google Scholar ]
• Kramer D. M., Johnson G., Kiirats O., Edwards G. E. (2004). New fluorescence parameters for the determination of Q(A) redox state and excitation energy fluxes . Photosynth. Res. 79 , 209–218. 10.1023/B:PRES.0000015391.99477.0d [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Krause G. H., Vernotte C., Briantais J.-M. (1982). Photoinduced quenching of chlorophyll fluorescence in intact chloroplasts and algae. Resolution into two components . Biochim. Biophys. Acta 679 , 116–124. 10.1016/0005-2728(82)90262-6 [ CrossRef ] [ Google Scholar ]
• Krause G. H., Jahns P. (2004). Non-photochemical energy dissipation determined by chlorophyll fluorescence quenching. Characterization and function , in Chlorophyll Fluorescence: A Signature of Photosynthesis, Advances in Photosynthesis and Respiration , eds Papageorgiou G. C., Govindjee (Dordrecht: Kluwer Academic Publishers; ), 463–495. [ Google Scholar ]
• Kyhse-Andersen J. (1984). Electroblotting of multiple gels - A simple apparatus without buffer tank for rapid transfer of proteins frompolyacrylamide to nitrocellulose . J. Biochem. Biophys. Methods 10 , 203–209. 10.1016/0165-022X(84)90040-X [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Laemmli U. K. (1970). Cleavage of structural proteins during the assembly of the head of bacteriophage T4 . Nature 227 , 680–685. 10.1038/227680a0 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Leong T. Y., Anderson J. M. (1984). Adaptation of the thylakoid membranes of pea chloroplasts to light intensities. 2. Regulation of electron transport capacities, electron carriers, coupling factor (CF1) activity and rates of photosynthesis . Photosynth. Res. 5 , 117–128. 10.1007/BF00028525 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Li X.-P., Björkman O., Shih C., Grossman A. R., Rosenquist M., Jansson S., et al.. (2000). A pigment-binding protein essential for regulation of photosynthetic light harvesting . Nature 403 , 391–395. 10.1038/35000131 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Li X. P., Gilmore A. M., Caffarri S., Bassi R., Golan T., Kramer D., et al.. (2004). Regulation of photosynthetic light harvesting involves intrathylakoid lumen pH sensing by the PsbS protein . J. Biol. Chem. 279 , 22866–22874. 10.1074/jbc.M402461200 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Li Z. R., Wakao S., Fischer B. B., Niyogi K. K. (2009). Sensing and responding to excess light . Annu. Rev. Plant Biol. 60 , 239–260. 10.1146/annurev.arplant.58.032806.103844 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Lichtenthaler H. (1968). Plastoglobuli and the fine structure of plastids . Endeavour 27 , 144–149. [ Google Scholar ]
• Lichtenthaler H. K., Buschmann C., Doll M., Fietz H. J., Bach T., Kozel U., et al.. (1981). Photosynthetic activity, chloroplast ultrastructure, and leaf characteristics of high-light and low-light plants and of sun and shade leaves . Photosynth. Res. 2 , 115–141. 10.1007/BF00028752 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Los D. A., Mironov K. S., Allakhverdiev S. I. (2013). Regulatory role of membrane fluidity in gene expression and physiological functions . Photosynth. Res. 116 , 489–509. 10.1007/s11120-013-9823-4 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Los D. A., Murata N. (2004). Membrane fluidity and its roles in the perception of environmental signals . Biochim. Biophys. Acta 1666 , 142–157. 10.1016/j.bbamem.2004.08.002 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ludlow M. M., Wilson G. L. (1971). Photosynthesis of tropical pasture plants. 2. Temperature and illuminance history . Aust. J. Biol. Sci. 24 , 1065–1075. 10.1071/BI9711065 [ CrossRef ] [ Google Scholar ]
• Malkin S., Armond P. A., Mooney H. A., Fork D. C. (1981). Photosystem II photosynthetic unit sizes from fluorescence induction in leaves–correlation to photosynthetic capacity . Plant Physiol. 67 , 570–579. 10.1104/pp.67.3.570 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Miloslavina Y., de Bianchi S., Dall'Osto L., Bassi R., Holzwarth A. R. (2011). Quenching in Arabidopsis thaliana mutants lacking monomeric antenna proteins of photosystem II . J. Biol. Chem. 286 , 36830–36840. 10.1074/jbc.M111.273227 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Miloslavina Y., Grouneva I., Lambrev P. H., Lepetit B., Goss R., Wilhelm C., et al.. (2009). Ultrafast fluorescence study on the location and mechanism of non-photochemical quenching in diatoms . Biochim. Biophys. Acta 1787 , 1189–1197. 10.1016/j.bbabio.2009.05.012 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Mishra Y., Jankanpaa H. J., Kiss A. Z., Funk C., Schroder W. P., Jansson S. (2012). Arabidopsis plants grown in the field and climate chambers significantly differ in leaf morphology and photosystem components . BMC Plant Biol. 12 :6. 10.1186/1471-2229-12-6 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Müller P., Li X. P., Niyogi K. K. (2001). Non-photochemical quenching. A response to excess light energy . Plant Physiol. 125 , 1558–1566. 10.1104/pp.125.4.1558 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Mullineaux C. W., Kirchhoff H. (2009). Role of lipids in the dynamics of thylakoid membranes , in Lipids in Photosynthesis Essential and Regulatory Function , eds Murata N., Wada H. (Dordrecht: Springer Science; ), 283–294. [ Google Scholar ]
• Nilkens M., Kress E., Lambrev P. H., Miloslavina Y., Müller M., Holzwarth A. R., et al.. (2010). Identification of a slowly inducible zeaxanthin-dependent component of non-photochemical quenching of chlorophyll fluorescence generated under steady state conditions in Arabidopsis . Biochim. Biophys. Acta 1797 , 466–475. 10.1016/j.bbabio.2010.01.001 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Park Y. I., Chow W. S., Anderson J. M., Hurry V. M. (1996). Differential susceptibility of Photosystem II to light stress in light-acclimated pea leaves depends on the capacity for photochemical and non-radiative dissipation of light . Plant Sci. 115 , 137–149. 10.1016/0168-9452(96)04339-7 [ CrossRef ] [ Google Scholar ]
• Quick W. P., Stitt M. (1989). An examination of factors contributing to non-photochemical quenching of chlorophyll fluorescence in barley leaves . Biochim. Biophys. Acta 977 , 287–296. 10.1016/s0005-2728(89)80082-9 [ CrossRef ] [ Google Scholar ]
• Reinhold C., Niczyporuk S., Beran K., Jahns P. (2008). Short-term down-regulation of zeaxanthin epoxidation in Arabidopsis thaliana in response to photo-oxidative stress conditions . Biochim. Biophys. Acta 1777 , 462–469. 10.1016/j.bbabio.2008.03.002 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Robert B., Horton P., Pascal A. A., Ruban A. V. (2004). Insights into the molecular dynamics of plant light-harvesting proteins in vivo . Trends Plant Sci. 9 , 385–390. 10.1016/j.tplants.2004.06.006 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Rottet S., Besagni C., Kessler F. (2015). The role of plastoglobules in thylakoid lipid remodeling during plant development . Biochim. Biophys. Acta 1847 , 889–899. 10.1016/j.bbabio.2015.02.002 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ruban A. V., Berera R., Ilioaia C., van Stokkum I. H., Kennis J. T., Pascal A. A., et al.. (2007). Identification of a mechanism of photoprotective energy dissipation in higher plants . Nature 450 , 575–578. 10.1038/nature06262 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ruban A. V., Johnson M. P. (2015). Visualizing the dynamic structure of the plant photosynthetic membrane . Nat. Plants 1 :15161. 10.1038/nplants.2015.161 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Ruban A. V., Johnson M. P., Duffy C. D. (2012). The photoprotective molecular switch in the photosystem II antenna . Biochim. Biophys. Acta 1817 , 167–181. 10.1016/j.bbabio.2011.04.007 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Sacharz J., Giovagnetti V., Ungerer P., Mastroianni G., Ruban A. V. (2017). The xanthophyll cycle affects reversible interactions between PsbS and light-harvesting complex II to control non-photochemical quenching . Nat. Plants 3 :16225 10.1038/nplants.2016.225 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Schoettler M. A., Toth S. Z. (2014). Photosynthetic complex stoichiometry dynamics in higher plants: environmental acclimation and photosynthetic flux control . Front. Plant Sci. 5 :188. 10.3389/fpls.2014.00188 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Slavov C., Schrameyer V., Reus M., Ralph P. J., Hill R., Buechel C., et al.. (2016). “Super-quenching” state protects Symbiodinium from thermal stress - Implications for coral bleaching . Biochim. Biophys. Acta 1857 , 840–847. 10.1016/j.bbabio.2016.02.002 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Song Y. H. (2016). The effect of fluctuations in photoperiod and ambient temperature on the timing of flowering: time to move on natural environmental conditions . Mol. Cells 39 , 715–721. 10.14348/molcells.2016.0237 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Stirbet A., Govindjee (2011). On the relation between the Kautsky effect (chlorophyll a fluorescence induction) and Photosystem II: basics and applications of the OJIP fluorescence transient . J. Photochem. Photobiol. B 104 , 236–257. 10.1016/j.jphotobiol.2010.12.010 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Takizawa K., Cruz J. A., Kanazawa A., Kramer D. M. (2007). The thylakoid proton motive force in vivo . Quantitative, non-invasive probes, energetics, and regulatory consequences of light-induced pmf . Biochim. Biophys. Acta 1767 , 1233–1244. 10.1016/j.bbabio.2007.07.006 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Tikkanen M., Mekala N. R., Aro E.-M. (2014). Photosystem II photoinhibition-repair cycle protects photosystem I from irreversible damage . Biochim. Biophys. Acta 1837 , 210–215. 10.1016/j.bbabio.2013.10.001 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• van Stokkum I. H., Larsen D. S., van Grondelle R. (2004). Global and target analysis of time-resolved spectra . Biochim. Biophys. Acta 1657 , 82–104. 10.1016/j.bbabio.2004.04.011 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Verhoeven A. S., Adams W. W. I., Demmig-Adams B. (1996). Close relationship between the state of the xanthophyll cycle pigments and photosystem II efficiency during recovery from winter stress . Physiol. Plant 96 , 567–576. 10.1111/j.1399-3054.1996.tb00228.x [ CrossRef ] [ Google Scholar ]
• Walters R. G., Horton P. (1991). Resolution of components of non-photochemical chlorophyll fluorescence quenching in barley leaves . Photosynth. Res. 27 , 121–133. 10.1007/BF00033251 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Welti R., Li W. Q., Li M. Y., Sang Y. M., Biesiada H., Zhou H. E., et al.. (2002). Profiling membrane lipids in plant stress responses–role of phospholipase D alpha in freezing-induced lipid changes in Arabidopsis . J. Biol. Chem. 277 , 31994–32002. 10.1074/jbc.M205375200 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Weston E., Thorogood K., Vinti G., Lopez-Juez E. (2000). Light quantity controls leaf-cell and chloroplast development in Arabidopsis thaliana wild type and blue-light-perception mutants . Planta 211 , 807–815. 10.1007/s004250000392 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Wild A. (1980). Phyiology of photosynthesis in higher plants–adaptation to light-intensity and light quality . Ber. Dtsch. Bot. Ges. 92 , 341–364. [ Google Scholar ]
• Wild A., Wolf G. (1980). The effect of different light intensities on the frequency and size of stomata, the size of cells, the number size and chlorophyll content of chloroplasts in the mesophyll and the guard-cells during the ontogeny of primary leaves of Sinapis alba . Z. Pflanzenphys. 97 , 325–342. 10.1016/s0044-328x(80)80006-7 [ CrossRef ] [ Google Scholar ]
• Yamori W. (2016). Photosynthetic response to fluctuating environments and photoprotective strategies under abiotic stress . J. Plant Res. 129 , 379–395. 10.1007/s10265-016-0816-1 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Zarter C. R., Adams W. W., Ebbert V., Adamska I., Jansson S., Demmig-Adams B. (2006a). Winter acclimation of PsbS and related proteins in the evergreen Arctostaphylos uva-ursi as influenced by altitude and light environment . Plant Cell Environ. 29 , 869–878. 10.1111/j.1365-3040.2005.01466.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Zarter C. R., Adams W. W., Ebbert V., Cuthbertson D. J., Adamska I., Demmig-Adams B. (2006b). Winter down-regulation of intrinsic photosynthetic capacity coupled with up-regulation of Elip-like proteins and persistent energy dissipation in a subalpine forest . New Phytol. 172 , 272–282. 10.1111/j.1469-8137.2006.01815.x [ PubMed ] [ CrossRef ] [ Google Scholar ]

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here .

Loading metrics

Open Access

Peer-reviewed

Research Article

The effect of light quality on plant physiology, photosynthetic, and stress response in Arabidopsis thaliana leaves

Roles Conceptualization, Data curation, Formal analysis, Methodology, Visualization, Writing – original draft

* E-mail: [email protected] (ML); [email protected] (NY)

Affiliation Department of Bioresource Engineering, McGill University–Macdonald Campus, Sainte-Anne-de-Bellevue, Quebec, Canada

Roles Methodology

Affiliation Department of Plant Science, McGill University–Macdonald Campus, Sainte-Anne-de-Bellevue, Quebec, Canada

Roles Writing – review & editing

Roles Resources

Roles Conceptualization, Funding acquisition, Investigation, Project administration, Resources, Supervision, Writing – original draft

• Nafiseh Yavari, 
• Rajiv Tripathi, 
• Bo-Sen Wu, 
• Sarah MacPherson, 
• Jaswinder Singh, 
• Mark Lefsrud

• Published: March 4, 2021
• https://doi.org/10.1371/journal.pone.0247380
• Reader Comments

The impacts of wavelengths in 500–600 nm on plant response and their underlying mechanisms remain elusive and required further investigation. Here, we investigated the effect of light quality on leaf area growth, biomass, pigments content, and net photosynthetic rate (Pn) across three Arabidopsis thaliana accessions, along with changes in transcription, photosynthates content, and antioxidative enzyme activity. Eleven-leaves plants were treated with BL; 450 nm, AL; 595 nm, RL; 650 nm, and FL; 400–700 nm as control. RL significantly increased leaf area growth, biomass, and promoted Pn. BL increased leaf area growth, carotenoid and anthocyanin content. AL significantly reduced leaf area growth and biomass, while Pn remained unaffected. Petiole elongation was further observed across accessions under AL. To explore the underlying mechanisms under AL, expression of key marker genes involved in light-responsive photosynthetic reaction, enzymatic activity of antioxidants, and content of photosynthates were monitored in Col-0 under AL, RL (as contrast), and FL (as control). AL induced transcription of GSH2 and PSBA , while downregulated NPQ1 and FNR2 . Photosynthates, including proteins and starches, showed lower content under AL. SOD and APX showed enhanced enzymatic activity under AL. These results provide insight into physiological and photosynthetic responses to light quality, in addition to identifying putative protective-mechanisms that may be induced to cope with lighting-stress in order to enhance plant stress tolerance.

Citation: Yavari N, Tripathi R, Wu B-S, MacPherson S, Singh J, Lefsrud M (2021) The effect of light quality on plant physiology, photosynthetic, and stress response in Arabidopsis thaliana leaves. PLoS ONE 16(3): e0247380. https://doi.org/10.1371/journal.pone.0247380

Editor: Keqiang Wu, National Taiwan University, TAIWAN

Received: August 31, 2020; Accepted: December 13, 2020; Published: March 4, 2021

Copyright: © 2021 Yavari et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: This work was supported by the “Natural Sciences and Engineering Research Council of Canada (NSERC)”. The specific grant number is RGPIN 355743-13, CRDPJ418919-11. It is “all” the funding and/or financial sources of support (whether external and/or internal to our organization) that were received during this study. And there was no additional external and/or internal funding received for this study. ML is the author, who received this award. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Introduction

Among various environmental factors, light is one of the most important variables affecting photosynthesis as well as plant growth and development [ 1 ]. Plants require light not only as an energy source but also as a clue to adjust their development to environmental conditions. During photosynthesis, absorbed energy is transferred to the photosynthetic apparatus, which is comprised of Photosystem I (PSI), Photosystem II (PSII), electron transport ‬carriers (cytochrome b6f (cytb6f), plastoquinone (PQ), plastocyanin (PC)), and ATP synthase. The light-responsive photosynthetic process is driven by the released electrons through the water-splitting reaction on the PSII side, followed by NADP + reduction to NADPH, and proton flow into the lumen in order to generate ATP. Generated NADPH and ATP serve as an energy source for the carbon fixation process [ 2 ].‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬

‬‬‬‬‬‬‬‬‬‬‬‬ Both quality and quantity of incident light can have drastic impacts on photosynthetic activity and photosystem adaption to changing light quality [ 3 , 4 ]. Earlier studies on photosynthetic activity reported that photosynthesis is a wavelength-dependent response, in which amber light (AL; 595 nm) induces higher photosynthetic rates than blue light (BL; 450 nm) or red light (RL; 650 nm) [ 3 , 5 , 6 ]. These studies have become the foundation for our plant lighting research as light emitting diodes (LEDs) are proven to be ‬an ‬optimal and effective ‬tool to study the effect of ‬‬‬‬wavelength on plant physiological and biochemical responses [ 7 – 10 ]. Prior research has demonstrated that the wavelength range from 430–500 nm is effective at simulating pigmentation, metabolism of secondary metabolites, photosynthetic function, and development of chloroplasts [ 11 – 14 ]. The wavelength range of 640–670 nm was found effective in promoting photosynthetic activity, plant biomass and leaf area growth [ 3 , 15 ] while playing critically important roles in the development of photosynthetic apparatus, net photosynthetic rate (Pn) and primary metabolism [ 12 , 16 ]. Growing research on the wavelength range 500–600 nm have highlighted its important physiological and morphological impact on growth, chlorophyll content, and photosynthetic function [ 8 , 17 – 19 ]. However, conflicting results on the impact of AL were reported [ 3 , 20 ]. Although AL results in high photosynthetic activity, poor plant growth responses such as elongation and growth suppression have been reported [ 20 , 21 ], and this underlying mechanism remains unknown. In addition to this, AL is weakly absorbed by the photosynthetic pigments [ 22 ]. At the current state, further investigation of AL impact is required to better understand the photoactivity of the photosystems.‬ ‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬

Recent studies reported that light quality and quantity can have drastic impacts on imbalanced excitation of either PSII or PSI, resulting in energy imbalance between photosystems and triggering stoichiometric adjustments of photosynthetic complexes [ 23 , 24 ]. This imbalance between the two photosystems can result in generation of harmful reactive intermediates, mainly reactive oxygen species (ROS) [ 25 , 26 ]. Generation of ROS can result in oxidative damage to the chloroplasts, leading to photosystem photo-inhibition that strongly limits plant growth [ 27 ].‬‬‬‬ To maintain steady state photosynthetic efficiency and prevent ROS accumulation, plants activate the buffering mechanisms, including cyclic photosynthetic electron flow (CEF) and non-photochemical quenching (NPQ) [ 28 , 29 ]. To scavenge ROS, plants further stimulate antioxidative mechanisms via enhanced activity of associated enzymes such as glutathione synthetase (GSH), ascorbate peroxidase (APX), and superoxide dismutase (SOD) [ 30 ]. These studies and their findings allow us to understand the impact of light within photosystems; however, the wavelength that can induce such stress responses and their physiological consequence on plants remain poorly studied.

Therefore, to better understand the effect of light quality on plant growth and photosynthetic performance, we studied three narrow-wavelength LEDs of blue light (BL; 450 nm), amber light (AL; 595 nm), and red light (RL; 650 nm), and compared them with fluorescent light (FL; 400–700) as the control. We chose light quality of BL and RL as leaf pigments have absorption peaks at these wavelengths [ 31 ]. AL was chosen due to the conflicting results between high photosynthetic activity and poor plant growth responses [ 3 , 5 ]. Furthermore, to assess whether light quality-induced changes in plant growth and photosynthesis are mediated by the genotype, we investigated the light quality response in three A . thaliana accessions Col-0, Est-1, and C24. These accessions show different geographical distributions and hence are adopted to different environments [ 32 – 34 ]. Congruently, they show a high degree of divergence in their photosynthetic response to the light environment [ 35 , 36 ]‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬. Two experiments were designed to‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬ ‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬assess the impact of light quality on the plant. First, we investigated the physiological and photosynthetic response of A . thaliana to BL, AL, and RL lights compared it to FL by measuring leaf area growth, biomass content, Pn, and pigments content. Second, we tested whether changes in plant response to light quality is genotype specific by conducting the experiments across three A . thaliana accessions. Third, we investigated the potential induction of stress responses under AL by testing whether there are light quality-specific changes in the expression of marker genes involved in light-responsive photosynthetic process and enzymatic activity of antioxidants, as well as photosynthates content. Our findings expand the current understanding on physiological and photosynthetic responses of plants to light quality, in addition to identifying putative protective-mechanisms that may be induced to cope with lighting-stress in order to enhance plant stress tolerance.

Materials and methods

Plant materials and growth condition.

Seeds of A . thaliana accessions Col-0, Est-1, and C24 were obtained from the Arabidopsis Biological Resource Center (ABRC; Columbus, OH, US). Seeds were placed in rockwool cubes (Grodan A/S, DK-2640, Hedehusene, Denmark) and incubated at 4°C for 2 days. White broad-spectrum light (FL; 4200 K, F72T8CW, Osram Sylvania, MA, US) were used as light sources for seed germination. Seedlings were hydroponically grown under FL for 21 days with the environmental condition of 24 h photoperiod, 23°C, 50% relative humidity, and ambient CO 2 in a growth chamber (TC30, Conviron, Winnipeg, MB, Canada). Seed density was adjusted to limit treated plants from shadowing each other. FL was placed over the plant-growing surface area (49 cm × 95 cm) at a low photosynthetic photon flux density (PPFD) of 69 to 71 μmol·m -2 ·sec -1 . PPFD was measured at the conjunction of a grid (square area 3 cm 2 ) placed over the growing area. After 21 days, plants formed rosettes with nine (C24) and eleven (Col-0 and Est-1) leaves. To reach the same growth stage as Col-0 and Est-1 plants, C24 plants were allowed to grow for 23 days [ 37 ]. Fresh half-strength Hoagland nutrient solution [ 38 ] was provided every other day.

Light treatment

After day 21 (Col-0 and Est-1) or 23 (C24), plants were transferred to their respective light treatment for 5 days, each with the same environmental conditions: 24 h photoperiod, 23°C, 50% relative humidity, and ambient CO 2 . 21-day old plants were randomly divided into four experimental groups and received treatments using light emitting diodes (LED) (VanqLED, Shenzhen, China) of BL (peak wavelength: 450 nm), AL (peak wavelength: 595 nm), and RL (peak wavelength: 650 nm). The fourth group was treated with FL (400–700 nm), as the control. The light spectra and PPFD were monitored daily by using a PS-300 spectroradiometer (Apogee, Logan, UT, US). PPFD was maintained at 69 to 71 μmol·m -2 ·sec -1 throughout the whole plant growth period. Fresh half-strength Hoagland nutrient solution [ 38 ] was provided every other day. Biological replicates were grown at different time points under the same environmental settings.

Physical and biochemical analyses

Leaf area growth determination..

Three plants per biological replicate were randomly selected for each measurement. Leaves from the selected plants were collected for the determination after treatment (5 days). Digital images of leaves were taken with a window size of 640 x 480 pixels and a camera-object distance of approximately 80 cm. The digital images were next used to determine leaf area growth using Image J software with default settings (Bethesda, MD, US), as described previously [ 39 ].

Biomass content determination.

Three plants per biological replicate were randomly selected for each determination. Leaf samples from the selected plants were collected for the dry mass determination before (0 h) and after treatment (5 days). Leaves were dried at 80°C for 2 days until a constant mass was achieved (less than < 5% mass difference over a 2 h period).

Pigment content determination.

Five plants per biological replicate were randomly selected for each assay. Leaf samples from the selected plants were collected for the determination after treatment (5 days). Methods and equations described by [ 40 – 42 ] were used to estimate the content of chlorophyll (Chl a and Chl b), carotenoids, and anthocyanin, respectively. Briefly, chlorophylls and carotenoids were extracted with 5 ml of 80% acetone at 4°C overnight, before centrifugation at 13,000 g for 5 min. Total anthocyanins were determined by extracting with 5 ml 80% methanol containing 1% HCl solvent at 4°C overnight, before centrifugation at 13,000 g for 5 min. The absorbance of the extraction solution was determined for Chl a (664 nm), Chl b (647 nm), carotenoids (440 nm), and anthocyanins (530 nm and 657 nm) using a UV–VIS spectrophotometer (UV-180, Shimadzu, Japan).

Net photosynthetic rate determination

Net photosynthetic rate was monitored before (0 h) and after treatment (5 days) using the LI-6400XT Portable Photosynthesis System (LI-COR Biosciences, Lincoln, NE, US) equipped with a 6400–17 Whole Plant Arabidopsis Chamber (LI-COR Biosciences). To reduce potential measurement errors, three plants were grouped as a single sample for determinations [ 43 ]. To avoid mismatch between the light quality used by the LI-6400XT Portable Photosynthetic System, and the LED lights used for the treatments [ 44 ], measurements were taken inside the controlled-chamber, in which whole plants (still embedded in rockwool) were placed and illuminated with LEDs. As a precaution, parafilm was placed on top of the rockwool cube to maintain moisture within the root zone while measurements were recorded. The environmental conditions of the chamber were set as: 400 ppm CO 2 , 50% relative humidity, 23°C, and 400 μl min -1 flow rate. Each measurement was taken over 20 min, including 5 min in the dark and 10–15 min under a light treatment at 69–71 μmol·m -2 ·sec -1 . A stable Pn reading was reached 10 min after illumination. Leaf area growth was determined to normalize Pn per unit leaf area growth. Measurements for three replicates (three plants per replicate, three replicates per treatment) were performed.

Photosynthate content determination

Previous studies have reported that the diurnal cycle and developmental stage of plants, along with the stress response can affect the plant metabolism [ 45 , 46 ]. Thus, we performed a time course assessment of 0, 1, 3, 5, and 7 days to determine the content of leaf photosynthates (proteins, starches, and lipids). Five plants per biological replicate were randomly selected for each measurement. Leaf samples from selected plants were collected for the determination prior (0 h) and after light treatments (1, 3, 5, and 7 days). Samples were immediately frozen in liquid nitrogen and stored at -80 ∘ C, before they were used for determination. Protein : Total protein content was measured using the Pierce™ BCA Protein Assay Kit (Thermo Fisher Scientific, Rockford, IL, USA). As a standard, the absorbance of the bovine serum albumin was determined at UV/Vis: λ max 562 nm. Starch : A previously described method [ 47 ] was used to estimate total starch content. Lipids : Previously described methods [ 48 , 49 ] were used (with minor modifications) to estimate the total lipid content. Briefly, each sample was homogenized with (CHCl 3 /MeOH, 70:30 v/v), before centrifuged at 1000 rpm for 5 min. The collected supernatant was incubated for 30 min at 70°C in a boiling water bath. Next, (H 2 SO 4 : 1 ml) was added and heated for 20 min. Following 2 min cooling on ice, (H 3 PO 4 : 1.5 ml) was added and incubated for 10 min until a pink color developed.

Antioxidative enzyme activity estimation

Five plants per biological replicate were randomly selected for each measurement. Leaf samples from selected plants were collected for the determination after treatment (5 days). Samples were immediately frozen in liquid nitrogen and stored at -80 ∘ C, before they were used for determination. Methods described by [ 50 , 51 ] were used to monitor the activity of SOD and APX antioxidative enzymes, respectively. Enzymatic activity was measured for 5 min at room temperature. The protein content in the supernatant was determined by the Pierce™ BCA Protein Assay Kit. The activity of SOD and APX was expressed as unit min −1 mg −1 protein.

Gene expression analysis

Cdna synthesis..

Changes in transcription of the interested genes were analyzed in A . thaliana Col-0 treated for 24 h under AL, RL, and FL. Leaf samples from selected plants were collected for the determination prior to treatment (0 h) and after treatment (2 h, 4 h, and 24 h). Samples were immediately frozen in liquid nitrogen and stored at -80 ∘ C, before they were used for determination. Four biological replicates were examined. For each biological replicate, five A . thaliana plants were selected, and their leaves were pooled together to represent a biological replicate. Plants in each biological replicate were grown independently, and at different times. Total RNA was extracted from (100 mg) leaves using the Sigma Spectrum Plant Total RNA Kit (STRN50; Sigma, Seelze, Germany) according to the manufacturer’s protocol. A total of (2 μg) RNA per sample was treated with amplification grade DNase I (Invitrogen, Carlsbad, CA, USA) to remove any traces of genomic DNA contamination. RNA concentrations were measured before and after DNase I digestion with a NanoDrop ND-1000 UV-Vis spectrophotometer (NanoDrop Technologies, Wilmington, Delware, USA). The cDNA was synthesized using AffinityScript QPCR cDNA Synthesis Kit (Agilent, Tech., Santa Clara, USA).

Primer design.

Primers for genes of interest ( S1 Table ) were designed using IDT software ( https://www.idtdna.com/calc/analyzer ) with the following criteria: Tm of 58–60°C and PCR amplicon lengths of 70 to 120 bp, yielding primer sequences 20 to 25 nucleotides in length with G-C contents of 40% to 50%. Specificity of the resulting primer pair sequences was examined using Arabidopsis transcript database with TAIR BLAST ( http://www.arabidopsis.org/Blast/ ). Specificity of the primer amplicons was further confirmed by melting-curve analysis (30 amplification cycles by PCR and subsequent gel-electrophoretic analysis). Primer amplicons were resolved on (agarose gels, 2% w/v) run at 110 V in Tris-borate/EDTA buffer, along with a 1Kb + DNA-standard ladder (Invitrogen, Carlsbad, CA, USA).

Quantitative real time-PCR (qRT-PCR) analysis.

Real-time qRT-PCR was performed with a MX3000P qPCR System (Agilent, Tech., Santa Clara, CA, USA) using three biological and two technical replicates, as described previously [ 52 ]. Relative expression was conducted following the manufacturer’s recommendations with two reference genes gamma tonoplast intrinsic protein 2 ( TIP2 ; AT3g26520) and actin 2 ( ACT2 ; AT3g18780) and the Brilliant III SYBR Green QPCR master mix (Agilent, Tech., Santa Clara, CA, USA). Amplification was performed in a (20 μL) reaction mixture containing (160 nmol) for each primer, 1x Brilliant III SYBR Green QPCR master mix, (15μM) ROX reference dye, and (0.3 μL) of cDNA template. Amplification conditions were 95°C for 10 min (hot start), followed by 40 cycles at 94°C for 30 s, 60°C for 30 s, and 72°C for 30 s. Fluorescence readings were taken at 72°C, at the end of the elongation cycle.

Data analysis.

Ct values were calculated with CFX-Manager and MX-3000P software. Relative expression changes (delta-delta Ct) were calculated according to [ 53 ] using A . thaliana TIP2 (AT3g26520) and ACT2 (AT3g18780) as reference genes. To avoid multiple testing, the p-values were only considered for 0 h with 24 h (a total of 12 genes and two light conditions). A gene was considered differentially expressed if p < 0.05 and the fold change pattern at 24 h was consistent with those observed at 2 and 4 h.

Statistical analysis

Differences between light treatments were tested using the two-tailed Student’s t-test. A two-way ANOVA was used to assess the effects of accession and different light treatments on leaf area growth, biomass content, Pn value, and pigments content. We observed similar patterns using the non-parametric tests of Wilcoxon-Mann-Whitney and Kruskal-Wallis tests (data not shown). ‬

Effect of light quality and natural genotype variation on leaf area growth, biomass content, net photosynthetic rate, and pigment content in A . thaliana

To assess the effect of light quality, 21-days-old plants (11 leave plants) of three A . thaliana accessions Col-0, Est-1, and C24 were randomly divided into groups and treated under narrow-spectrum light (BL, AL, and RL), along with FL as control (baseline), for 5 days at approximately 70 μmol m -2 sec -1 ( Fig 1A and 1B ). Summary of light quantity compositions emitted from FL and LEDs light sources are shown in Table 1 . After 5 days of narrow-spectrum light treatments, leaf area growth, leaf biomass (dry mass), net photosynthetic rate, and pigment contents were measured across three A . thaliana accessions and compared with the baseline FL treatment ( Fig 1C–1E and Table 2 ).

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

(A) Light emission spectra of LED light sources and FL. (B) Eleven-leaves stage A . thaliana accessions Col-0, Est-1, and C24 were grown hydroponically and treated for 5 days under narrow-spectrum BL, AL, and RL lights, as well as FL as control. (C) Leaf area growth. (D) Leaf biomass (dry mass). (E) Net photosynthetic rate (Pn) measured at 69–71 μmol m -2 sec -1 . Data are expressed as mean values ± standard deviation (n = 3). Statistical analysis was performed against FL using a two-tailed Student’s t-test (n.s.: not statistically significant; *: P < 0.05; **: P < 0.01).

https://doi.org/10.1371/journal.pone.0247380.g001

https://doi.org/10.1371/journal.pone.0247380.t001

https://doi.org/10.1371/journal.pone.0247380.t002

Under RL, the leaf area growth was significantly increased across accessions ( P < 0.05; Fig 1C ). Under BL, leaf area growth was significantly increased in C24 and Col-0 ( P < 0.05; Fig 2C ), but the increase in the leaf area growth was not significant in Est-1. Under AL, leaf area growth showed a severe reduction in Col-0 and C24 ( P < 0.05; Fig 1C ), while Al showed no change in Est-1. Petioles were noticeably elongated under AL ( Fig 1B ).

https://doi.org/10.1371/journal.pone.0247380.g002

The leaf biomass significantly increased under RL across the three accessions ( P < 0.05; Fig 1D ). Under BL, the leaf biomass was significantly decreased in Est-1 and C24 but increased in Col-0 ( P < 0.01; Fig 1D ). Under AL, the leaf biomass was significantly lower in Col-0 and C24 ( P < 0.01), while it showed no change in Est-1 ( Fig 1D ).

As for the net photosynthetic rates (Pn), it significantly increased under RL across the accessions ( P < 0.05; Fig 1E ). In contrast, there was no significant difference in Pn under AL ( Fig 1E ). Under BL, Pn significantly increased in Col-0 and Est-1 ( P < 0.05; Fig 1E ) but remained unchanged in C24.

There was no significant difference in contents of chlorophyll a (Chl a) and chlorophyll b (Chl b) in Col-0 and C24 under the light quality of BL, AL, and RL ( Table 2 ). In contrast, Chl a content significantly increased in Est-1 under RL ( P < 0.05; Table 2 ). Across accessions, Chl a: b content significantly increased, remained unchanged, and decreased under RL, BL, and AL, respectively ( Table 2 ). Moreover, there was no significant difference in carotenoid and anthocyanin contents across the accessions under AL and RL. However, BL significantly stimulated carotenoids content in Est-1 and Col-0 ( P < 0.05; Table 2 ). Additionally, anthocyanins content significantly increased under BL in Est-1 and C24 ( P < 0.01; Table 2 ).

The two-way ANOVA analysis indicated significant effects of the light treatments for the determined parameters, except Chl b. Also, the interaction between light treatments and genotype was significant for leaf area growth and leaf biomass ( P < 0.01; Table 3 ).

https://doi.org/10.1371/journal.pone.0247380.t003

Changes in transcription of photosynthetic marker genes, content of photosynthates, and activity of antioxidant in A . thaliana Col-0 under AL and RL

The severe reduction in leaf area growth and biomass, along with unchanged levels of Pn in Col-0 and C24 under AL suggested that amber light has mismatched effects on photosynthetic activity and photomorphology. Further to this, although chlorophyll contents under AL were 10–20% lower than the FL, both light treatments triggered similar photosynthetic activity, which implies that amber light has unidentified mechanisms in the photosynthetic process. To identify the mechanisms that amber light triggers within plants, we next explored transcriptional changes in marker genes associated with the photosynthetic light reaction and photo-protective mechanisms, photosynthates content and antioxidant enzymatic activity in Col-0 under AL ( Fig 2 ). Among three accession, Accession Col-0 was chosen for the transcription analysis, as it is the most common A . thaliana accession in conducting biological analysis. In addition to AL and FL (as control), changes were investigated under RL, as RL-treated plants showed opposing changes in leaf physiological phenotypes compared to AL.

Gene expression analysis indicated a significant increase in transcription level of ATP synthase gamma chain 1 ( ATPC1 ;member of ATP synthase complex) and proton gradient regulation Like 1 ( PGRL1B ;member of CET complex), after 24 h treatment under AL ( P < 0.05; Fig 3B ). ATPC1 transcription significantly increased after 24 h treatment under RL ( P < 0.05; Fig 3B ). No significant difference, after 24 h treatment, was observed in the transcription level of the selected marker genes associated with linear photosynthetic electron transfer (i.e., ferredoxin-2 ( Fd2) , plastocyanin (PETE1) , and cytochrome b6f complex ( PETC ) under both AL and RL ( Fig 3B ). After the 24 h treatment, transcription of ferredoxin-NADP+-oxidoreductase (FNR2) was significantly decreased under AL ( P < 0.05; Fig 3B ), while it remained unchanged under RL ( Fig 3B ). The transcription level of ribulose bisphosphate carboxylase small chain (RBCS1A) was significantly reduced at 2 h and 4 h treatment under both AL and RL ( P < 0.05; Fig 3B ). The RBCS1A transcription level significantly was downregulated under AL ( P < 0.05; Fig 3B ). However, RBCS1A transcription level recovered after the 24 h treatment under RL ( Fig 3B ).

(A) Genes of interest are highlighted in green. (B) Transcription of genes implicated in the light-responsive photosynthetic process that is located within the thylakoid membrane. A time course assessment prior to treatment (0 h), and after treatment (2, 4, and 24 h) of AL and RL was performed, compared to FL. Four biological replicates were examined. For each biological replicate, five A . thaliana plants were selected, and their leaves were pooled together to represent a biological replicate. Plants in each biological replicate were grown independently, and at different time.

https://doi.org/10.1371/journal.pone.0247380.g003

All data were normalized to the housekeeping genes; gamma tonoplast intrinsic protein 2 ( TIP2 ; AT3g26520) and actin 2 ( ACT2 ; AT3g18780). Red borders represent significant changes in expression ( P < 0.05). Studied genes include: ATP synthase gamma chain 1, ATPC1 (AT4g04640); fatty acid desaturase 6, FAD6 (AT4g30950); ferredoxin-2, Fd2 (AT1g60950); ferredoxin-NADP+-oxidoreductase, FNR2 (AT1g20020); (Fdx)-thioredoxin (Trx)-reductase, FTRB (AT2g04700); glutathione synthetase, GSH2 (AT5g27380); PSII nonphotochemical quenching, NPQ1 (AT1g08550); cytochrome b6f complex (Cyt b6f), PETC (AT4g03280); plastocyanin, PETE1 (AT1g76100); proton gradient regulation Like 1, PGRL1B (AT4g11960); photosystem II protein D1, PSBA (ATCG00020) and ribulose bisphosphate carboxylase small chain, RBCS1A (AT1g67090).

To confirm changes in the ATP synthase and CET complex under AL, we leveraged available proteomics data where eleven-leaves plants of A . thaliana Col-0 were grown under AL and RL for 5 days. Consistent with the observed transcriptomic data, a significant increase in the level of protein abundance was observed for both CET complex ( P < 1.3 x 10 −12 ; S1A Fig ) and ATP synthase ( P < 2 x 10 −4 ; S1B Fig ) under AL compared to RL.

Regulation patterns of PSBA , NPQ1 , GSH2 and FAD6 transcripts in A . thaliana Col-0 under AL and RL

The transcription level of photosystem II protein D1 ( PSBA) was significantly upregulated at 4 h and 24 h treatment under RL ( P < 0.05; Fig 3B ). Under AL, the transcription level of PBSA showed a similar increase after the 4 h treatment ( P < 0.05; Fig 3B ); However, its transcription level was reduced to a comparable level with FL after the 24 h treatment under AL. After the 24 h treatment, the transcription level of PSII nonphotochemical quenching (NPQ1) was significantly downregulated under AL ( P < 0.05; Fig 3B ), while it remained steady under RL. Between the 2 h and 4 h treatment, the transcription level of GSH2 gradually increased under both AL and RL ( P < 0.05; Fig 3B ) but reduced to a comparable level with FL after the 24 h treatment under RL. No significant difference was observed in the transcription level of fatty acid desaturase 6 ( FAD6) after the 24 h treatment under either AL or RL ( Fig 3B ).

Photosynthates content in A . thaliana Col-0 under AL and RL

Photosynthates accumulation was probed in Col-0 treated under AL, RL, and FL. Total lipid, protein and starch were measured at days 0, 1, 3, 5, and 7 ( Fig 4 ). The lipid content gradually increased under AL and RL ( P < 0.05; Fig 4A ). The content level of proteins and starches increased under RL but decreased under AL ( P < 0.05; Fig 4B and 4C ).

(A) Lipid; (B) Protein; (C) Starch. Data are expressed as mean values ± standard deviation (n = 5). Statistical analysis was performed against FL using a two-tailed Student’s t-test.

https://doi.org/10.1371/journal.pone.0247380.g004

Antioxidative enzyme activity in A . thaliana Col-0 under AL and RL

We examined the antioxidative activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzymes in Col-0 treated under AL, RL, and FL ( Fig 5 ). After the 24 h treatments, activity of both antioxidants was significantly increased under AL ( P < 0.05; Fig 5 ), while no significant changes were observed for either of these enzymes when plants were treated under RL.

(A) Superoxide dismutase (SOD) activity. One unit of SOD activity was defined as the amount of enzyme required to result in a 50% inhibition of the rate of reduction at 550 nm in 1 min. (B) Ascorbate peroxidase (APX) activity. One unit of APX activity was defined as the amount of enzyme required to oxidize 1 μmol of ascorbate at 290 nm in 1 min. Enzymatic activity was measured for 5 min at room temperature and data are expressed as mean values ± standard deviation (n = 5). Statistical analysis was performed against FL using a two-tailed Student’s t-test (n.s., not statistically significant; *, P < 0.05; **, P < 0.01).

https://doi.org/10.1371/journal.pone.0247380.g005

In this work, we investigated the impact of light quality BL, AL, and RL on leaf growth and photosynthetic response across three A . thaliana accessions Col-0, Est-1, and C24. The analyses clearly demonstrate the significant impact of light quality on leaf area growth, biomass content, and pigments accumulation (chlorophylls, carotenoid, and anthocyanin). The results indicate that light quality significantly influences Pn across accessions, consistent with the reported results that leaf photosynthetic reaction is wavelength-dependent in higher plants [ 54 ].

Importance of geographic habitats on light quality response of leaf growth and biomass

The selected accessions Col-0, Est-1, and C24 have different geographic habitats; C24 originated from a part of Europe (Portugal), Est-1 from Northern Asia (Russia), and Col-0 from United States (Columbia). Therefore, we took into account differences in geographical range for these accessions resulted in a high degree of divergence in photosynthetic characteristics to light [ 35 ]. The most extreme responder in leaf area growth and leaf biomass analyses was Est-1 from Russia. It is worth pointing out that the two Col-0 and C24 accessions highlighted here as weak responders, they elongated very quickly under AL and thus may not be true candidates for weak responders. Previous studies have found negative correlations between hypocotyl height and latitude of accession origin in European Arabidopsis accessions [ 55 , 56 ], suggesting that this natural variation in light sensitivity could be a result of adaptation to the north-south gradient in ambient light intensity.

The results of the study described here emphasize the strength of explicitly incorporating LxG interactions into the leaf area growth and leaf biomass content across the accessions. Importantly, as further elaborated below, the genotype-specific responses in leaf area growth and biomass content were observed exclusively under AL and BL, while the three accessions exhibited similar patterns of changes under RL. Our findings are consistent with previous reports on different accessions and light quality treatments, and underscores the importance of considering the natural habitat effect in characterizing the impact of light quality on leaves [ 57 ].

Leaf development varied between accessions such that the overall dynamic of growth and biomass were different. For example, we took efforts in synchronizing leaf growth stage in the accessions, resulting in the C24 plants being grow for 23 days to reach the same leaf stages of the plant. Some of the observed variation in leaf growth response could be simply a manifestation of the different time-course between accessions. These differences between accession can be significant and have the potential to enhance our understanding of the ecological role of specific adaptations.

Findings on BL supports its role on activation of protective pigments

BL induced higher leaf area growth across three accessions. However, its impact on biomass production is accession-dependent, and may be caused by accessory pigment accumulation (anthocyanins). Under BL, only Col-0 showed an increase in biomass, as opposed to Est-1 and C24, which showed a decrease in biomass. It was observed that BL induced a significantly higher concentration of anthocyanins in Est-1 and C24 than Col-0. These results imply that the impact of wavelength on accessory pigment accumulation is accession-dependent, and that this difference in accessory pigment accumulation consequently leads to differences in biomass production across accessions. Anthocyanin is a photo-protective pigment, which protects plant and its chloroplast membrane by absorbing blue light and against photo-oxidation [ 58 , 59 ]. Higher concentration of anthocyanin accumulating in a plant results in lower BL interception, which consequently lead to lower biomass production over the long term. Further to this, in this study, we found the ratio of Chl a:b is similar under BL and FL across accessions. This consistency in Chl a:b, suggests a lack of photosystems reconfiguration under BL [ 60 , 61 ]. Our results confirm the role of BL in stimulating anthocyanin content in plants and protecting them from light stress [ 62 ]. Plants activate photo-protective mechanisms under BL to cope with a potential induced-light stress, resulting in an increased accumulation of photo-protective pigments [ 58 , 59 ]. Notably, we found different patterns in content of anthocyanin accumulation in the accessions. Results showed that anthocyanin accumulation can be triggered at low BL (~70 μmol m -2 sec -1 ), which suggests that this protective mechanism against BL can vary based on the accession (i.e. natural adaptations) and can be triggered under low light. Further investigation on these two accessions on BL with a wide range of BL intensity is required. Our results thus encourage future studies analyzing this trait using BL with a wide range of BL intensity to further advance our understanding of the underlying mechanisms.

Plants showed high antioxidative and photo-protective under AL

AL had no impact on the photosynthetic activity across the three accessions compared to FL; yet it induced the poorest morphological traits. Col-0 and C24 showed a severe reduction ‬‬in leaf area growth and biomass, while Est-1 was unaffected. These two accessions (Col-0 and C24) showed a clear elongation of petioles under AL, which suggests that leaf resources are redirected from leaves to petioles as insufficient lighting conditions under AL were performed in this study [ 63 ]. However, the results on transcriptional changes and photosynthates content showed the opposite responses to the morphological traits.

The photosynthates, including proteins and starches, showed lower content in leaves of plants treated under AL. A downregulation of RBCS1A (small subunit of Rubisco) transcription was also observed in the leaves treated under AL. A lower accumulation of proteins was previously observed under AL [ 64 ], suggesting a positive contribution of downregulated Rubisco genes, as it is the main protein in leaves. A lower content of carbohydrates under stress conditions has been observed before in A . thaliana [ 65 ]. Future work is needed to explore if a reduced conversion of light energy into chemical energy has occurred in the photosynthesis process under AL.

High capacity for lipids accumulation was observed for plants treated under AL. Lipid accumulation had been previously linked to oxidative stress [ 66 ]. suggesting an increase in lipophilic antioxidants content such as tocopherols, which play an important role in the scavenging of singlet oxygen [ 67 ]. Moreover, we found a significant increase in both expression and enzymatic activity of antioxidants under AL. Plants stimulate antioxidative mechanisms to protect the photosynthetic apparatus from incurring damage via ROS detoxification [ 30 , 68 ]. Our results on photosynthates thus suggest that plants tried to cope with a potential ROS stress condition under AL.

A significant upregulation in glutathione biosynthesis, transcription level of PGRL1B , ATPC1 , and marker genes associated with ATP synthase and CET complex was observed. In agreement with this result, a significant increase in the expression of ATPC1 at the protein level was recently reported in A . thaliana Col-0 treated with 595 nm light [ 69 ]. CET plays an important role to protect plants under high light and other stress environments [ 70 ]. During CET, electrons are cycled around PSI and protons are translocated to generate a proton gradient across the thylakoid membranes [ 71 ]. In addition to contributing ATP synthesis, another function of a generated proton gradient is to dissipate excess energy as heat from the PSII antennae [ 72 ]. Further to this, an upregulation of CET and ATP synthase suggests of an accelerated rate of PSII repair through elevated ATP synthesis [ 73 , 74 ]. As such, the results on photosynthates and at the transcription level under AL both suggest that AL, even at low light, induces protective mechanisms of photosystems related to light stress, which consequently triggers low protein and starch accumulation and result in poor morphological traits.

One possible hypothesis for the conflicting AL responses can be explained by the detour effect [ 75 , 76 ], where a major part of AL transmitted into the leaf is reflected within leaf tissues and re-absorbed by unsaturated chlorophylls multiple times, which leads to an observed light stress response. Due to the nature of the high absorbing efficiency of the chloroplast, nearly 90% of BL and RL are absorbed at the leaf surface and their detour effect is small [ 76 , 77 ]. While for the wavelength within 500–600 nm [i.e. green light (GL) and AL] that are less absorbed by chloroplast, its light path can increase by several folds and this results in its increased/overexpressed photosynthetic activity through light absorption by unsaturated chloroplast. Although there is no study reporting the underlying mechanisms triggered by AL, several studies have observed the impact of supplemented GL and AL on photosynthetic activity and plant productivity in horticultural plants, which reinforces our hypothesis on the increased photosynthetic activity under AL. Further to this, the aggressive suppression responses on morphological traits in A . thaliana under AL, opposed to the positive impact on plant development, is expected as A . thaliana is a low light plant. They are more sensitive to the change in light properties. Overall, our results suggest AL as a potential light source in activating the potential of increased plant productivity efficiently, but it requires high control on its intensity. This study clarifies why AL alone induces overexpressed high photosynthetic activity yet results in poor plant development.

RL modulated plant adaptation and energy assimilation

The leaf area growth was significantly increased under RL across all accessions, which in turn enabled a greater light interception by the leaves [ 78 ]. This agrees with the increased Pn that was observed across accessions. These observations along with a significant increase of leaf biomass suggests proper plant adaptation under RL across accessions. We found a significant increase in the Chl a: b under RL across accession. Chl a is mainly concentrated around PSI and PSII, whereas Chl b is most abundant in light-harvesting complexes [ 79 ]. An increase in Chl a: b can increase the likelihood of an efficient electron transfer system within the chloroplast membrane [ 80 ]. This, in turn, could positively influence the photosynthetic performance in plants under RL. Considering that timely synthesis of D1 protein is key to maintain the PSII function and consequently, photosynthetic performance in leaves [ 25 ]. An increasing trend of PSBA expression was observed in plants under RL. The PSBA gene is critical for the de novo synthesis of the D1 protein during PSII repairs [ 81 , 82 ]. Therefore, upregulated transcription of PSBA gene could play an important role in accelerating the process of D1 protein turnover under RL. Plants showed that leaf photosynthates (starches, lipids, proteins) increased under RL. Overall, our results present RL as an efficient light source in helping the leaf energy assimilation process, resulting in an increased leaf growth, photosynthetic performance, and photosynthates content in plants.

Supporting information

https://doi.org/10.1371/journal.pone.0247380.s001

S1 Table. List of primers sequences used in qPCR experiments.

https://doi.org/10.1371/journal.pone.0247380.s002

S1 Fig. Proteins involved in ATP synthase and CET complex of A . thaliana Col-0 are upregulated under AL (595 nm) compared to RL (650 nm).

In this experiment, eleven-leaves plants were grown under AL and RL for 5 days (three biological replicates per light condition). A) The expression pattern of protein members involved in Cyclic electron transfer (CET) complex. B) The expression pattern of protein members involved in ATP synthase complex. Expression levels for each protein is normalized to have mean of zero and standard deviation of one. Yellow or blue color indicates upregulation or downregulation, respectively.

https://doi.org/10.1371/journal.pone.0247380.s003

• View Article
• PubMed/NCBI
• Google Scholar
• 31. <oj/>E. W. Schwieterman, "Surface and temporal biosignatures," arXiv preprint arXiv:1803.05065, 2018.
• 38. Hoagland D. R. and Arnon D. I., The water-culture method for growing plants without soil . Berkely,: The College of Agriculture, 1950, p. 32 p.
• 54. Hoover W. H., The dependence of carbon dioxide assimilation in a higher plant on wave length of radiation . City of Washington,: The Smithsonian institution, 1937, p. 1 p.

How do plants grow toward the light? Scientists explain mechanism behind phototropism

Plants have developed a number of strategies to capture the maximum amount of sunlight through their leaves. As we know from looking at plants on a windowsill, they grow toward the sunlight to be able to generate energy by photosynthesis. Now an international team of scientists has provided definitive insights into the driving force behind this movement -- the plant hormone auxin.

The growth of plants toward light is particularly important at the beginning of their lifecycle. Many seeds germinate in the soil and get their nutrition in the dark from their limited reserves of starch and lipids. Reaching for the surface, the seedlings rapidly grow upwards against the gravitational pull, which provides an initial clue for orientation. With the help of highly sensitive light-sensing proteins, they find the shortest route to the sunlight -- and are even able to bend in the direction of the light source.

"Even mature plants bend toward the strongest light. They do this by elongating the cells of the stem on the side that is farthest from the light. This type of light-oriented growth is called phototropism," explains Prof. Claus Schwechheimer from the Chair of Plant Systems Biology at the Technische Universität München (TUM).

Transporters move plant hormone to target site

The substance responsible for cell elongation is auxin. This phytohormone is formed in cells at the tip of the shoot and is then passed from cell to cell. As such, the hormone is shuttled through many cells of the plant before it reaches its final destination. "Export and import proteins push the auxin out of one cell into the intercellular space and then into the next cell and so on until the auxin eventually reaches its target site," outlines Schwechheimer.

The most important proteins in this process are the export proteins known as "PINs," which regulate the direction of the auxin flow. As Schwechheimer's team was able to demonstrate, these PINs do not function on their own: "They require the signal of the D6PK protein kinase," Schwechheimer continues. "The kinase enzyme modifies the PINs through the transfer of phosphate groups -- thus activating them as auxin transporters."

What is the role of auxin?

The movements of plants were first described comprehensively by Charles Darwin in 1880 in his seminal work "The power of movement in plants." The theory that the plant hormone auxin could play a role in plants bending toward a light source was first proposed in 1937 by the Dutch researcher Frits Went in the Cholodny-Went model.

Even though many subsequent observations have supported this model, up to now there has been no definite proof that auxin is in fact involved in this process. Prof. Christian Fankhauser from UNIL (Université de Lausanne) in Switzerland explains why: "Up to now, all plants with a known defect in auxin transport showed a normal phototropism. How then could auxin transport be essential for this process?"

Auxin regulation model confirmed

The TUM team, in cooperation with their colleagues at UNIL, have found the answer to this question. The Swiss researchers were able to inactivate several PIN transporters in a plant simultaneously. And for their part, the TUM scientists managed to demonstrate the function of the D6PK protein kinase.

It was found that when several of the PIN and kinase components were missing, plant growth was completely unresponsive to the light signals that trigger phototropism. The auxin transport mechanism in these mutant plants was severely impaired: The plants grew upwards, away from the gravitational pull, irrespective of the light source. This helped the scientists prove for the first time that the hormone auxin definitely is the substance that drives phototropism.

• Endangered Plants
• Molecular Biology
• Rainforests
• Exotic Species
• Sustainability
• Chloroplast
• Plant sexuality
• Phytoplankton
• Chlorophyll

Story Source:

Materials provided by Technische Universitaet Muenchen . Note: Content may be edited for style and length.

Journal Reference :

• B. C. Willige, S. Ahlers, M. Zourelidou, I. C. R. Barbosa, E. Demarsy, M. Trevisan, P. A. Davis, M. R. G. Roelfsema, R. Hangarter, C. Fankhauser, C. Schwechheimer. D6PK AGCVIII Kinases Are Required for Auxin Transport and Phototropic Hypocotyl Bending in Arabidopsis . The Plant Cell , 2013; DOI: 10.1105/tpc.113.111484

Cite This Page :

Explore More

• Future Climate Impacts Put Whale Diet at Risk
• Charge Your Laptop in a Minute?
• Caterpillars Detect Predators by Electricity
• 'Electronic Spider Silk' Printed On Human Skin
• Engineered Surfaces Made to Shed Heat
• Innovative Material for Sustainable Building
• Human Brain: New Gene Transcripts
• Epstein-Barr Virus and Resulting Diseases
• Origins of the Proton's Spin
• Symbiotic Bacteria Communicate With Plants

Trending Topics

Strange & offbeat.

Light-Quality Manipulation to Control Plant Growth and Photomorphogenesis in Greenhouse Horticulture: The State of the Art and the Opportunities of Modern LED Systems

• Open access
• Published: 23 March 2021
• Volume 41 , pages 742–780, ( 2022 )

Cite this article

You have full access to this open access article

• Roberta Paradiso   ORCID: orcid.org/0000-0002-5577-0008 1 &
• Simona Proietti   ORCID: orcid.org/0000-0003-4136-9800 2  

174 Citations

4 Altmetric

Explore all metrics

Light quantity (intensity and photoperiod) and quality (spectral composition) affect plant growth and physiology and interact with other environmental parameters and cultivation factors in determining the plant behaviour. More than providing the energy for photosynthesis, light also dictates specific signals which regulate plant development, shaping and metabolism, in the complex phenomenon of photomorphogenesis, driven by light colours. These are perceived even at very low intensity by five classes of specific photoreceptors, which have been characterized in their biochemical features and physiological roles. Knowledge about plant photomorphogenesis increased dramatically during the last years, also thanks the diffusion of light-emitting diodes (LEDs), which offer several advantages compared to the conventional light sources, such as the possibility to tailor the light spectrum and to regulate the light intensity, depending on the specific requirements of the different crops and development stages. This knowledge could be profitably applied in greenhouse horticulture to improve production schedules and crop yield and quality. This article presents a brief overview on the effects of light spectrum of artificial lighting on plant growth and photomorphogenesis in vegetable and ornamental crops, and on the state of the art of the research on LEDs in greenhouse horticulture. Particularly, we analysed these effects by approaching, when possible, each single-light waveband, as most of the review works available in the literature considers the influence of combined spectra.

Similar content being viewed by others

LED Lighting in Horticulture

Light quality as a driver of photosynthetic apparatus development

Regulation of gene expression by led lighting.

Avoid common mistakes on your manuscript.

Introduction

Light is one of the main environmental parameters regulating plant physiology throughout the entire plant life cycle, as plants use light as both energy source for carbon fixation in photosynthesis (assimilative function), and signal to activate and regulate many other key processes related to plant growth and development (control function) (Devlin et al. 2007 ).

As their life depends on the assimilative function of light, plants evolved fine light-sensing mechanisms to maintain and maximize photosynthetic performance and fitness during their life span. Through these mechanisms, plants acclimate to a given light environment by means of adjustments of photosynthetic biochemistry (e.g. Rubisco content and change in PSII and PSI ratio), leaf anatomy (e.g. chloroplast size and distribution) and morphology (e.g. leaf surface and thickness), to maximize light harvesting and CO 2 capture (Terashima et al. 2006 ; Athanasiou et al. 2010 ; Kono and Terashima 2014 ; Vialet-Chabrand et al. 2017 ). On the other hand, the control function of light acts as an environmental signalling, perceived by a very sensitive detection system, regulating the plant photomorphogenetic responses, including the transition from a development stage to the next (Devlin et al. 2007 ). For instance, light induces the breaking of seed dormancy and drives the seedling development from a dark- to a light-grown status, inducing the cotyledon expansion and the development of chloroplasts (de-etiolation), enabling the photosynthesis and the achievement of the autotrophy (Folta and Childers 2008 ). During plant growth, light affects stem elongation, branch emission and leaf expansion, determining the plant architecture, and finally it drives the transition to flowering, fruit setting and seeds production (Paik and Huq 2019 ).

Modern agriculture has evolved towards the application of advanced technologies for plant cultivation in controlled environment, in order to guarantee high crop production even in the presence of unfavourable outdoor conditions, or in high density cultivation systems. In particular, in greenhouse horticulture and in growth chambers (e.g. for nursery or vertical farming), light is a key parameter, and a fine control of light quantity (intensity and duration) and quality (wavelength composition) is a challenge to increase the yield and value of products. In many countries (e.g. in Northern Europe), artificial lighting is applied to integrate the natural light when the solar radiation is insufficient, in terms of both intensity or duration, or variable during the day (e.g. winter season). For this purpose, it is mainly used in the view of the assimilative function to increase the photosynthetic performances, hence the annual productivity and the constancy of products yield and quality. On the other hand, in other agricultural areas (e.g. Mediterranean environment), lighting conditions remain largely uncontrolled and the seasonal trend of solar radiation affects the production scheduling, limiting the crops yield and quality.

Plant productivity is not only influenced by light quantity, as intensity (fluence rate) and duration (photoperiod), but it is also affected by light quality (wavelength composition) that influences plant growth and photomorphogenesis, and tissue composition (reviewed in Ouzounis et al. 2015a ). For instance, red light affects the photosynthetic apparatus development, and red and blue light are most efficiently utilized for photosynthesis (Paradiso et al. 2011a ). Blue light influences stomatal opening, plant height and chlorophyll biosynthesis, while far red light stimulates flowering in long-day plants and red/far red ratio regulates stem elongation and branching, leaf expansion, and reproduction (Zheng et al. 2019 ). Finally, green light can drive long-term development and short-term acclimation to light conditions, acting from a chloroplast scale to a whole-plant level. Indeed, green light penetrates deeply in the leaf mesophyll layers and reaches the lower and inner canopy levels, promoting photosynthesis in the deepest chloroplasts and in the less irradiated leaves and providing signals to respond to the environmental irradiance, hence, improving crop productivity and yield (Smith et al. 2017 ).

These evidences show the importance of the different wavelengths of the light spectrum, alone or in combination, in eliciting morphological and physiological responses of plants (Devlin et al. 2007 ; Folta and Childers 2008 ). However, despite the current knowledge on the spectral dependence of many plant processes, artificial lighting in horticulture is still applied mainly with assimilative or photoperiodic function, and only recent experiences pointed out the possibility to exploit the control function of light. Particularly, in the last years innovative lighting sources, based on light-emitting diodes (LEDs), have been tested in plant cultivation, using different wavelength combinations not only to enhance plant photosynthesis and productivity but also to control photomorphogenetic responses, including bioactive compounds synthesis (Bantis et al. 2018 ).

Recently, the creation of blue LEDs allowed the extension of the spectrum range and also the realization of white light LEDs. This revolutionary progress in the lighting sector was endorsed by the Royal Academy of Sciences of Sweden, which in 2014 conferred the Nobel Prize in Physics for the “invention of blue light-emitting diodes”. Consistently with this acknowledgement, the General Assembly of the United Nations declared the 2015 as the “International Year of Light and Light-Based Technologies”, with the aim to promote knowledge on the potential of light science to contribute to a sustainable development and to improve the life quality in the World.

Referring to the control function of light in plants, recent review papers summarized the most relevant knowledge on the modulatory effects of light spectrum in horticultural crops, with reference to only recent advances (Zheng et al. 2019 ), selected leafy vegetables (Thoma et al. 2020 ) or microgreens (Alrifai et al. 2019 ), LED systems (Bantis et al. 2018 ), and utilization in plant factories in urban horticulture (Kozai 2016 ). Besides, comprehensive overview deepened the influence of LED lighting on the biosynthesis of bioactive compounds and crop quality, in both the visible spectrum (Hasan et al. 2017 ) and the UV region (Rai and Agrawal 2017 ).

Our review summarizes data on plant responses to light spectrum of artificial lighting in vegetable and ornamental crops, in terms of growth and photomorphogenesis, and the state of the art of the research on LEDs in greenhouse horticulture. It is worthy to emphasize that, because of the magnitude of data available and the intense research activity in recent times on this topic, many papers even including relevant findings probably eluded our literature inspection. This particularly happened for articles published in the last months, when our efforts were mainly addressed to writing. Just as an example, we point out the latest collection “Crop Physiology under LED Lighting”, published by the journal Frontiers in Plant Science ( https://www.frontiersin.org/research-topics/12923/crop-physiology-under-led-lighting ; Editors Marcelis L., Goto E., Grodzinski B., Torre S., Wargent J., Bugbee B.).

The Solar Radiation and the Plant Functions

The quantity and quality of the incident light affect both the crop yield and the qualitative characteristics of the produces, by sustaining plant growth and influencing the plant reproduction, and by driving the primary and secondary metabolism. The radiation within the 400–700 nm waveband of photosynthetically active radiation (PAR) controls the photochemical reactions, converting light energy in chemical energy, through the synthesis of ATP and NADPH used to assemble carbon atoms in organic molecules in the Calvin cycle, in the reduction of NO 3 − and in the synthesis of amino acids and lipids (Malkin and Niyogi 2000 ). The useful spectrum for photosynthesis in the range of PAR is perceived through photosynthetic pigments, chlorophylls, carotenoids as β-carotene, zeaxanthin, lutein and lycopene, which respond to precise wavelengths included in this range. Indeed, the light harvesting complex in the thylakoids of chloroplasts includes chlorophyll a and chlorophyll b , showing the peaks of maximum absorption at 430, 662 nm, and at 453, 642 nm, respectively (Ouzounis et al. 2015a ). Carotenoids are accessory photosynthetic pigments, harvesting and transferring light energy to chlorophylls, with absorption peaks in the range of 400–500 nm, showing a key role in plant protection to oxidative stress, by the dissipation of excess light energy absorption by photosystems (Bantis et al. 2018 ).

The light quantity, as intensity and photoperiod, is perceived by plants through a complex mechanism including the light signals perception at the leaf level and their transduction to target systems that activates molecular reactions ensuring the fine control of metabolic processes associated to the induced functions (Paik and Huq 2019 ). For instance, minimal variations of photoperiod can trigger a significant advance or delay in specific physiological responses linked to plant development, such as flowering, tuberization and bud development (Mawphlang and Kharshiing 2017 ). Due to the relevance of these essential functions, plants have developed an endogenous system for a precise measurement of photoperiod, represented by circadian rhythms, synchronized with the prevailing environmental conditions (Battle and Jones 2020 ). Plant response to photoperiod is a wide and complex phenomenon; comprehensive assays can be found for example in Johansson and Köster ( 2019 ) and in Creux and Harmer ( 2019 ).

Referring to the light quality, the influence of the light spectrum on plant growth and development has been highlighted since the last century. Just as a few examples, already in 1948 , Borthwich et al. used coloured glass filters to provide plants with light of different colours, highlighting differential responses in plant behaviour in relation with the spectral characteristics of light (Kasperbauer and Kaul 1996 ). In 1972 , McCree demonstrated that, at the same light intensity, the photosynthetic efficiency changes with the wavelength composition and, in the majority of the species, the most useful wavelengths for photosynthesis are in the blue and red regions, according to a trend strictly correlated to the spectrum of absorption of photosynthetic pigments. Oyaert et al. ( 1999 ) tested coloured polyethylene filters with different B:R and R:FR ratios on Chrysanthemum morifolium plants, highlighting the effects of this tool for growth regulation and quality improvement in ornamental crops.

Nowadays, it is known that the different wavebands of light spectrum transmit to plant photoreceptors specific signals inducing the expression of genes related with physiological and metabolic functions (Fukuda 2013 ; Weller and Kendrik 2015 ). The mechanisms underlying the perception and response of plants to spectral composition of the incident light are the subject of topical studies, focused on the role and functions of specific photoreceptors sensitive to different regions of light spectrum (Mawphlang and Kharshiing 2017 ; Paik and Huq 2019 ).

Different classes of photoreceptors perceive the wavelengths corresponding to blue (B, 445–500 nm), green (G, 500–580 nm), red (R, 620–700 nm), and far red (FR, 700–775 nm), while specific photoreceptors perceive ultraviolet (UV) radiation, in particular the UV-A (315–380 nm) and UV-B (280–315 nm) types (Zheng et al. 2019 ). A very important feature of these molecules is represented by the magnitude of light intensity required to trigger a related response, since they are usually activated by a lower intensity than that required for photosynthetic processes (Costa Galvão and Fankhauser 2015 ). From an operational point of view, this implies the possibility to regulate photomorphogenetic processes through artificial lighting, with relatively small investments in terms of operating costs.

Photomorphogenesis and Photoreceptors

Plants have evolved sophisticated mechanisms to detect and respond to light quantity and quality, activating a network of photosensory pathways which are the basis of photomorphogenesis processes. Photomorphogenesis defines plant morphology and development, phototropic orientation to light, photoperiodic responses, and it induces the synthesis of numerous metabolites essential for plant life (Alrifai et al. 2019 ; Thoma et al. 2020 ).

The different spectra received from a natural or artificial source of light strongly influence the plant behaviour, eliciting different metabolic effects. Besides the photosynthetic pigments, the light perception related to photomorphogenesis counts on other specific photoreceptors, independent to photosynthetic metabolism (Weller and Kendrik 2015 ). These are present in different parts of the plant, and the site of light perception can correspond to the part of the plant responding to the light stimulus (e.g. chloroplasts for their own movement), or it can be distant, as light induces a response by long-distance molecular signals (as in floral transition) (Costa Galvão and Fankhauser 2015 ).

Five classes of photoreceptors proteins were characterized to initiate plant responses to light (Fig.  1 ). The first class is represented by the phytochrome family, absorbing R and FR wavelengths; three different photoreceptor proteins, cryptochromes, phototropins and the ZTL/FKF1/LKP2 complex, absorb B and UV-A wavelengths; the UVR8 is sensitive to UV-B wavelengths (Wu et al. 2012 ). These photoreceptors, except for UVR8, are represented by a family of molecules, with each member encoded by a different gene and showing a high degree of similarity with the others.

Spectral wavelength specificity of the main plant photoreceptors and related plant photomorphogenesis responses. Phytochromes (PHYs), cryptochromes (CRYs), phototropins (PHOTs), Zeitlupe family proteins (ZTL/FKF1/LKP2), and UV resistance Locus 8 (UVR8)

Higher plants contain multiple phytochromes (phy A to phy E) (Hughes 2013 ), three cryptochromes (cry1, cry2 and cry3), two phototropins (phot1 and phot2), and one UVR8 photoreceptor. Moreover, a more complex family of B light absorbing proteins, referred as ZTL/FKF1/LKP2, is defined by a combination of the activity of photoreceptors and F-box proteins within the same molecule (Mawphlang and Kharshiing 2017 ).

Phytochromes

Phytochromes (PHYs) have been found and analysed in plants since 1950 (Borthwick et al. 1952 ). PHYs are soluble proteins, binding phytochromobilin as chromophores, absorbing R and FR light, responsible for different plant light responses (Hughes 2013 ). Light converts PHYs in two photoreversible forms in vivo: Pr absorbing R light, with an absorption peak at 650–670 nm, and Pfr absorbing FR, with an absorption peak at 705–740 nm. Pr absorbs R light and is converted to its active form Pfr; on the contrary, Pfr absorbs FR light and is converted to its inactive form Pr.

The active forms of PHYs translocate from the cytoplasm to the nucleus to regulate the expression of different genes linked to the photomorphogenic responses. PHYs can mediate a Very-Low-Fluence Response (VLFR), a Low Fluence Response (LFR), and a High-Irradiance Response (HIR), in relation to the intensity of incident light. The VLFR is activated by extremely low light intensities and very low levels of Pfr, while higher Pfr levels are needed to induce a LFR response. Instead, the extended or continuous irradiation, with a long exposure to a high light intensity (over 1000 µmol m −2 ), can stimulate HIR. In these processes, phyA and phyB play major roles. PhyA is responsible for the VLFR, given its high sensitivity to R light, and can activate a response also at very low radiative flux (0.1–100 nmol m −2 ), and only a small portion of phyA is converted into its active form (Shinomura et al. 1996 ). PhyB principally triggers LFR, responding to low-irradiation conditions (not exceeding 1000 µmol m −2 ), induced by short exposures to R light. HIR-type responses can involve both phyA and phyB in relation to the R or FR portions. In contrast to LFR, HIR and VLFR do not show R:FR photo-reversibility (Casal et al. 1996 ). VLFR is implemented during light-induced seed germination, as well as LFR-type response is characteristic of seed germination and of responses to short light pulses. HIRs include de-etiolation and anthocyanin accumulation in plants. Some authors showed that the response to red wavelengths can be induced also by cryptochromes, indicating a synergy of photoreceptors to control photomorphogenetic processes (Ahmad et al. 1998 ; Màs et al. 2000 ).

The phytochromes photoequilibrium at plant level, calculated as PPE = Pfr/(Pr + Pfr), is strongly related to the R:FR ratio of the incident light (Demotes-Mainard et al. 2016 ). Spectral composition of the incident light changes during the day and coherently the R:FR ratio varies from 1.15 to 0.70 (Craig and Runkle 2016 ; Wang et al. 2020 ). This value, and consequently the Pfr:Pr ratio, decrease also along the plant canopy from the top to the bottom, as a consequence of the different light exposure and wavelengths penetration. Similarly, a decrease of R:FR and Pfr:Pr ratio occurs in plants surrounded by nearby vegetation. These shading conditions induce a complex response defined shade avoidance, including stem and petiole elongation, lower leaf mass, stomata density and chlorophyll content per unit of leaf area, and early flowering (Casal 2013 ). The shade avoidance response increases the plant survival under unfavourable light conditions; however, it can compromise crop yield when modern intensive cropping methods, based on high planting density, are applied (Wang et al. 2020 ).

Finally, the R:FR ratio also affects the plant mineral nutrition. Nitrogen assimilation is inhibited by a low R:FR ratio, which affects the activity of key enzymes of nitrogen metabolism, such as nitrate and nitrite reductase, and glutamine synthetase. In contrast, a reduced R:FR ratio increases the allocation of nutrients to the plant shoot, resulting in a faster development of the aerial part compared to the roots (Demotes-Mainard et al. 2016 ).

Cryptochrome, Phototropins and ZTL/FKF1/LKP2

Cryptochrome family photoreceptors (CRYs) are flavoproteins activated by B and UV-A light absorption, identified in bacteria, fungi, animals and higher plants (Meng et al. 2013 ). In Arabidopsis , CRYs have a key role in seed germination, leaf senescence, stress responses and regulation of transcription; moreover, they can regulate seedlings de-etiolation and growth in shaded environments, and control plant height, flowering time and circadian rhythms (Devlin et al. 2007 ; Pedmale et al. 2016 ).

CRYs, in synergic action with PHYs, have been identified also as receptors of G light, lacking a specific photosensory system for this region of light spectrum. Battle and Jones ( 2020 ) suggested that CRYs and PHYs can absorb portions of the G waveband, even though with a lower sensitivity compared to that for B and R wavelengths. Smith et al. ( 2017 ) proposed the G light perception, particularly the B/G ratio, as an alternative and a fine tuner signalling for plant reaction to shade, resulting as an additional response of shade avoidance than the R/FR perception. The current knowledge suggests that G until 530 nm is included in the CRYs and phototropins B light response, whereas longer wavelengths of G-Y (570 nm) promote the inactivation of B-light-induced CRYs (Battle and Jones 2020 ), justifying the antagonist mechanism of G and B on photoperception by CRYs (Thoma et al. 2020 ).

Green light can be absorbed also by photosynthetic pigments, underlying the importance of this wavelength for CO 2 assimilation and biomass production, and for both long- and short-term plant responses to environmental conditions (Smith et al. 2017 ). The role of CRYs on regulating processes linked to circadian rhythms, phototropic responses, and metabolites accumulation, confers to plants adaptive advantages and affects important traits associated to productivity and quality of crop (Giliberto et al. 2005 ; Mawphlang and Kharshiing 2017 ).

Phototropins (PHOTs) are plasma membrane-associated Serine-Threonine kinases, showing a photoactivation through phosphorylation induced by B light (Briggs and Christie 2002 ; Christie et al. 2015 ). The function and structure of PHOTs were identified in Arabidopsis thaliana , in which two phototropins, phot1 and phot2, were characterized under a molecular point of view. PHOTs can respond to light environment through the control of plant photosynthetic process. Indeed, PHOTs control the movement, density and rearrangement of chloroplasts in plant leaves, to enhance the photosynthetic light harvesting and to minimize the photo-damage under low or high light conditions, respectively. In Arabidopsis mutants, where phototropins are lacking, a significant reduction of photosynthesis was observed (Boccalandro et al. 2012 ), principally induced to the deficient adjustment of chloroplasts that decreases the use of photosynthetically active radiation (PAR) by plants. PHOTs define also the stomatal opening, for the optimization of CO 2 and water exchange (Boccalandro et al. 2012 ). Although phot1 and phot2 show some functional differences to light responses, they have overlapping functions in plants, with the phot1 activation under a larger range of B light intensity and phot2 activation under higher B intensity.

The family of LOV (Light Oxygen or Voltage) photoreceptors was described and defined in Arabidopsis as Zeitlupe/Flavinbinding Kelch Repeat, F-BOX1/LOV Kelch Protein2 (ZTL/FKF1/LKP2), sensitive to B and UV-A wavelengths, (Nelson et al. 2000 ; Somers et al. 2000 ). Analysis of genes encoding for these photoreceptors shows differences between two genetic groups in dicots and monocots (Taylor et al. 2010 ), underlining different functions for these genes. The high level of structural conservation of gene homologs among monocots and dicots observed indicated their functional conservation to regulate similar developmental pathways across different species (Yon et al. 2016 ). In Arabidopsis , KF1 and LKP2 control circadian rhythm (Baudry et al. 2010 ), photoperiodic flowering (Song et al. 2016 ) and, as soybean GmZTL3 (homolog of Arabidopsis ZTL) has been suggested to control the timing of flowering (Xue et al. 2012 ).

UVR8 Photoreceptors

In addition to the above-mentioned specific photoreceptors for UV-A radiation, plants can also intercept UV-B radiation by means of the UV RESISTENCE LOCUS8 (UVR8) receptors (Wu et al. 2012 ). UVR8 proteins are homodimers in the cytoplasm, binding monomer of tryptophan with a chromophore function. In response to UV-B radiation, these photoreceptors are activated by molecular dissociation. UVR8 monomers are accumulated in the nucleus where they perform its regulatory functions (Jenkins 2014 ). The UV-B photoreceptors allow plants to counteract the harmful effects of UV-B inducing changes in gene expression, leading to morphological adaptations and production of different metabolites, mostly with antioxidant functions. In addition, UVR8 photoreceptors mediate essential processes such as stomatal movements, opening and closure (Huché-Thélier et al. 2015 ). Furthermore, UVR8 defines the chlorophyll a content in response to UV-B wavelengths, determining variation of chlorophyll a / b ratio (Jenkins 2009 ).

Despite the knowledge achieved during the last years on molecular mechanisms of photomorphogenesis, different topics remain unclear as the molecular nature and activity of UVR8 photoreceptors, the uncertainty about the presence in plants of a specific G receptor and the mechanism of synergic action of different photoreceptors in eliciting light responses. Since photoreceptors control plant–environment interactions, more information about their biochemical characteristics might suggest the lighting scheduling more efficient to increase plant fitness, yield and quality in agriculture.

Artificial Lighting in Horticulture: Historical and Modern Light Sources

Electric lamps have been used for artificial lighting in plant cultivation for nearly 150 years (Wheeler 2008 ; Morrow 2008 ). As might be imagined, plant lighting closely followed the paths of lighting for civil use, based on three main technologies: (1) incandescent lighting, which was refined by Edison’s invention of the incandescent filament lamp in 1879; (2) open arc lighting, which typically used carbon rods and became popular for street lighting in some cities in the late 1800s and (3) enclosed gaseous discharge lamps, which were initially developed with mercury vapour in the late 1800s (Wheeler 2008 and references therein).

Among the different lamp types, each fits with specific applications, depending on the purpose of lighting. Referring to assimilation lighting, fluorescent lamps, particularly those having enhanced blue and red spectra (i.e. cool fluorescent white lamps), are widely used in growth chambers, together with additional light sources to achieve a sustained photosynthetic photon fluence. High-intensity discharge (HID) lamps, such as metal halide (MH) and high-pressure sodium lamps (HPS), are typically used in greenhouses and plant growth chambers (Nelson and Bugbee 2014 ). MH lamps can be used to totally replace sunlight or partially supplementing it during periods of low solar radiation. The inclusion of metal halides during manufacture optimizes the spectrum of the emitted radiation. Besides, fluorescent lamps, particularly the white ones, are widely used in phytotrons and for in vitro propagation (Darko et al. 2014 ).

HID lamps have high fluence and a good efficiency in energy conversion (light emitted per unit of energy consumed) to PAR (until 50%); however, they show some disadvantages, including the relevant energy requirement, the bulky volume and the high operational temperature, which prevent the placement close to the canopy (even though the heat emission is used in temperature control in Northern countries), and the risk inherent the presence of pressurized gas in glass bulbs. In addition, the spectral distribution shows a high proportion of green-yellow region, significant ultraviolet radiation, scarce blue and FR, altered and instable R:FR ratio, and does not allow modulation of light spectrum. Hence, HIDs are neither spectrally nor energetically optimal. Besides, they are considered not environmental friendly, because of CO 2 emissions and light pollution, particularly in Northern countries, where greenhouse lighting is widely spread (Pinho et al. 2012 ; Battistelli 2013 ).

Fundamental advances in plant artificial lighting started in the mid 1980s when tests with light-emitting diodes (LEDs) begun. LEDs are solid-state semi-conductors and generate light through electroluminescence and, thus, are fundamentally different from other lamps used to date in plants and are the first light source suitable to control light spectral composition and to regulate intensity. Indeed, depending on the semi-conductor used, they produce light at specific wavelengths (colours) of the visible spectrum and beyond, from 250 nm (ultraviolet C) to 1000 nm (infrared), in relatively narrow wavebands, offering the possibility of a targeted compilation of the spectrum. They show higher energy efficiency compared to the traditional light sources (Cocetta et al. 2017 ) and, thanks to the solid state, they are safer and more robust than lamps with filament, pressurized gas, or mercury in glass and are suitable to be used at low temperature (till − 40 °C) and high humidity (Nelson and Bugbee 2014 ). The lower heat radiation does not interfere with controlled climate and, also thanks to the smaller volume, allows to place the lamps close to the canopy, in modern multi-layer and interlighting systems. In addition, they are suitable to be powered by low voltage, with consequent advantages in engineering, and the insensitivity to the switching frequency determines lower cost for maintenance and longer duration. Finally, LEDs equipped with driver chips provide the additional benefits of operational flexibility, suitability for digital control and light protocols (i.e. daily light integral), while the dimmability makes possible the simulation of sunrise and sunset.

LEDs duration is determined differently compared to traditional lamps. Indeed, since this type of light source does not burn out but only tends to attenuation of intensity over time, duration is better expressed as time of operation until 70% of the original intensity. Individual high-brightness LEDs have a predicted lifetime up to 50,000 h (corresponding to about 16.7 years when used an average of 8 h per day), when operated at favourable temperatures, which is 2–3 times higher than fluorescent and HID lamps (for details about technical parameters see Nelson and Bugbee 2014 ).

Despite the numerous advantages, LEDs still present several constraints, such as the higher cost compared the traditional light sources, the difficulty to obtain diffused light and the risks of eye damage for operators in case of prolonged exposure (e.g. for UV emission of blue and white LEDs).

Monochromatic Light and Photomorphogenesis in Vegetable and Flower Crops

Much of the early work on plant production under LEDs was conducted by researchers affiliated with NASA (National Aeronautics and Space Administration of United States) and aimed to design lighting systems for plant cultivation in Space, to develop plant-based regenerative life-support systems for future Moon and Mars colonies (Bula et al. 1991 ). Later on, LED lighting systems have been studied to totally replace traditional light sources in space greenhouses, as reviewed by Zabel et al. ( 2016 ) and Berkovich et al. ( 2017 ), to optimize crop production and quality in Space through specific light recipes to be used in plant chambers aboard of space outposts such as the International Space Station (ISS) (Mickens et al. 2018 ).

LEDs of different colours can be combined to obtain a tailored light spectrum at the desired intensity to modulate the different plant functions, providing a useful tool to control plant growth and photomorphogenesis (Darko et al. 2014 ). Accordingly, they can be used for several purposes, such as the control of size in potted ornamentals, the scheduling of flowering in cut flower crops, the strengthening of mechanisms of stress tolerance and the improvement of chemical composition of plant food (Huché-Thélier et al. 2015 ; Singh et al. 2015 ). In this respect, it is worth noting that, even though a distinction is often done between assimilation light and control light, the latter also influences the biomass accumulation. For instance, blue light, which has an important role in controlling plant height, can improve photosynthetic capacity per leaf area unit by increasing both the stomatal opening and the quantum yield. On the other hand, leaf area itself influences photosynthesis and plant growth, by determining light interception through the leaf surface, morphology and orientation. This is particularly important in noncontinuous canopies (e.g. young plants), where the incident light is only partially intercepted and photomorphogenetic responses have a relevant impact on plant growth and productivity (Hogewoning et al. 2010 ). Accordingly, He et al. ( 2019 ) highlighted that the impact of LED light quality on productivity can be linked to the induced modification of leaf traits more than the change in photosynthetic performance on a leaf area basis. However, it has to be taken into account that also the arrangement of light sources affects the light use efficiency (Paradiso and Marcelis 2012 ; Paradiso et al. 2020 ).

In the early studies, plant response to monochromatic light was investigated mainly in instantaneous measurements and after short exposure, while data collection on long-term acclimation of the whole crops started later and were focused at the beginning on plant adaptability and growth and yield. Yet, the last generation experiments have been concentrating on plant metabolism. Particularly, more than primary metabolism, consisting in essential synthesis mechanisms directly involved in plants growth, development and reproduction, current research frequently deals with the secondary metabolism, responsible for production of minor compounds, such as carotenoids, phenolics (particularly anthocyanins and flavonols), ascorbate and glutathione that, despite the occurrence in low concentrations, contribute to plant adaptability and acclimation to changeable environment and tolerance to biotic and abiotic stresses (Thoma et al. 2020 ). Typical functions of secondary metabolites are cell pigmentation, to attract pollinators and seed dispersers, and antioxidant activity, useful in protection against UV radiation or other stresses. In addition, they are crucial for nutritional quality of plant food for humans as they display various beneficial healthy effects, most related to the antioxidant activity.

Many recent researches focused on the identification of the best combination of light intensity and light quality for vegetable crops, to promote the most suitable composition of plant tissue for human nutrition; however, the plethora of additional environmental (temperature and relative humidity) or cultivation variables (e.g. fertilization) complicate defining specific light recipes.

The following paragraphs summarises the most relevant evidences observed in plant growth and photomorphogenesis as response to changes in light environment by means of LEDs, in both vegetable and flower crops, and information useful to design LED-based lighting systems, depending on the crop and the desired response. Some details of the most relevant cited works are given in Tables 1 , 2 , and 3 , for leaf vegetables, fruit vegetables and flower crops, respectively. Data on the effects of light spectrum treatments on photosynthesis are reported when given; however, they do not fall within the main topics of this review. Unless it is not differently specified, all data refer to plants during cultivation and, for vegetables, chemical composition concerns the edible part of the plant (e.g. leaves and fruits). In a few cases, data on in vitro plantlets or on seedlings are reported for those crops in which LED application focuses on plant propagation.

Red and Blue Light

Vegetable crops.

Early tests of Space research mainly concerned LED R light and demonstrated the need for B radiation to obtain a balanced plant growth. Bula et al. ( 1991 ) reported that plant growth of lettuce under R LEDs (660 nm) combined with B fluorescent lamps (BF, used as source of B before the invention of blue LEDs) was equivalent to those obtained under cool-white fluorescent light (CWF) combined with incandescent lamps (INC, Table 1 ). Red light determined better growth compared to B light in lettuce (Yanagi et al. 1996 ; Table 1 ). However, in this crop, R alone determined hypocotyl etiolation, but this effect was prevented by B addition (10% of total PPFD) (Hoenecke et al. 1992 ; Table 1 ). Accordingly, experiments on wheat confirmed the need for B radiation to prevent etiolation and demonstrated that seedlings grown under R light only did not synthesized chlorophyll, while the addition of B (6% of 500 μmol m –2  s –1 PPFD) reactivated Chl synthesis (Tripathy and Brown 1995 ). Besides, it was demonstrated that B added to R improved plant photosynthetic performance and growth: in pepper lighted with only R, R + BF and R + FR LEDs compared to MH lamps, plants showed a better growth under the wider spectrum of MH, and decreasing growth under R + BF, only R and R + FR, in the absence of B wavelengths (Brown et al. 1995 ; Table 2 ).

Comparing the effects of R LEDs, R + 1% BF, and R + 10% BF to CWF on wheat (24 h photoperiod, 350 μmol m –2  s –1 PPFD), Goins et al. ( 1997 ) demonstrated that plants could complete a seed-to-seed cycle under continuous R light; however, growth and seeds production improved when B light was added. Specifically, 1% BF determined a plant leaf area similar to that under white light, and 10% B gave the same number of sprouts, while improving photosynthetic rate and dry matter accumulation.

Yorio et al. ( 2001 ) reviewed several previous works and summarized that in lettuce, spinach and radish under R LEDs only, dry matter accumulation was lower than under radiation including 10%BF, at the same total light intensity (Table 1 ); however, in NASA studies, the B requirement for some traits (e.g. stem length) was found to be genotype specific in some crops (e.g. potato). Accordingly, studying the effects of 6 levels of B (from 0.1 to 26%) from HPS and MH filtered light at two intensities (200 and 500 μmol m −2  s −1 ) on lettuce, soybean and wheat, Dougher and Bugbee ( 2001 ) highlighted species-dependent responses and a different sensitivity to the absolute intensity and the proportion of B in the total PPFD in several traits (Table 1 ). For instance, stem length was more influenced by B intensity in lettuce and by B proportion in soybean. Later, Hogewoning et al. ( 2010 ) found a dose-dependent response to B radiation in plant leaf area and dry matter accumulation in cucumber (Table 2 ).

Thanks to the invention of blue LEDs, further researches confirmed promoting effects of B light on stomatal conductance (g s ), as previously shown for photosynthesis, highlighting the role of B radiation in stomatal control in spinach (Ohashi-Kaneko et al. 2007 ) and lettuce (Li and Kubota 2009 ) (Table 1 ), as well as in other vegetable and flower crops (same Authors; Tables 2 and 3 ). Later, van Ieperen et al. ( 2012 ) demonstrated that prolonged plants exposure to different LED spectra (R or B and their combinations) influenced gas exchange not only through the stomatal opening but also the stomatal density, underlying the importance of light composition (and particularly of the B amount) also in transpiration control and plant water relation.

In fruit production, Samuolienė et al. ( 2010 ) reported that in strawberry, additional R–B light at 7:1 ratio resulted in bigger fruits with higher sugar content compared to R alone, which also induced stem elongation and inhibited flowering (Yoshida et al. 2012 ; Table 2 ). In radish, soybean and wheat, the comparison of 3 types of white LEDs, warm (WaL), neutral (NL) and cold (CL) light, with 11, 19 and 28% of B, respectively (PPFD 200 and 500 μmol m −2  s −1 , same R:FR), revealed that the lowest B level of WaL LEDs promoted stem elongation and leaf expansion, while the highest in CL LEDs resulted in more compact plants, and stronger differences among the light sources were found under the lower light intensity (Cope and Bugbee 2013 ; Table 2 ). When grown in a greenhouse, tomato fresh and dry weights were positively affected by supplementation of natural light with W or R LEDs. W light also enhanced the fruit growth rate compared to monochromatic R or B addition or no supplemented light (Lu et al. 2012 ; Table 2 ). A study with two tomato cultivars revealed longer harvest period, and higher number of nodes and fruits and total fresh weight when 95% R + 5% B LEDs were used for intracanopy lighting, compared to natural light (Gómez et al. 2013 ; Table 2 ). Similarly, natural light supplemented with LED white light enhanced a number of leaf characteristics in strawberry, including leaf photosynthetic rates, leaf dry mass, area and specific weight; moreover, average fruit weight and number and soluble solids content were also favoured by supplemental light (Hidaka et al. 2013 ; Table 2 ).

Many results demonstrated that light quantity and quality interact in determining plant photomorphogenesis. In cucumber grown in greenhouse with or without light integration with LEDs, at variable R:B ratios and two daily light integrals, growth parameters always improved under LED additional light (Hernández and Kubota 2014 ; Table 2 ). In particular, no differences were found in plant response to the R:B ratios at high light intensity, while increasing values of leaf Chl content and reduction of leaf dry matter accumulation occurred at increasing doses of B at low intensity (Table 2 ), suggesting that light recipe in terms of spectral composition has to be determined considering the intensity applied. In mini-cucumber, combinations of FR, R and B by top and bottom vertical LEDs resulted in more than 10% increase in fruit yield; moreover, plasma light supplemented with vertical B light from the top of the canopy reduced plant growth and fruit yield in the first month, while FR from the top of the canopy increased fruit yield compared to that from the bottom (Guo et al. 2016 ; Table 2 ). In addition to intracanopy lighting, Song et al. ( 2016 ) tested the impact of different light qualities when applied underneath the plant canopy and found that lighting from both directions positively affected the photosynthetic process, especially under WRB and WB (compared to RB and WRFR) (Table 2 ). The authors also reported different mechanisms of photosynthesis improvement, with intracanopy lighting increasing stomatal conductance, CO 2 supply and electron transport activity, while underneath lighting increasing CO 2 assimilation efficiency and excess energy dissipation leading to higher photosynthetic rate.

Cucumber cultivated under LEDs (14% B, 16% G, 53% R, 17% FR) top lighting or intracanopy lighting showed greater light use efficiency, leaf expansion and stem growth, but decreased number of fruits, with higher fruit abortion rate, and lower flower initiation rate and yield compared to HPS-HPS and HPS-LEDs top lighting—intracanopy lighting combinations (Särkkä et al. 2017 ; Table 2 ).

Several studies report inter- and intra-specific differences with respect to the response to the R:B ratio. The absolute B light intensity rather than the percentage of B was reported to control hypocotyl length and stem extension in tomato (Nanya et al. 2012 ). Son and Oh ( 2013 ) found a decrease in growth rate in lettuce cultivars with the increase in B and UV-A light, while Wang et al. ( 2016 ) reported that leaf photosynthetic capacity and photosynthetic rate increased with decreasing R:B ratio, along with promoted shoot dry weight (Table 1 ). In sweet basil and strawberry, the R:B ratio of 0.7 was found to be optimal based on a range of analyses (morphological, physiological and biochemical elements), among 5 LEDs ratios (0.7, 1.2, 1.5, 5.5) and compared to white fluorescent light as a control (Piovene et al. 2015 ; Tables 1 and 2 ), whereas previously Folta and Childers ( 2008 ) had observed the greatest growth rate of strawberry plants under 34% B–66% R, among 4 different B:R ratios (100–0, 66–34, 34–66, 0–100%). In greenhouse production, Kaiser et al. ( 2019 ) supplied tomato with different R:B ratios (0, 6, 12 and 24%) in integration to sunlight, which resulted in an increase in total biomass and fruit number until the optimum of 12% (Table 2 ). Naznin et al. ( 2019 ) investigated the effect of R:B ratio in lettuce, spinach, kale, basil and pepper, and concluded that additional B is essential to promote growth, pigmentation and antioxidant content of these vegetables, although the optimal ratio is species dependent (Tables 1 and 2 ).

It has been hypothesized that B requirement can vary with plant age, in accordance with the hypothesis that it responds to the plant need to balance leaf expansion, to maximise light interception (which is higher in young plants), while preventing excessive stem elongation (Cope and Bugbee 2013 ). This hypothesis agrees with the evidence that leaf optical properties (absorbance, transmittance and reflectance) depend on leaf ontogenesis (age and position in the canopy), that influences anatomical and functional parameters involved in light absorption, such as pigment composition (Paradiso et al. 2011a , b ; Izzo et al. 2019 ).

In terms of nutritional quality, application of B light promoted antocyanin and carotenoid accumulation in lettuce (Stutte et al. 2009 ; Li and Kubota 2009 ) and of ascorbic acid in lettuce and Japanese green mustard (komatsuna), while these effects did not occur in spinach (Ohashi-Kaneko et al. 2007 ; Table 1 ). Irradiation with B increased the concentration of glucosinolates (beneficial active compounds in Brassicaceae) in cauliflower and of chlorogenic acid (antioxidant polyphenol) in basil and tomato, while reducing dangerous metabolites, such as oxalates and nitrates (Ohashi-Kaneko et al. 2007 ; Taulavuori et al. 2013 ) (Tables 1 and 2 ). Also, light intensity influenced the biosynthesis of secondary metabolites, with increasing light intensity resulting in decrease of amounts of nitrate and oxalate, and increase of ascorbate (Proietti et al. 2004 ), as well as an increase in polyphenols production in herbs (Manukyan 2013 ).

Fan et al. ( 2013 ) reported various responses of nonheading Chinese cabbage under the influence of monochromatic and dichromatic LEDs (Table 1 ). Particularly, R light increased plant height but induced negative effects on chlorophyll and carotenoid concentration, Y light reduced dry mass production, as well as soluble sugar and protein concentration, G light decreased chl a / b ratio, while B and RB light decreased plant height but promoted the concentration of soluble proteins, chlorophylls and carotenoids.

Blue and UV wavelengths are known to be effective in promoting bioactive compounds accumulation in plant tissues by upregulating the expression of synthesis pathways genes (Hasan et al. 2017 ). Bian et al. ( 2015 ) highlighted the promoting effects of B, UV-A and UV-B on the synthesis of phenolic compounds in general and anthocyanins in particular, and of B, R and UV-B on carotenoids, in several vegetables. This is in accordance with focused experience demonstrating that improved accumulation of phenolics can be achieved through discontinuous application of UV-B radiation, without affecting the efficiency of photosynthetic apparatus (Mosadegh et al. 2018 ). Blue light, via the cryptochromes and phototropins, was proved to drive the synthesis of chlorophylls and anthocyanins in strawberry (Kadomura-Ishikawa et al. 2013 ) and of total phenolics and flavonoids in lettuce (Zhang et al. 2018 ).

In two basil cultivars grown under LED continuous spectra, Bantis et al. ( 2016 ) reported that the most B and UV (1%) containing light decreased the shoot/root ratio and increased total phenolic content, while low R:FR ratio (highest in R and FR, and high in B, R) had a positive effect on plant height and enhanced the total biomass production compared to FL (Table 1 ).

In nine tomato genotypes, B supplemented to R light had positive effect on plant biomass, attenuated upward or downward leaf curling due to R only and led to increased soluble protein, chlorophyll and carotenoid concentration (Ouzounis et al. 2016 ; Table 2 ).

No significant effect in carotenoid concentration of lettuce was found under B and R LEDs or under HPS lamps supplementing compared to sunlight (Martineau et al. 2012 ). However, Ouzounis et al. ( 2015a , b ) reported higher pigment (chlorophylls and carotenoids) and phenolic (phenolic acids and flavonoids) content in green and red leaf lettuce under natural light supplemented with B LEDs compared to natural light with HPS; further, they recorded increased stomatal conductance and non-photochemical quenching (NPQ) in green lettuce, while quantum yield of PSII decreased in red lettuce under supplemented B light (Table 1 ).

In potato grown in phytotron under controlled environment, Paradiso et al. ( 2019 ) compared two cultivars and two light sources, white fluorescent tubes (WF) and R and B LEDs at 8:1 ratio (RB) (Table 2 ). Tuber yield was higher under RB in both the cultivars. Light quality did not influence the tuber content of starch and total glycoalkaloids, while it affected differently in the cultivars the protein content and the profile of glycoalkaloids (anti-nutritional factors in potato).

Blue component has been recognized at the basis of morphological alteration in several species. In bean, intumescence and oedema in elder leaves were observed at B doses lower than 10% of total radiation, while in pepper oedema on leaves and flower buds in plants grown under R + B LEDs were not reduced by increasing B intensity (Massa et al. 2008 ). On the contrary, tomato plants under similar R–B combinations showed a normal leaf development, indicating that, within the same botanical family, plant sensitivity to spectral-dependent disorders vary among the species (Massa et al. 2008 ). High B proportion combined with small dose of end-of-day (EOD) FR can suppress intumescence injury in tomato (Eguchi et al. 2016 ). In tomato grown in a climatic chamber at PPFD of 200 μmol m −2  s −1 , R:B (2:1 ratio) induced a significant increase of leaf net photosynthesis and a significant decrease of leaf lamina thickness compared to WF light (Arena et al. 2016 ). Trouwborst et al. ( 2010 ) working with cucumber found extremely curled leaves, as well as higher leaf mass per area and dry mass allocation, but lower leaf appearance rate and plant height under LED (20% B:80% R) intracanopy lighting compared with HPS, both applied to supplement the natural light.

The influence of R or B LED light was investigated also as a short-term treatment before harvest, in different vegetables (as example: Wanlai et al. 2013 ; Kwack et al. 2015 ; Samuolienė et al. 2017 ; Kitazaki et al. 2018 ), as well as in aromatic herbs (as example: Amaki et al. 2011 ) and microgreens (reviewed by Alrifai et al. 2019 ). In these latter, recent researches on variation in productivity, nutritive and functional quality (mineral–carotenoid–polyphenolic profiles and antioxidant capacity) in novel microgreens (amaranth, cress, mizuna, purslane) in response to select spectral bandwidths (red, blue, blue-red) highlighted that optimized genetic background combined with effective light management might facilitate the production of superior functional microgreens (Kyriacou et al. 2019 ).

Flower and Ornamental Crops

In ornamental species, plant shape represents a relevant aspect of ornamental quality hence of commercial value, and plant size is one of the most important features. Blue light is known to inhibit stem elongation in many species, however this response is species dependent, as plant morphological responses to B light, as well as to R:FR ratio, are associated with differences in the relative contributions of blue-sensitive photoreceptors (cryptochromes and phototropins) and phytochromes.

Several experiments were carried out in the first years of testing in the in vitro propagation of orchid species (Table 3 ). In Cymbidium lighted with B and R LEDs in growth chamber, B light reduced the leaf growth while increased the chlorophyll content, compared with WF lamps, while the reverse effect was observed under R light (Tanaka et al. 1998 ). In Oncidium , B, R and FR LEDs in growth chamber increased leaf number and expansion, chlorophyll content and fresh and dry weight compared with WF lamps (Chung et al. 2010 ). In the same species, increasing B (10–30%) over R LED light in growth chambers increased the dry weight and protein accumulation compared with WF lamps (Mengxi et al. 2011 ). In Paphiopedilum , B LED light in growth chamber determined more compact plants, and lower leaf length and width compared with CWF light (Lee et al. 2011 ).

In marigold and salvia seedlings, Heo et al. ( 2002 ) investigated the effects of monochromatic B or R LEDs or mixed radiation from a WF light with B, R and FR LEDs compared with WF only (Table 3 ). Dry weight in marigold increased under R, WF + R or WF and decreased under B, whereas in salvia it was greater under WF + B, WF + R and WF + FR. Stem length was three times greater in B than in FLR or FL in marigold and increased in WF + FR while decreased in R in salvia. The number of flowers in marigold was much higher in WF + R and WF control (five times greater than in B or R), while in salvia it varied slightly in the treatments. Light quality also influenced the duration of the blooming period in both the species. No flower buds were formed under monochromic B or R in salvia and WF + FR inhibited flower formation in marigold.

In roses, B (20%) and R (80%) LED lighting in growth chamber increased the dry weight proportion allocated to the leaves, but decreased plant leaf area, plant height and shoot biomass, without affecting flowering compared to HPS lamps (Terfa et al. 2012a , b ; Table 3 ).

In poinsettia, 80%B + 20%R LED light reduced the plant height and the area of leaves and bracts and the leaf chlorophyll content compared to HPS (5% B), even though with no influence on flowering time and postproduction duration, in both growth chamber and greenhouse (Islam et al. 2012 ; Table 3 ). Similarly, in seed annual species crops ( Antirrhinum , Catharanthus , Celosia , Impatiens , Pelargonium , Petunia , Tagetes , Salvia and Viola ) grown under solar light supplemented with HPS light, increasing doses of B from LEDs (from 0 to 30% of 100 μmol m −2  s −1 total PPF) reduced the plant height compared to R in several species, and in most of them R + B determined similar or better global quality than HPS (Randall and Lopez 2014 ; Table 3 ). Increasing proportion of B (from 20 to 100%, with R varying from 80 to 0%) reduced plant height also in rose and chrysanthemum, while it did not affect it in campanula, compared to R and W light; accordingly, different responses among the species were found in plant biomass accumulation (Ouzounis et al. 2014 ; Table 3 ). Beside the morphological effects, higher B radiation increased the stomatal conductance, without affecting the rate of photosynthesis, indicating an excessive stomatal opening compared to the leaf photosynthetic capacity; on the other hand, high B doses promoted flavonoids and phenolic acids biosynthesis, confirming the contribution of B in improving plant response to stress conditions (Ouzounis et al. 2014 ).

The influence of B radiation was also studied in photoperiodic control of flowering in chrysanthemum, by comparing 4 LED treatments, with increasing duration of light period: RB (11 h R + B), RB + B (11 h RB + 4 h B), LRB + B (15 h RB + 4 h B) and RB + LB (11 h RB e 13 h B), in growth chamber (Jeong et al. 2014 ; Table 3 ). Stem length increased through RB, RB + B, LRB + B and RB + LB treatments, and flowering occurred only under short light duration with RB e RB + B, in accordance with the short day (SD) requirement of the species. As a consequence, in chrysanthemum B light can be used to promote stem elongation with no inhibition of flowering even when it is applied in a 15 h photoperiod.

Fukuda et al. ( 2016 ) investigated the influence of light spectrum on growth and flowering and hormones implied in flowering in petunia (a quantitative long-day plant, LD), comparing R, B and white (W) LEDs at low (L) and high (H) intensity (Table 3 ). Conversely to what expected, R light drastically inhibited shoot elongation, with a parallel reduction of giberellin content, while B-promoted stem growth and giberellin synthesis. Compared to W and B (H and L), R-H light anticipated flowering, which was prevented in R-L, where it was restored by night interruption with B but not by GA application. The Authors concluded that in petunia B and R light represent signals for stem lengthening promotion or inhibition respectively, by means of modulation of GA biosynthesis, and while B is a strong signal for flower initiation, the effect of R depends on the light irradiance, suggesting the existence of a photosynthesis-dependent pathway of flowering in this species.

Several studies demonstrated that the response to monochromatic B light strictly depends on plant genotype. Indeed, whereas certain reports founded that monochromatic B induced the greatest biomass accumulation compared to wider spectra in some species (like balloon flower, Platycodon grandiflorum ; Liu et al. 2014 ), some described inhibited photosynthesis and biomass accumulation under R–B or broader spectra in others (like lettuce; Wang et al. 2016 ; Table 1 ).

Also in ornamental species, some experiments studied the effects of light-quality treatments on secondary metabolism, together with the morphological response. In Dieffenbachia and Ficus grown in greenhouse, supplemental B plus R LEDs increased the plant height, but no apparent effect on sugar, chlorophyll and carotenoid content was observed (Heo et al. 2010 ). In chrysanthemum , Jeong et al. ( 2012 ) characterized 9 polyphenols and highlighted a promoting effects of R and G light on polyphenol biosynthesis (Table 3 ). In Kalanchoe , supplemental LED B light decreased leaf fresh weight and increased flavonoid content and antioxidant activity compared with WF lamps (Nascimento et al. 2013 ; Table 3 ).

In some pot foliage plants (e.g. Guzmania lingulata ), in which the leaf colour and variegation are the main quality parameters, additional R and B LED light can be applied for a limited period at the end of the growing cycle to promote the synthesis of anthocyanins and carotenoids, while improving the leaf pigmentation and plant attractiveness, particularly in northern areas where light intensity might be a limiting factor (De Keyser et al. 2019 ).

As in vegetables, in some ornamentals monochromatic light has been reported to cause leaf curling in many works (Oda et al. 2012 ; Hughes 2013 ; De Keyser et al. 2019 ). For instance, in rose the exposure to only R light determines leaf downwards curling, while B light addition restores the normal morphology (Ouzounis et al. 2014 ; Table 3 ). Light spectrum- induced modifications of leaf anatomy, such as those in leaf thickness, have been proved to depend on changes in leaf anatomy, and particularly in palisade parenchyma (Zheng and Van Labeke 2017 ; Table 3 ).

Far Red Light and Red:Far Red Ratio

In greenhouse vegetables, essential components of marketable value are biomass accumulation and product quality, in terms of both aesthetical aspect and nutritional value. In early experiments, pepper lighted with R, R + BF and R + FR LEDs compared to MH lamps, FR addition (corresponding to a decrease of R:FR ratio) resulted in taller plants with greater stem mass than R alone, prefiguring the importance of FR and FR proportion in photomorphogenetic responses (Brown et al. 1995 ) (Table 1 ). Schuerger et al. ( 1997 ) examined structural changes in pepper leaves under R LEDs combined with FR LEDs (FR, 735 nm) or BF lamps (1%B), compared to MH (20%B) (PPFD 330 μmol m −2  s −1 , photoperiod 12 h). Results showed that leaf anatomy depended more by B level than by R:FR ratio, and the increase of B increased the cross section and the number of chloroplasts, with a consequent increase of photosynthetic activity and biomass accumulation.

Positive effects on plant productivity of photomorphogenetic response promoting biomass accumulation were found in lettuce grown in growth chamber under WF with or without LED light addition: the addition of R did not influence the dry matter accumulation compared to WF, conversely a significant increase was observed under FR, which increased the plant leaf area (Li and Kubota 2009 ; Table 1 ).

In tomato and cucumber grown in greenhouse, the comparison among three lighting treatments in addition to natural light, HPS, B:R LEDs and B:R:FR LED at different percentage, showed that B:R determined more compact plants, with no difference in biomass accumulation compared to HPS, while in B:R:FR the reduction in plant size was related to an increase in fruit weight (+ 15% and + 21%, respectively) (Hogewoning et al. 2012 ; Table 2 ). These results depended on the effect of FR on leaf orientation, which improved light interception even without difference in leaf area and photosynthetic rate. In accordance, it has been demonstrated in tomato that the FR amount (also given in brief treatments at the end of day) influenced the stem architecture (i.e. length of internodes and leaf insertion angle) with consequent reduction of leaves self-shading, which has a relevant impact on light penetration and light use efficiency (Sarlikioti et al. 2011 ). Later, other experiments on cucumber highlighted that the addition of LED R light as interlighting to assimilation HPS light and natural light, in order to raise the R:FR ratio, did not increase fruit yield while promoted Chl synthesis, with consequent increase in fruit colour and improvement of visual appearance (Hao et al. 2016 ; Table 2 ).

The above described results highlighted that it can happen that the addition of R light does not influence directly the biomass accumulation, while it is efficient in exerting photomorphogenetic responses when applied in combination with FR doses able to modify the R:FR ratio. R light alone, however, can be efficient in improving the nutritional value of several vegetable products, by promoting the antioxidant production (Olle and Viršile 2013 ), such as phenols in lettuce (till + 6%; Li and Kubota 2009 ). Conversely, the addition of FR to R can reduce the antioxidant synthesis in some species: for instance, in lettuce an increase in plant biomass was associated to a lower anthocyanin content (Li and Kubota 2009 ; Table 1 ). Conversely, in tomato increasing FR LED light, added to natural light supplemented with HPS, positively affected the stem length and fruit yield in the first month of the trial, as well as carotenoid content during the whole experiment (Hao et al. 2016 ).

In ornamental plants, one of the most striking effect of light composition on plant architecture is the shade avoidance syndrome, occurring in high density canopies in low R:FR conditions, implying increased internode and petiole elongation, inhibited axillary bud outgrowth and leaves hyponasty. In pot and garden chrysanthemum, R LED light increased bud outgrowth while B + FR decreased it and reduced plant height, even though the effect was genotype dependent (Dierck et al. 2017 ). Treatment with B + FR in 25 decapitated cuttings determined a strong elongation of the top-most axillary bud and inhibition of underlying buds in pot and cut flower genotypes. This effect also persisted in greenhouse conditions.

Commercial quality in flowering potted plants strictly depends on flowering characteristics in terms of earliness, duration and intensity (number of flower buds) and on foliage density. These features are usually controlled through genotypes selection, irrigation strategies (e.g. moderate drought stress), temperature control (day–night differential temperature) and growth regulators.

Under natural light conditions, the reduction of R:FR ratio, determined by the increase of canopy density during plant growth, causes some undesired responses (excessive stem elongation, inhibition of buds development), which are usually prevented by the reduction of plant density, the application of chemicals and, more recently, the use of FR filtering films in greenhouse. However, in some crops these strategies could be integrated or replaced by using LEDs, while limiting or avoiding chemicals, if plant response to monochromatic light addition would be known.

In a growth chamber lighted with fluorescent tubes, the plant height was not influenced by the addition of R light (FL + R) and it was increased by the addition of B or FR light (FL + B and FL + FR) in Tagetes erecta , while it increased under all the lighting treatments in Salvia splendens , compared to FL, with a parallel reduction in the number of flowers in presence of B and FR only in Tagetes (Heo et al. 2002 ; Table 3 ).

The importance of the phytochrome photoequilibria (PPE) value induced at plant level by R and FR light in the regulation of the flowering process of long-day (LD) plants has been recently investigated, thanks to the diffusion of LEDs. Photoperiodic light quality affects flowering of LD plants, by influencing the PPE at plant level, however the most effective light spectrum to promote flowering is still unknown for most the flower crops. In photoperiodic species, the addition of FR to R to extend the duration of day or to interrupt the night was proved to be useful to control flowering in LD plants. In fact, it is known that incandescent lamps (Inc) determine an intermediate PPE (0.68), resulting sometimes more efficient of light source with higher R:FR ratio (e.g. fluorescent lamps) which create at plant level a higher PPE. In this respect, the use of combined LEDs (R:FR > 0.66, PPE > 0.63) was useful to replace Inc lamps (R:FR = 0.59), widely used in the past with photoperiodic purpose and now forbidden by law in many countries, with significant advance in flowering of petunia, snapdragon and fuchsia, even though with effects on stem elongation variable among the plant species (Craig and Runkle 2012 ; Table 3 ).

Also in chrysanthemum (short day, SD species), in which flowering is inhibited with night break (NB) with R or B light, the reversibility of this effect by successive exposure to FR flashes indicated the involvement of phytochrome and, more specifically, of two different phytochrome-mediated mechanisms, and that the quality of the light provided during the day influences the quality of the light required for an efficient NB (Higuchi et al. 2012 ). In particular, flowering occurred only under SD conditions, with white or R or B light monochromatic light (W-SD, R-SD and B-SD), however in W-SD, NB with R was more efficient in inhibiting flowering compared to B and FR, on the contrary in B-SD the stronger inhibition was by NB-B and FR. Finally, when B-SD was supplemented by monochromatic R light (B + R-SD), NB-B and NB-FR were not efficient.

In two chrysanthemum cultivars grown under short day photoperiod, treated with night break, shoot elongation was enhanced under treatments that emitted FR compared to short day treatment and R containing LED light with no FR (Liao et al. 2014 ).

Meng and Runkle ( 2014 ) compared INC, HPS and CFL lamps with R + FR + W LEDs for night interruption (NI) to extend day length on seven long-day ornamentals, in a commercial greenhouse, and found that in most species LED, INC and HPS lamps were equally effective in controlling flowering. The same authors investigated whether low intensity B (≈ 1.5 μmol m −2  s −1 ), added to R and/or FR light in NI, influences flowering in five SDPs (chrysanthemum, cosmos, two cultivars of dahlia and marigold) and two LDPs ( dianthus and rudbeckia ), grown in greenhouse under SD (Meng and Runkle 2015 ; Table 3 ). Blue light alone was not perceived as a LD by all the SDPs and LDPs tested. For all SDPs, W LEDs inhibited flowering most effectively and B + R was as effective as W for all species except chrysanthemum. B + FR inhibited flowering of marigold and one dahlia cultivar, but not chrysanthemum and the other dahlia, while was less effective than treatments with R light in marigold. B + R + FR and R + FR similarly delayed flowering of all SDPs, except one dahlia. NI treatments containing R promoted flowering of LD rudbeckia. The authors concluded that in these crops a low intensity B during the night does not influence flowering, and that W LEDs that emit little FR light are effective at creating LD for SDPs and in some LDPs. R light alone can inhibit flowering of SDPs, whereas combinations of R and FR promote flowering of some LDPs.

Whole-plant net assimilation was increased in geranium, snapdragon and impatiens with additional FR radiation, while FR promoted flowering of the LD snapdragon (Park and Runkle 2017 ).

In Phalaenopsis , the possibility to replace the reduction of temperature (8 weeks at 19 °C) respect to vegetative phase (22 °C) to promote flower induction by means of light stimuli was evaluated by applying lighting treatments with a high R:FR (estimated PPE 0.85) or a low R:FR (PPE 0.71) (Dueck et al. 2016 ). Results showed that, even though thermal control determined the highest percentage of multiple inflorescences (regardless of light spectrum), similar results were obtained by the exposure for 8 weeks to R and by cooling for 4 weeks followed by high PPE light (regardless of temperature). These results suggested that hormones responsible for flowering in Phalaenopsis are stimulated by a high PPE during the induction period, and temperature and/or light spectrum in the second part of the treatment are more important to obtain multiple inflorescences, probably through the apical dominance suppression. This prefigures the possibility to integrate with LED lighting the inductive thermal treatment, which is energetically more expensive in the summer.

Photoperiodic lighting with R and FR proportion creating an intermediate PPE (0.63–0.80) has been proved to be more effective to promote flowering in some LD species ( Antirrhinum majus , Fuchsia  ×  hybrida , Petunia  ×  hybrida , Rudbeckia hirta ) compared to a R and FR lighting creating an high PPE (above 0.80) (Craig and Runkle 2016 ) (Table 3 ). However, light requirement in terms of intensity and quality vary among the species and are not known for many crops. Recent experiments on photoperiodic lighting in LD plants showed hybrid-specific responses to both day length and light quality, highlighting that genotype sensitivity to light duration and spectrum should be taken into account to optimize lighting protocols in commercial farms. For instance in Ranunculus asiaticus L., Modarelli et al. ( 2020 ) tested three light sources, with different PPEs induced at plant level, compared to natural light. Results showed differences between the hybrids in plant growth and flowering and also in sensitivity to photoperiodic lighting: this improved plant growth and reduced the flowering time in only one hybrid, with a stronger effect under R:FR 3:1 light (estimated PPE 0.84). In both the hybrids, the increase of FR increased the plant leaf area and elongated the flower stems.

Green Light

Green light is a significant portion of solar radiation. It is known that plant leaves appear in green because they reflect the wavelengths producing this colour, hence G has always been considered little useful for plants, in accordance with the limited absorption capacity of leaf pigments. However, as mentioned, many of the early works with LEDs pointed out that plant growth was better under W light or when G was added to B and R, suggesting a contribution of this minor wavelength. Moreover, sometimes plants under only R and B light showed abnormal colouring, which also made difficult the diagnosis of possible disorders, and recent data indicate that it modulates light-induced plant responses. Indeed, G interacts with FR light in determining some phytochrome responses (Tanada 1997 ), in a complex way that has not been fully clarified to date (Folta and Maruhnich 2007 ; Wang and Folta 2013 ). The coaction of G and other wavebands provides a strategy for plants to precisely tune its morphology to adapt to changing light environment: for instance, G light affects plant biomass and reverses UV-B and B- light-mediated stomatal opening (Wang and Folta 2013 ). Nowadays, it is known that G light penetrates deeper into the plant canopy because of its high transmittance and reflectance, and may potentially increase light interception and whole-canopy photosynthesis, being R and FR absorbed primarily by upper leaves. Moreover, it induces shade avoidance responses and regulates secondary metabolism in plants.

Among the earliest experiments, to evaluate the influence of G light, Kim et al. ( 2005 ) cultivated lettuce under R and B LEDs (RB), with or without the addition of G (6 μmol m −2  s −1 ), at equal values of PPFD (136 μmol m −2  s −1 ). Results did not showed differences in plant growth, however the exposure to higher G levels (RGB, 24% G), CWF (51% G) and green fluorescent light (GF, 86% G) compared to RB determined the highest dry matter accumulation in RGB, despite the lower stomatal conductance compared to CWF and the lowest growth under GF. The authors concluded that the addition of G improved the plant growth until 24% of the total light amount (also in other species), while it reduced it over 50%.

The first studies did not provide clear information about how much the influence of G on plant growth depended on a contribution to plant assimilation or on photomorphogenetic responses. Only later, G light was recognized as able to influence plant morphology by means of effects on leaf expansion, stomatal conductance and stem elongation, through a dual mechanism cryptochrome dependent and cryptochrome independent: nowadays, it is known that the mechanism of G perception fine tunes small adjustments in plant growth and development in concert with that induced by R and B light (Folta and Maruhnich 2007 ).

Terashima et al. ( 2009 ) demonstrated that the addition of high-intensity G to white light improved photosynthesis in sunflower and hypothesized that the contribution of G had been underestimated until then because of the too low levels applied in the experiments. The authors reported that, while R and B are mainly absorbed at the adaxial leaf side, G penetrates in the mesophyll and is absorbed in deeper leaf layers. In this respect, considering that G is able to penetrate deeper and in greater amount in the canopy, the transmitted G light assumed a relevant role in photosynthesis in lower and inner leaves, even though less efficient in terms of quantum yield than R and B. In these parts of the canopy, exposed to an altered light microclimate compared to the upper and outer layers (lower light intensity, depleted in R and B and enriched in G and FR), green wavelengths play a key role in plant assimilation. This also occurs in etiolated plants, with scarce chlorophyll content, during the first phases of emergence.

In lettuce, Johkan et al. ( 2012 ) confirmed that G light determined a substantial contribution at high light intensity to assimilation, to primary and secondary metabolism and to photomorphogenesis. Specifically, the authors determined in growth chamber the precise effect of 3 wavelengths peaks (510, 520 and 530 nm) applied at 3 radiation intensities (100, 200 and 300 μmol m −2  s −1 ), compared to white fluorescent light (FL) (Table 1 ). Plants grown under PPF 300 G light, particularly at 510 nm, showed size and morphology similar to those under FL, confirming the efficiency of G on plant growth and morphogenesis when applied at sufficient doses.

Son and Oh ( 2013 ) determined the effect of R, G and B LED ratios on growth, photosynthetic and antioxidant parameters in two lettuce cultivars, with red (‘Sunmang’) or green (‘Grand Rapid TBR’) leaves in growth chamber, comparing six ratios: R:B 9:1, 8:2, 7:3; R:G:B 9:1:0, 8:1:1, 7:1:2, by LEDs (Table 1 ). Red light improved fresh and dry weight of shoots and roots, and leaf area in combination with B. The substitution of B with G in the presence of a fixed proportion of R enhanced the growth of lettuce. Meanwhile, growth under B led to the accumulation of antioxidants in ‘Sunmang’. The supplemental irradiation of G to a combination of R and B can improve lettuce growth.

In lettuce grown hydroponically in growth chamber under white (W) LED light and supplemental B, G, Y, R or FR, plants were compact and vigorous under WR, while they looked sparse and twisted with WY and WFR, and dwarfed with large leaves under WB (Chen et al. 2016 ; Table 1 ). Compared to W control, fresh weight increased with supplemental R and B, while it decreased with supplemental FR. Chlorophyll and carotenoid contents were significantly higher with supplemental R and B. Supplemental B and G resulted in decrease of nitrate content, and G significantly promoted soluble sugar accumulation. Supplemental FR increased S/R ratio and ascorbic acid accumulation but resulted in lower pigment contents.

Green light positively affected leaf area index (LAI) in cucumber, stem length of tomato, petiole length of radish and specific leaf area of pepper compared to cool-white light (Snowden et al. 2016 ). In general, G light alone reduced chlorophyll concentration in cucumber, while B light alone reduced dry mass, LAI, stem and petiole length in tomato, cucumber, pepper and radish. However, plant response to light spectrum depended on light intensity and varied among the species.

Zheng et al. ( 2019 ) showed the effects of B and G during the dark period in tea plants ( Camellia sinensis L.) to understanding the spectral effects on secondary metabolism and light signalling interactions. Results indicated the possibility of a targeted use of B and G to regulate the amount of functional metabolites, such as anthocyanins, catechins and l -ascorbate, to enhance tea quality and taste and to potentially trigger defense mechanisms in tea plants.

Dou et al. ( 2019 ) investigated the effects of substituting partial R and/or B with G light on plant growth in a green and a purple cultivar of basil (Table 1 ). The net photosynthesis (Pn) did not change in green plants whereas it increased in purple plants in presence of G light compared with RB only. The addition of G induced stem elongation in both the cultivars while did not influence leaf characteristics and yield in green plants and decreased leaf thickness and yield in purple plants,. Concentrations of phenolics and flavonoids, and antioxidant capacity decreased under R:B:G = 74:16:10 and R:B:G = 42:13:45 in green leaves and under R:B:G = 44:24:32 and R:B:G = 42:13:45 in purple leaves. Combining yield and nutritional values, a W light with low G proportion (10%) is recommended for basil production in controlled environment.

In snapdragon grown as bedding plant, under natural light supplemented with HPS or 4 BGR LEDs proportions with or without FR, BGR + FR light led to faster flowering by 7 days on average and also increased the leaf area and plant height in snapdragon compared to HPS light (Poel and Runkle 2017 ; Table 3 ). The authors concluded that radiation quality of supplemental light had a relatively little effect on seedling growth and flowering although in some crops, flowering may be earlier when it includes FR radiation.

Owen and Lopez ( 2017 ; Table 3 ) reported that the foliage colour of geranium and purple fountain grass was enhanced under a low greenhouse daily light integral (9 mol m −2  day −1 ), after 14 days of end-of-production supplemental lighting (100 μmol m −2  s −1 ) of 50:50 or 0:100 R:B LED light. Higher B percentage led to greater stomatal conductance, and phenolic acid and flavonoid production in roses, chrysanthemums and campanulas.

Artificial lighting in horticulture has been used for a long time with both assimilation and photoperiodic functions. More recently, the increasing knowledge in plant photomorphogenesis and metabolism paved the way to the application of innovative lighting systems, as well as of other strategies (e.g. photo-selective greenhouse covers), to control plant development and metabolism by means of light spectrum manipulation. In this respect, the considerable advance in LED technology pushed greatly the research on modern systems, based on monochromatic or multispectral light, as only or additional light source and for both assimilative and control functions.

Based on the current knowledge on plant response in the main horticultural crops, LED lighting could improve the product yield and quality, and the sustainability of the greenhouse industry. In particular, many experiments showed as R light alone can promote the synthesis of pigments and active metabolites in different species, improving the product nutritional quality. Responses to R:FR ratio are well defined, in term of processes such as germination, plant shaping, flowering, photosynthesis and biomass accumulation. Red light interacts with B to regulate plant responses and the optimal R:B ratio enhances photosynthetic capacity and improves growth and yield, when the proper light intensity is applied. Blue wavelengths are known to promote the photosynthetic process by inducing stomatal opening and chloroplast relocation and to increase the accumulation of antioxidant compounds and pigments in vegetables and fruits. Finally, G significantly contributes to photosynthesis and biomass accumulation, particularly in inner and lower leaf layers of the canopy, and can influence secondary metabolism. Besides, G wavelengths can tighter control plant growth and morphology by acclimation to light environment, in concert with R- and B-promoted effects, so it is increasingly considered, although much studies are still needed to better unravel their role.

In conclusion, LEDs could revolutionise the facility greenhouse through the realization of smart lighting systems. However, because of the peculiarity of the emitted light (single colour, narrow band), the precise knowledge of plant responses for the different crops, for any single process and developmental stage, is strictly required for their profitable application. In this respect, even though research on LED lighting of plants has been making fast progresses in the last years, several research gaps still need to be solved. For instance, the optimal light spectrum and intensity required by the different species in each phenological stage to optimize yield and product quality are still not known for many crops. Besides, interactions between light intensity and light spectrum and both these light features with other environmental parameters should be better characterized. These progresses are also desirable in the view of the numerous LED possible applications, including the greenhouse cultivation and the nursery production of many vegetables and ornamentals, the realization of plant food enriched in health-promoting bioactive compounds, the vertical farming in urban environment and in the farer scenario of cultivation on higher plants in bioregenerative life-support systems for human exploration of Space.

Data Availability

Data sharing is not applicable to this article as no new data were created or analysed in this study.

Abbreviations

Blue fluorescent

Chlorophyll

Criptochromes

Cool-white fluorescent

Daily light integral

Electron transport rate

Fluorescent lamp

Fresh weight

Gibberellic acid

Green florescent

Stomatal conductance

High-intensity discharge

High-irradiance response

High-pressure sodium

Incandescent

Leaf area index

Light-emitting diodes

Low-fluence response

Light oxygen or voltage

Metal halide

Night interruption

Night break

Neutral light

Net photosynthesis

Non-photochemical quenching

Photosynthetically active radiation

Phototropins

Photosynthetic photon flux density

Phytochrome photoequilibrium

Phytochrome far red

Phytochrome red

Photosystem I

Photosystem II

Total amount of phytochrome

Shoot/root ratio

Specific leaf area

UV resistance Locus 8

Very-low-fluence response

White light

White fluorescent

Zeitlupe/Flavinbinding Kelch Repeat, F-BOX1/LOV Kelch Protein2

Ahmad M, Jarillo J, Smirnova O, Cashmore AR (1998) The CRY1 blue light photoreceptor of Arabidopsis interacts with phytocrhome A in vitro. Mol Cell 1:939–948

CAS   PubMed   Google Scholar  

Alrifai O, Hao X, Marcone MF, Tsao R (2019) Current review of the modulatory effects of LED lights on photosynthesis of secondary metabolites and future perspectives of microgreen vegetables. J Agric Food Chem 67:6075–6090

Amaki W, Yamazaki N, Ichimura M, Watanabe H (2011) Effects of light quality on the growth and essential oil content in Sweet basil. Acta Hortic 907:91–94

Google Scholar  

Arena C, Tsonev T, Doneva D, De Micco V, Michelozzi M, Brunetti C, Loreto F (2016) The effect of light quality on growth, photosynthesis, leaf anatomy and volatile isoprenoids of a monoterpene-emitting herbaceous species ( Solanum lycopersicum L.) and an isoprene-emitting tree ( Platanus orientalis L.). Environ Exp Bot 130:122–132

CAS   Google Scholar  

Athanasiou K, Dyson BC, Webster RE, Johnson GN (2010) Dynamic acclimation of photosynthesis increases plant fitness in changing environments. Plant Physiol 152:366–373

CAS   PubMed   PubMed Central   Google Scholar  

Bantis F, Ouzounis T, Radoglou K (2016) Artificial LED lighting enhances growth characteristics and total phenolic content of Ocimum basilicum , but variably affects transplant success. Sci Hortic 198:277–283

Bantis F, Smirnakou S, Ouzounis T, Koukounaras A, Ntagkas N, Radoglou K (2018) Current status and recent achievements in the field of horticulture with the use of light-emitting diodes (LEDs). Sci Hortic 235:437–451

Battistelli A (2013) Maximizing efficiency in closed ecosystems. Res Mag 20:7

Battle MW, Jones MA (2020) Cryptochromes integrate green light signals into circadian system. Plant Cell Environ 43:16–27

Baudry A, Ito S, Song YH, Strait AA, Kiba T, Lu S, Kay SA (2010) F-box proteins FKF1 and LKP2 act in concert with ZEITLUPE to control Arabidopsis clock progression. Plant Cell 22:606–622

Berkovich YA, Konovalova IO, Smolyanina SO, Erokhin AN, Avercheva OV, Bassarskaya EM, Tarakanov IG (2017) LED crop illumination inside space greenhouses. REACH 6:11–24

Bian ZH, Yang QC, Liu WK (2015) Effects of light quality on the accumulation of phytochemicals in vegetables produced in controlled environments: a review. J Sci Food Agric 95:869–877

Boccalandro HE, Giordano CV, Ploschuk EL, Piccoli PN, Bottini R, Casal JJ (2012) Phototropins but not cryptochromes mediate the blue light-specific promotion of stomatal conductance, while both enhance photosynthesis and transpiration under full sunlight. Plant Physiol 158:1475–1484

Borthwick HA, Hendricks SB, Parker MW (1948) Action spectrum for photoperiodic control of floral initiation of a long-day plant, Wintex barley ( Hordeum vulgare ). Bot Gaz 110:103–118

Borthwick HA, Hendricks SB, Parker MW, Toole EH, Toole VK (1952) A reversible photoreaction controlling seed germination. Proc Natl Acad Sci USA 38:662

Briggs WR, Christie JM (2002) Phototropins 1 and 2: versatile plant blue-light receptors. Trends Plant Sci 7:204–210

Brown CS, Schuerger AC, Sager JC (1995) Growth and photomorphogenesis of pepper plants grown under red light-emitting diodes supplemented with blue or far-red illumination. J Am Soc Hortic Sci 120:808–813

Bula RJ, Morrow RC, Tibbitts TW, Barta DJ, Ignatius RW, Martin TS (1991) Light emitting diodes as a radiation source for plants. HortScience 26:203–205

Casal JJ (2013) Photoreceptor signaling networks in plant responses to shade. Annu Rev Plant Biol 64:403–427

Casal JJ, Clough RC, Vierstra RD (1996) High-irradiance responses induced by far-red light in grass seedlings of the wild type or overexpressing phytochrome A. Planta 200:132–137

Chen X, Xue X, Guo W, Wang L, Qiao X (2016) Growth and nutritional properties of lettuce affected by mixed irradiation of white and supplemental light provided by light-emitting diode. Sci Hortic 200:111–118

Christie JM, Blackwood L, Petersen J, Sullivan S (2015) Plant flavoprotein photoreceptors. Plant Cell Physiol 56:401–413

Chung JP, Huang CY, Dai TE (2010) Spectral effects on embryogenesis and plantlet growth of Oncidium ‘Gower Ramsey.’ Sci Hortic 124:511–516

Cocetta G, Casciani D, Bulgari R, Musante F, Kołton A, Rossi M, Ferrante A (2017) Light use efficiency for vegetables production in protected and indoor environments. Eur Phys J Plus 132:1–15

Cope KR, Bugbee B (2013) Spectral effects of three types of white light-emitting diodes on plant growth and development: absolute versus relative amounts of blue light. HortScience 48:504–509

Costa Galvão V, Fankhauser C (2015) Sensing the light environment in plants: photoreceptors and early signaling steps. Curr Opin Neurobiol 34:46–53

Craig DS, Runkle ES (2016) An intermediate phytocrome photoequilibria from night-interruption lighting optimally promotes flowering of several long-day plants. Environ Exp Bot 121:132–138

Craig DS, Runkle ES (2012) Using LEDs to quantify the effect of the red to far-red ratio of night-interruption lighting on flowering of photoperiodic crops. Acta Hortic 956:179–186

Creux N, Harmer S (2019) Circadian rhythms in plants. Cold Spring Harb Perspect Biol 11:a034611

Darko E, Heydarizadeh P, Schoefs B, Sabzalian MR (2014) Photosynthesis under artificial light: the shift in primary and secondary metabolism. Philos Trans R Soc B 369:20130243

De Keyser E, Dhooghe E, Christiaens A, Van Labeke MC, Van Huylenbroeck J (2019) LED light quality intensifies leaf pigmentation in ornamental pot plants. Sci Hortic 253:270–275

Demotes-Mainard S, Péron T, Corot A, Bertheloot J, Le Gourrierec J, Pelleschi-Travier S, Crespel L, Morel P, Huché-Thélier L, Boumaza R, Vian A, Guérin V, Leduc N, Sakr S (2016) Plant responses to red and far-red lights, applications in horticulture. Environ Exp Bot 121:4–21

Devlin PF, Christie JM, Terry MJ (2007) Many hands make light work. J Exp Bot 58:3071–3077

Dierck R, Dhooghe E, Van Huylenbroeck J, Van Der Straeten D, De Keyser E (2017) Light quality regulates plant architecture in different genotypes of Chrysanthemum morifolium Ramat. Sci Hortic 218:177–186

Dou H, Niu G, Gu M (2019) Photosynthesis, morphology, yield, and phytochemical accumulation in basil plants influenced by substituting green light for partial red and/or blue light. HortScience 54:1769–1776

Dougher TA, Bugbee B (2001) Differences in the response of wheat, soybean and lettuce to reduced blue radiation. Photochem Photobiol 73:199–207

Dueck T, Van Ieperen W, Taulavuori K (2016) Light perception, signalling and plant responses to spectral quality and photoperiod in natural and horticultural environments. Environ Exp Bot 121:1–3

Eguchi T, Hernández R, Kubota C (2016) End-of-day far-red lighting combined with blue-rich light environment to mitigate intumescence injury of two interspecific tomato rootstocks. Acta Hortic 1134:163–170

Fan X, Zang J, Xu Z, Guo S, Jiao X, Liu X, Gao Y (2013) Effects of different light quality on growth, chlorophyll concentration and chlorophyll biosynthesis precursors of non-heading Chinese cabbage ( Brassica campestris L.). Acta Physiol Plant 35:2721–2726

Folta KM, Maruhnich SA (2007) Green light: a signal to slow down or stop. J Exp Bot 58:3099–3111

Folta KM, Childers KS (2008) Light as a growth regulator: controlling plant biology with narrow-bandwidth solid-state lighting systems. HortScience 43:1957–1964

Fukuda N (2013) Advanced light control technologies in protected horticulture: a review of morphological and physiological responses in plant to light quality and its application. J Dev Sustain Agric 8:32–40

Fukuda N, Ajima C, Yukawa T, Olsen JE (2016) Antagonistic action of blue and red light on shoot elongation in petunia depends on gibberellin, but the effects on flowering are not generally linked to gibberellin. Environ Exp Bot 121:102–111

Giliberto L, Perrotta G, Pallara P, Weller JL, Fraser PD, Bramley PM, Fiore A, Tavazza M, Giuliano G (2005) Manipulation of the blue light photoreceptor cryptochrome 2 in tomato affects vegetative development, flowering time, and fruit antioxidant content. Plant Physiol 137:199–208

Goins GD, Yorio NC, Sanwomm BCS (1997) Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting. J Exp Bot 48:1407–1413

Gómez C, Morrow RC, Bourget CM, Massa GD, Mitchell CA (2013) Comparison of intracanopy light-emitting diode towers and overhead high-pressure sodium lamps for supplemental lighting of greenhouse-grown tomatoes. Hort Technol 23:93–98

Guo X, Hao X, Zheng J, Little C, Kholsa S (2016) Response of greenhouse minicucumber to different vertical spectra of LED lighting under overhead high pressure sodium and plasma lighting. Acta Hortic 1170:1003–1010

Hao X, Little C, Zheng JM, Cao R (2016) Far-red LEDs improve fruit production in greenhouse tomato grown under high-pressure sodium lighting. Acta Hortic 1134:95–102

Hasan M, Bashir T, Ghosh R, Lee SK, Bae H (2017) An overview of LEDs’ effects on the production of bioactive compounds and crop quality. Molecules 22:1420

PubMed Central   Google Scholar  

He J, Qin L, Chow WS (2019) Impacts of LED spectral quality on leafy vegetables: productivity closely linked to photosynthetic performance or associated with leaf traits? Int J Agric Biol Eng 12:16–25

Heo JW, Lee C, Chakrabarty D, Paek K (2002) Growth responses of marigold and salvia bedding plants as affected by monochromic or mixture radiation provided by a light-emitting diode (LED). Plant Growth Regul 38:225–230

Heo JW, Lee YB, Kim DE, Chang YS, Chun C (2010) Effects of supplementary LED lighting on growth and biochemical parameters in Dieffenbachia amoena ‘Camella’ and Ficus elastica ‘Melany.’ J Korean Hortic Sci Technol 28:51–58

Hernández R, Kubota C (2014) Growth and morphological response of cucumber seedlings to supplemental red and blue photon flux ratios under varied solar daily light integrals. Sci Hortic 173:92–99

Hidaka K, Dan K, Imamura H, Miyoshi Y, Takayama T, Sameshima K, Kitano M, Okimura M (2013) Effect of supplemental lighting from different light sources on growth and yield of strawberry. Environ Control Biol 51:41–47

Higuchi Y, Sumitomo K, Oda A, Shimizu H, Hisamatsu T (2012) Day light quality affects the night-break response in the short-day plant chrysanthemum , suggesting differential phytochrome-mediated regulation of flowering. J Plant Physiol 169:1789–1796

Hoenecke ME, Bula RJ, Tibbitts TW (1992) Importance of blue photon levels for lettuce seedlings grown under red-light emitting diodes. HortScience 27:427–430

Hogewoning SW, Trouwborst G, Maljaars H, Poorter H, Van Ieperen W, Harbinson J (2010) Blue light dose–responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light. J Exp Bot 61:3107–3117

Hogewoning SW, Trouwborst G, Meinen E, Van Ieperen W (2012) Finding the optimal growth-light spectrum for greenhouse crops. Acta Hortic 956:357–363

Huché-Thélier L, Crespel L, Le Gourrierec J, Morel P, Sakr S, Leduc N (2015) Light signaling and plant responses to blue and UV radiations—perspectives for applications in horticulture. Environ Exp Bot 121:22–38

Hughes J (2013) Phytochromes cytoplasmic signalling. Annu Rev Plant Biol 64:377–402

Islam MA, Kuwar G, Clarke JL, Blystad DR, Gislerød HR, Olsen JE, Torre S (2012) Artificial light from light emitting diodes (LEDs) with a high portion of blue light results in shorter poinsettias compared to high pressure sodium (HPS) lamps. Sci Hortic 147:136–143

Izzo LG, Arena C, De Micco V, Capozzi F, Aronne G (2019) Light quality shapes morpho-functional traits and pigment content of green and red leaf cultivars of Atriplex hortensis . Sci Hortic 246:942–950

Jeong SW, Park S, Jin JS, Seo ON, Kim GS, Kim YH, Bae H, Lee G, Kim ST, Lee WS, Shin SC (2012) Influences of four different light-emitting diode lights on flowering and polyphenol variations in the leaves of chrysanthemum ( Chrysanthemum morifolium ). J Agric Food Chem 60:9793–9800

Jeong SW, Hogewoning SW, Van Ieperen W (2014) Responses of supplemental blue light on flowering and stem extension growth of cut chrysanthemum . Sci Hortic 165:69–74

Johansson M, Köster T (2019) On the move through time—a historical review of plant clock research. Plant Biol 21:13–20

Johkan M, Shoji K, Goto F, Hahida S, Yoshihara T (2012) Effect of green light wavelength and intensity on photomorphogenesis and photosynthesis in Lactuca sativa . Environ Exp Bot 75:128–133

Jenkins GI (2009) Signal transduction in responses to UV-B radiation. Annu Rev Plant Biol 60:407–431

Jenkins GI (2014) Structure and function of the UV-B photoreceptor UVR8. Curr Opin Struct Biol 29:52–57

Kadomura-Ishikawa Y, Miyawaki K, Noji S, Takahashi A (2013) Phototropin 2 is involved in blue light-induced anthocyanin accumulation in Fragaria x ananassa fruits. J Plant Res 126:847–857

Kaiser E, Ouzounis T, Giday H, Schipper R, Heuvelink E, Marcelis LFM (2019) Adding blue to red supplemental light increases biomass and yield of greenhouse-grown tomatoes, but only to an optimum. Front Plant Sci 9:2002

PubMed   PubMed Central   Google Scholar  

Kamal KY, Khodaeiaminjan M, El-Tantawy AA, Moneim DA, Salam AA, Ash-shormillesy SM, Attia A, Ali MA, Herranz R, El-Esawi MA, Nassrallah AA (2020) Evaluation of growth and nutritional value of Brassica microgreens grown under red, blue and green LEDs combinations. Physiol Plant 169:625–638

Kasperbauer M, Kaul K (1996) Light quantity and quality effects on source-sink relationship during plant growth and development. In: Zamski E, Schaffer AA (eds) Photoassimilate distribution in plants and crops. Marcel Dekker, New York, Basel, Hong Kong, pp 421–440

Kim HH, Wheeler RM, Sager JC, Yorio NC, Goins GD (2005) Light-emitting diodes as an illumination source for plants: a review of research at Kennedy Space Center. Habitation 10:71–78

PubMed   Google Scholar  

Kitazaki K, Fukushima A, Nakabayashi R, Okazaki Y, Kobayashi M, Mori T, Shoji K (2018) Metabolic reprogramming in leaf lettuce grown under different light quality and intensity conditions using narrow-band LEDs. Sci Rep 8:1–12

Kono M, Terashima I (2014) Long-term and short-term responses of the photosynthetic electron transport to fluctuating light. J Photochem Photobiol B 137:89–99

Kopsell DA, Sams CE (2013) Increases in shoot tissue pigments, glucosinolates, and mineral elements in sprouting broccoli after exposure to short-duration blue light from light emitting diodes. J Am Soc Hortic Sci 138:31–37

Kozai T (2016) Why LED lighting for urban agriculture? In: Kozai T, Fujiwara K, Runkle E (eds) LED lighting for urban agriculture. Springer, Singapore, pp 3–18

Kwack Y, Kim KK, Hwang H, Chun C (2015) Growth and quality of sprouts of six vegetables cultivated under different light intensity and quality. Hortic Environ Biotechnol 56:437–443

Kyriacou MC, El-Nakhel C, Pannico A, Graziani G, Soteriou GA, Giordano M, Rouphael Y (2019) Genotype-specific modulatory effects of select spectral bandwidths on the nutritive and phytochemical composition of microgreens. Front Plant Sci 10:1501

Lee YI, Fang W, Chen CC (2011) Effect of six different LED light qualities on the seedling growth of Paphiopedilum orchid in vitro. Acta Hortic 907:389–391

Li Q, Kubota C (2009) Effects of supplemental light quality on growth and phytochemicals of baby leaf lettuce. Environ Exp Bot 67:59–64

Liao Y, Suzuki K, Yu W, Zhuang D, Takai Y, Ogasawara R, Fukui H (2014) Night break effect of LED light with different wavelengths on floral bud differentiation of Chrysanthemum morifolium Ramat ‘Jimba’and ‘Iwa no hakusen.’ Environ Control Biol 52:45–50

Lin KH, Huang MY, Huang WD, Hsu MH, Yang ZW, Yang CM (2013) The effects of red, blue, and white light-emitting diodes on the growth, development, and edible quality of hydroponically grown lettuce ( Lactuca sativa L. var. capitata). Sci Hortic 150:86–91

Liu M, Xu Z, Guo S, Tang C, Liu X, Jao X (2014) Evaluation of leaf morphology, structure and biochemical substance of balloon flower ( Platycodon grandiflorum (Jacq) A DC) plantlets in vitro under different light spectra. Sci Hortic 174:112–118

Lu N, Maruo T, Johkan M, Hohjo M, Tsukagoshi S, Ito Y, Ichimura T, Shinohara Y (2012) Effects of supplemental lighting with light-emitting diodes (LEDs) on tomato yield and quality of single-truss tomato plants grown at high planting density. Environ Control Biol 50:63–74

Malkin R, Niyogi K (2000) Photosynthesis. In: Buchanan B, Gruissem W, Jones R (eds) Biochemistry and molecular biology of plants, 2nd edn. American Society of Plant Physiologists, Rockville, Maryland, USA, pp 568–628

Manukyan A (2013) Effects of PAR and UV-B radiation on herbal yield, bioactive compounds and their antioxidant capacity of some medicinal plants under controlled environmental conditions. Photochem Photobiol 89:406–414

Martineau V, Lefsrud M, Naznin MT, Kopsell DA (2012) Comparison of light-emitting diode and high-pressure sodium light treatments for hydroponics growth of Boston lettuce. HortScience 47:477–482

Màs P, Devlin PF, Panda S, Kay SA (2000) Functional interaction of phytochrome b and cryptochrome 2. Nature 408:207–211

Massa GD, Kim HH, Wheeler RM, Mitchell CA (2008) Plant productivity in response to LED lighting. HortScience 43:1951–1956

Mawphlang O, Kharshiing EV (2017) Photoreceptor mediated plant growth responses: implications for photoreceptor engineering toward improved performance in crops. Front Plant Sci 8:1181

Mc Cree KJ (1972) The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agric Meteorol 9:191–216

Meng Q, Runkle ES (2014) Controlling flowering of photoperiodic ornamental crops with light-emitting diode lamps: a coordinated grower trial. HortTechnology 24:702–711

Meng Q, Runkle ES (2015) Low-intensity blue light in night-interruption lighting does not influence flowering of herbaceous ornamentals. Sci Hortic 186:230–238

Meng Y, Li H, Wang Q, Liu B, Lin C (2013) Blue light-dependent interaction between Cryptochrome2 and CIB1 regulates transcription and leaf senescence in soybean. Plant Cell 25:4405–4420

Mengxi L, Zhigang X, Yang Y, Yijie F (2011) Effects of different spectral lights on Oncidium PLBs induction, proliferation, and plant regeneration. Plant Cell Tissue Organ 106:1–10

Mickens MA, Skoog EJ, Reese LE, Barnwell PL, Spencer LE, Massa GD, Wheeler RM (2018) A strategic approach for investigating light recipes for ‘Outredgeous’ red romaine lettuce using white and monochromatic LEDs. Life Sci Space Res 19:53–62

Modarelli GC, Arena C, Pesce G, Dell’Aversana E, Fusco GM, Carillo P, De Pascale S, Paradiso R (2020) The role of light quality of photoperiodic lighting on photosynthesis, flowering and metabolic profiling in Ranunculus asiaticus L. Physiol Plant. https://doi.org/10.1111/ppl.13122

Article   PubMed   Google Scholar  

Morrow RC (2008) LED lighting in horticulture. HortScience 43:1947–1950

Mosadegh H, Trivellini A, Ferrante A, Lucchesini M, Vernieri P, Mensuali Sodi A (2018) Applications of UV-B lighting to enhance phenolic accumulation of sweet basil. Sci Hortic 229:107–116

Nanya K, Ishigami Y, Hikosaka S, Goto E (2012) Effects of blue and red light on stem elongation and flowering of tomato seedlings. Acta Hortic 956:261–266

Nascimento LB, Leal-Costa MV, Coutinho MA, Moreira ND, Lage CL, Barbi ND, Costa SS, Tavares ES (2013) Increased antioxidant activity and changes in phenolic profile of Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) specimens grown under supplemental blue light. Photochem Photobiol 89:391–399

Naznin M, Lefsrud M, Gravel V, Azad M (2019) Blue light added with red LEDs enhance growth characteristics, pigments content, and antioxidant capacity in lettuce, spinach, kale, basil, and sweet pepper in a controlled environment. Plants 8:93

CAS   PubMed Central   Google Scholar  

Nelson JA, Bugbee B (2014) Economic analysis of greenhouse lighting: light emitting diodes vs high intensity discharge fixtures. PLoS One 9:e99010

Nelson DC, Lasswell J, Rogg LE, Cohen MA, Bartel B (2000) FKF1, a clock-controlled gene that regulates the transition to flowering in Arabidopsis . Cell 101:331–340

Oda A, Narumi T, Li T, Kando T, Higuchi Y, Sumitomo K, Fukai S, Hisamatsu T (2012) CsFTL3, a chrysanthemum FLOWERING LOCUS T-like gene is a key regulator of photoperiodic flowering in chrysanthemums. J Exp Bot 63:1461–1477

Ohashi-Kaneko K, Takase N, Kon N, Fujiwara K, Kurata K (2007) Effects of light quality on growth and vegetable quality in leaf lettuce, spinach and komatsuna. Environ Control Biol 45:189–198

Olle M, Viršile A (2013) The effects of light-emitting diode lighting on greenhouse plant growth and quality. Agric Food Sci 22:223–234

Ouzounis T, Frette X, Rosenqvist E, Ottosen CO (2014) Spectral effects of supplementary lighting on the secondary metabolites in roses, chrysanthemums , and campanulas. J Plant Physiol 171:1491–1499

Ouzounis T, Rosenqvist E, Ottosen CO (2015a) Spectral effects of artificial light on plant physiology and secondary metabolism: a review. HortScience 50:1128–1135

Ouzounis T, Razi Parjikolaei B, Fretté X, Rosenqvist E, Ottosen CO (2015b) Predawn and high intensity application of supplemental blue light decreases the quantum yield of PSII and enhances the amount of phenolic acids, flavonoids, and pigments in Lactuca sativa . Front Plant Sci 6:19

Ouzounis T, Heuvelink E, Ji Y, Schouten HJ, Visser RGF, Marcelis LFM (2016) Blue and red LED lighting effects on plant biomass, stomatal conductance, and metabolite content in nine tomato genotypes. Acta Hortic 1134:251–258

Owen WG, Lopez RG (2017) Geranium and purple fountain grass leaf pigmentation is influenced by end-of-production supplemental lighting with red and blue light-emitting diodes. HortScience 52:236–244

Oyaert E, Volckaert E, Debergh PC (1999) Growth of chrysanthemum under coloured plastic films with different light qualities and quantities. Sci Hortic 79:195–205

Paik I, Huq E (2019) Plant photoreceptors: multi-functional sensory proteins and their signaling networks. Semin Cell Dev Biol 92:114–121

Paradiso R, Marcelis LFM (2012) The effect of irradiating adaxial or abaxial side on photosynthesis of rose leaves. Acta Hortic 956:157–163

Paradiso R, Meinen E, Snel JF, De Visser P, Van Ieperen W, Hogewoning SW, Marcelis LFM (2011a) Spectral dependence of photosynthesis and light absorptance in single leaves and canopy in rose. Sci Hortic 127:548–554

Paradiso R, Meinen E, Snel J, Van Ieperen W, Hogewoning SW, Marcelis LFM (2011b) Light use efficiency at different wavelengths in rose plants. Acta Hortic 893:849–855

Paradiso R, Arena C, Rouphael Y, d’Aquino L, Makris K, Vitaglione P, De Pascale S (2019) Growth, photosynthetic activity and tuber quality of two potato cultivars in controlled environment as affected by light source. Plant Biosyst 153:725–735

Paradiso R, de Visser PHB, Arena C, Marcelis LFM (2020) Light response of photosynthesis and stomatal conductance of rose leaves in the canopy profile: the effect of lighting on the adaxial and the abaxial sides. Funct Plant Biol 47:639–650

Park Y, Runkle ES (2017) Far-red radiation promotes growth of seedlings by increasing leaf expansion and whole-plant net assimilation. Environ Exp Bot 136:41–49

Pedmale UV, Huang SS, Zander M, Cole BJ, Hetzel J, Ljung K, Reis PA, Sridevi P, Nito K, Nery JR, Ecker JR (2016) Cryptochromes interact directly with PIFs to control plant growth in limiting blue light. Cell 164:233–245

Pinho P, Jokinen K, Halonen L (2012) Horticultural lighting—present and future challenges. Light Res Technol 44:427–437

Piovene C, Orsini F, Bosi S, Sanoubar R, Bregola V, Dinelli G, Gianquinto G (2015) Optimal red:blue ratio in led lighting for nutraceutical indoor horticulture. Sci Hortic 193:202–208

Poel BR, Runkle ES (2017) Spectral effects of supplemental greenhouse radiation on growth and flowering of annual bedding plants and vegetable transplants. HortScience 52:1221–1228

Proietti S, Moscatello S, Leccese A, Colla G, Battistelli A (2004) The effect of growing spinach ( Spinacia oleracea L.) at two light intensity on the amounts of oxalate, ascorbate and nitrate in their leaves. J Hortic Sci Biotechnol 79:606–609

Rai K, Agrawal SB (2017) Effects of UV-B radiation on morphological, physiological and biochemical aspects of plants: an overview. J Sci Res 61:87–113

Randall WC, Lopez RG (2014) Comparison of supplemental lighting from high-pressure sodium lamps and light-emitting diodes during bedding plant seedling production. HortScience 49:589–595

Samuolienė G, Brazaitytė A, Urbonavičiūtė A, Šabajevienė G, Duchovskis P (2010) The effect of red and blue light component on the growth and development of frigo strawberries. Zemdirbyste 97:99–104

Samuolienė G, Brazaitytė A, Vaštakaitė V (2017) Light-emitting diodes (LEDs) for improved nutritional quality. In: Dutta Gupta S (ed) Light emitting diodes for agriculture. Springer, Singapore, pp 149–190

Särkkä LE, Jokinen K, Ottosen CO, Kaukoranta T (2017) Effects of HPS and LED lighting on cucumber leaf photosynthesis, light quality penetration and temperature in the canopy, plant morphology and yield. Agric Food Sci 26:102–110

Sarlikioti V, de Visser PH, Buck-Sorlin GH, Marcelis LF (2011) Exploring the spatial distribution of light interception and photosynthesis of canopies by means of a functional–structural plant model. Ann Bot 107:875–883

Schuerger AC, Brown CS, Stryjewski EC (1997) Anatomical features of pepper plants ( Capsicum annuum L.) grown under red light-emitting diodes supplemented with blue or far-red light. Ann Bot 79:273–282

Shinomura T, Nagatani A, Hanzawa M, Kubota M, Watanabe M, Furuya M (1996) Action spectra for phytochrome A- and B-specific photoinduction of seed germination in Arabidopsis thaliana . Proc Natl Acad Sci USA 93(15):8129–8133

Singh D, Basu C, Meinhardt-Wollweber M, Roth B (2015) LEDs for energy efficient greenhouse lighting. Renew Sustain Energy Rev 49:139–147

Smith HL, McAusland L, Murchie EH (2017) Don’t ignore the green light: exploring diverse roles in plant processes. J Exp Bot 68:2099–2110

Snowden MC, Cope KR, Bugbee B (2016) Sensitivity of seven diverse species to blue and green light: interactions with photon flux. PLoS One 11:e0163121

Somers DE, Schultz TF, Milnamow M, Kay SA (2000) ZEITLUPE encodes a novel clock-associated PAS protein from Arabidopsis . Cell 10:319–329

Son KH, Oh MM (2013) Leaf shape, growth, and antioxidant phenolic compounds of two lettuce cultivars grown under various combinations of blue and red light-emitting diodes. HortScience 48:988–995

Song G, Jia M, Chen K, Kong X, Khattak B, Xie C, Mao L (2016) CRISPR/Cas9: a powerful tool for crop genome editing. Crop J 4:75–82

Stutte GW, Edney S, Skerritt T (2009) Photoregulation of bioprotectant content of red leaf lettuce with light-emitting diodes. HortScience 44:79–82

Tanada T (1997) The photoreceptors in the high irradiance response of plants. Physiol Plant 101:451–454

Tanaka M, Takamura T, Watanabe H, Endo M, Yanagi T, Okamoto K (1998) In vitro growth of Cymbidium plantlets cultured under superbright red and blue light-emitting diodes (LEDs). J Hortic Sci Biotechnol 73:39–44

Taulavuori K, Julkunen-Tiitto R, Hyoky V, Taulavuori E (2013) Blue mood for superfood. Nat Prod Commun 8:791–794

Taylor A, Massiah AJ, Thomas B (2010) Conservation of Arabidopsis thaliana photoperiodic flowering time genes in onion ( Allium cepa L.). Plant Cell Physiol 51:1638–1647

Terashima I, Hanba YT, Tazoe Y, Vyas P, Yano S (2006) Irradiance and phenotype: comparative eco-development of sun and shade leaves in relation to photosynthetic CO 2 diffusion. J Exp Bot 57:343–354

Terashima I, Fujita T, Inoue T, Chow WS, Oguchi R (2009) Green light drives leaf photosynthesis more efficiently than red light in strong white light: revisiting the enigmatic question of why leaves are green. Plant Cell Phys 50:684–697

Terfa MT, Poudel MS, Roro AG, Gislerød HR, Olsen JE, Torre S (2012a) Light emitting diodes with a high proportion of blue light affects external and internal quality parameters of pot roses differently than the traditional high pressure sodium lamp. Acta Hortic 956:635–642

Terfa MT, Solhaug KA, Gislerød HR, Olsen JE, Torre S (2012b) A high proportion of blue light increases the photosynthesis capacity and leaf formation rate of Rosa x hybrida but does not affect time to flower opening. Physiol Plant 148:146–159

Thoma F, Somborn-Schulz A, Schlehuber D, Keuter V, Deerberg G (2020) Effects of light on secondary metabolites in selected leafy greens: a review. Front Plant Sci 11:497

Tripathy BC, Brown CS (1995) Root-shoot interaction in the greening of wheat seedlings grown under red light. Plant Physiol 107:407–411

Trouwborst G, Oosterkamp J, Hogewoning SW, Harbinson J, Van Ieperen W (2010) The responses of light interception, photosynthesis and fruit yield of cucumber to LED-lighting within the canopy. Physiol Plant 138:289–300

Van Ieperen W, Savvides A, Fanourakis D (2012) Red and blue light effects during growth on hydraulic and stomatal conductance in leaves of young cucumber plants. Acta Hortic 956:223–230

Vialet-Chabrand S, Matthews JS, Simkin AJ, Raines CA, Lawson T (2017) Importance of fluctuations in light on plant photosynthetic acclimation. Plant Physiol 173:2163–2179

Wang Y, Folta KM (2013) Contributions of green light to plant growth and development. Am J Bot 100:70–78

Wang J, Lu W, Tong Y, Yang Q (2016) Leaf morphology, photosynthetic performance, chlorophyll fluorescence, stomatal development of lettuce ( Lactuca sativa L.) exposed to different ratios of red light to blue light. Front Plant Sci 7:250

Wang X, Gao X, Liu Y, Fan S, Ma Q (2020) Progress of research on the regulatory pathway of the plant shade-avoidance syndrome. Front Plant Sci 11:439

Wanlai Z, Wenke L, Qichang Y (2013) Reducing nitrate content in lettuce by pre-harvest continuous light delivered by red and blue light-emitting diodes. J Plant Nutr 36:481–490

Weller JL, Kendrick RE (2008) Photomorphogenesis and photoperiodism in plants. In: Björn LO (ed) Photobiology: the science of light and life. Springer, New York, pp 299–321

Wheeler RM (2008) A historical background of plant lighting: an introduction to the workshop. Hortic Sci 43:1942–1943

Wu D, Hu Q, Yan Z, Chen W, Yan C, Huang X, Zhang J, Yang P, Deng H, Wang J, Deng X, Shii Y (2012) Structural basis of ultraviolet-B perception by UVR8. Nature 484:214–219

Xue ZG, Zhang XM, Lei CF, Chen XJ, Fu YF (2012) Molecular cloning and functional analysis of one ZEITLUPE homolog GmZTL3 in soybean. Mol Biol Rep 39:1411–1418

Yanagi T, Okamoto K, Takita S (1996) Effect of blue, red, and blue/red lights of two different PPF levels on growth and morphogenesis of lettuce plants. Acta Hortic 440:117–122

Yon F, Joo Y, Cortés Llorca L, Rothe E, Baldwin IT, Kim SG (2016) Silencing Nicotiana attenuata LHY and ZTL alters circadian rhythms in flowers. New Phytol 209:1058–1066

Yoneda Y, Nakashima H, Miyasaka J, Ohdoi K, Shimizu H (2017) Impact of blue, red, and far-red light treatments on gene expression and steviol glycoside accumulation in Stevia rebaudiana . Phytochemistry 137:57–65

Yorio NC, Goins GD, Kagie HR, Wheeler RM, Sager JC (2001) Improving spinach, radish, and lettuce growth under red light-emitting diodes (LEDs) with blue light supplementation. HortScience 36:380–383

Yoshida H, Hikosaka S, Goto E, Takasuna H, Kudou T (2012) Effects of light quality and light period on flowering of everbearing strawberry in a closed plant production system. Acta Hortic 956:107–112

Zabel P, Bamsey M, Schubert D, Tajmar M (2016) Review and analysis of over 40 years of space plant growth systems. Life Sci Space Res 10:1–16

Zhang T, Shi Y, Piao F, Sun Z (2018) Effects of different LED sources on the growth and nitrogen metabolism of lettuce. Plant Cell Tissue Organ Cult (PCTOC) 134:231–240

Zheng L, Van Labeke MC (2017) Long-term effects of red- and blue-light emitting diodes on leaf anatomy and photosynthetic efficiency of three ornamental pot plants. Front Plant Sci 8:1–12

Zheng L, He H, Song W (2019) Application of light-emitting diodes and the effect of light quality on horticultural crops: a review. HortScience 54:1656–1661

Zhiyu M, Shimizu H, Moriizumi S, Miyata M, Douzono M, Tazawa S (2007) Effect of light intensity, quality and photoperiod on stem elongation of chrysanthemum cv. Reagan. Environ Control Biol 45:19–25

Download references

Open access funding provided by Università degli Studi di Napoli Federico II within the CRUI-CARE Agreement.

Author information

Authors and affiliations.

Department of Agricultural Sciences, University of Naples Federico II, Via Università 100, Portici, 80055, Naples, Italy

Roberta Paradiso

Research Institute on Terrestrial Ecosystems (IRET), National Research Council of Italy (CNR), Viale Marconi 2, 05010, Porano, Terni, Italy

Simona Proietti

You can also search for this author in PubMed   Google Scholar

Contributions

The authors contributed to the literature review, the writing of the article and the preparation of the figure and the tables in equal measure.

Corresponding author

Correspondence to Roberta Paradiso .

Ethics declarations

Conflict of interest.

The authors declare that they have no conflict of interest.

Additional information

Handling Editor: Rhonda Peavy.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ .

Reprints and permissions

About this article

Paradiso, R., Proietti, S. Light-Quality Manipulation to Control Plant Growth and Photomorphogenesis in Greenhouse Horticulture: The State of the Art and the Opportunities of Modern LED Systems. J Plant Growth Regul 41 , 742–780 (2022). https://doi.org/10.1007/s00344-021-10337-y

Download citation

Received : 14 October 2020

Accepted : 01 February 2021

Published : 23 March 2021

Issue Date : February 2022

DOI : https://doi.org/10.1007/s00344-021-10337-y

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Light spectrum
• Photoreceptors
• Ornamentals
• Find a journal
• Publish with us
• Track your research

• Free Resources
• Project Search
• Featured Projects
• Member Benefits

1059 Main Avenue, Clifton, NJ 07011

The most valuable resources for teachers and students

(973) 777 - 3113

[email protected]

1059 Main Avenue

Clifton, NJ 07011

07:30 - 19:00

Monday to Friday

123 456 789

[email protected]

Goldsmith Hall

New York, NY 90210

• Why We’re Unique

Plant Growth; How does the hours of sunlight effect plant growth?

Introduction: (initial observation).

In summer time, days are long and we have more hours of sunlight. In winter however the days are short and we only get a few hors of sunlight each day. Do you think that this has any affect on plants life? Is it what causes autumn and falling leaves and finally leafless and almost lifeless trees. Of course cold weather and other factors may also be involved, but it is good if we be able to see how does the hours of sunlight affect a plant growth.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start ” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about the affect of sunlight on plant growth. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

Plants must have light to manufacture food and grow. Light retards stem growth, but promotes leaf expansion . The sunshine helps the plants make their own food. And the leaves take the air into the plants. Air, water, sunshine, and soil help the plants grow. If plants do not get sunlight, they cannot produce chlorophyll and they will lose their green color and eventually die. If plants lack any of the other things they need to grow and make their own energy and food, they will die.

Green plants need these things in order to grow and make their own energy and food:

• Light energy
• Carbon Dioxide
• Chlorophyll

Chlorophyll is the chemical that makes plants green.

Question/ Purpose:

The purpose of this project is to see the effect of sun light on plants and to find out how does the hours of sunlight affect the plant growth?

Identify Variables:

We change the hours of sunlight (hours that plant is exposed to sunlight) to see how does it affect the plant growth. So the hours of sunlight is our independent variable and plant growth is our dependent variable.

Hypothesis:

My hypothesis is that a few hours (about 4 hours) of sunlight is enough for the plant growth. I think excess hours of exposure to sunlight is not beneficial. However very low hours of sunlight can hurt some plants and stop it’s growth. This probably depends on the specific plants.

Experiment Design:

In the first experiment we want to see how effective is sunlight for the general health of a plant. To do that we get a sample plant and somehow we place a part of this plant such as a leaf or a few leaves in the dark. That can be a dark box or dark paper. This is the details:

Experiment 1:

• Take the black construction paper and cut out 4 square or oval pieces. Cover up 2 leaves on the healthy green plant with the black construction paper pieces, one on top of the leaf and one piece on the bottom of the leaf. Secure the papers on the leaf with paper clips.
• Look at your leaves to make sure that the entire leaf area on top and on the bottom is covered up and won’t be able to get any sunlight.
• After a week, remove the paper clips and pieces of black construction paper. What do the leaves look like? What color are they? What do you think happened?
• Leave the plants on the windowsill or table top for another week. Water the plants when needed. Watch the leaves and see what happens to them when they are able to get sunlight again.

Now that we know plants need sunlight, let’s try another experiment to see the effect of hours of sunlight on plant growth.

Experiment 2:

From a bag of lima beans, select 20 large, almost identical beans, Take 4 plates and place 5 beans in each plate. Number the plates from 1 to 4. Pure some water in each place and cover them with cloth. Add water as needed daily to keep the cloth moist, but don’t submerge the beans entirely in water. After a few days, you should see a little sprout coming out of each beans. Remove the cloths from plates as germination continues for a few days till the first leaf appears. Now you need to control the amount of sunlight each plate gets. Take 4 brown paper bags and place them upside down on each plate. Allow plate number one to have 2 hours of sunlight, then cover it with the bag for the rest of the day. Allow plate number two to get 4 hours, plate number three with 6 hours and plate number four with 8 hours of sun light every day. Continue exposing the plates to different hours of sunlight for two weeks and at the end, remove the paper bags and observe all the beans in all plates.

How do they differ from each other ? What plate has the best or tallest or greenest beans leaves ? What do you think happened.

Record he result in the following table by placing an X in appropriate boxes.

Also measure the height of plants once a week and record the results in a table like this. You can use this table to draw a graph or chart.

Notes:  If you live in a warm area or it is the summer time, you can do this experiment outside. But if it is cold out, do your experiment in a warm green house or next to a well lit window that gets lots of sunlight.

Materials and Equipment:

Experiment A

• A green plant with healthy green leaves
• Paper clips
• Black construction paper

Experiment B

• Brown paper bags

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Experiment A results: When you cover the leaves with black construction paper, leaves do not receive sunlight therefore, they can not make Chlorophyll, the green color. As a result, the green color fades away and leave may fall off. Once you place the plant close to window where it can get some sunlight, with little bit of water every day, it begins making the green color and looks healthy again.

Experiment B results: Plates with most sunlight has the best lima leaves.

Calculations:

Does the result of your experiment support your hypothesis? Write your conclusion.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Plants are the only things on earth that turn sunlight into food. They do it through a process called photosynthesis. Photosynthesis means to “put together using light”. Plants use sunlight to turn carbon dioxide from the air, and water into food. Plants need all of these to remain healthy. When the plant gets enough of these things, it produces a simple sugar, which it uses immediately or stores in a converted form of starch. We don’t know exactly how this happens. But we do know that chlorophyll, the green substance in plants, helps it to occur. Without chlorophyll plants can’t make food and without sunlight, there can’t be chlorophyll to make food.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Why plants needs chlorophyll and what is photosynthesis?

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

Experiment A: If the leaves are not fully covered or the clip is not tight, the leaves may get some light and make a little bit of color. The stress, pressure or weight of leaf covering may also have some affects. We must try to minimize any pressure to the plant.

Experiment A: All plates need to be kept close to each other and be at the same temperature. Air movement should be allowed from bottom of bags and water quantity should be identical for all plates.

References:

List of References

www.eecs.umich.edu

www.cals.ncsu.edu

http://scholar.coe.uwf.edu/wbi2000/students/practica/jmesser/plants.htm

http://www.ed.gov/pubs/parents/Science/plants.html

http://www.alienexplorer.com/ecology/e35.html

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

Testimonials

" I called School Time and my husband and son came with me for the tour. We felt the magic immediately."

- Robby Robinson

" My husband and son came with me for the tour. We felt the magic immediately."

- Zoe Ranson

Contact Info

Our address, working hours.

Week Days: 07:00-19:00

Saturday: 09:00-15:00

Sunday: Closed

Science Project

Make a hypothesis about which color in the visible spectrum causes the most plant growth and which color in the visible spectrum causes the least plant growth.

How did you test your hypothesis? Which variables did you control in your experiment and which variable did you change in order to compare your growth results?

Analyze the results of your experiment. Did your data support your hypothesis? Explain. If you conducted tests with more than one type of seed, explain any differences or similarities you found among the types of seeds.

What conclusions can you draw about which color in the visible spectrum causes the most plant growth?

Given that white light contains all colors of the spectrum, what growth results would you expect under white light?

• Carry out an experiment to determine which colors of the light spectrum are used in photosynthesis as evidenced by plant growth.
• Measure plant growth under lights of different colors of the spectrum.

OSU Extension Service

• Gardening, lawn and landscape
• Gardening techniques

Environmental factors affecting plant growth

Plant growth and geographic distribution (where the plant can grow) are greatly affected by the environment. If any environmental factor is less than ideal, it limits a plant's growth and/or distribution. For example, only plants adapted to limited amounts of water can live in deserts.

Either directly or indirectly, most plant problems are caused by environmental stress.

Either directly or indirectly, most plant problems are caused by environmental stress. In some cases, poor environmental conditions (e.g., too little water) damage a plant directly. In other cases, environmental stress weakens a plant and makes it more susceptible to disease or insect attack.

Environmental factors that affect plant growth include light, temperature, water, humidity and nutrition. It's important to understand how these factors affect plant growth and development. With a basic understanding of these factors, you may be able to manipulate plants to meet your needs, whether for increased leaf, flower or fruit production. By recognizing the roles of these factors, you'll also be better able to diagnose plant problems caused by environmental stress.

Three principal characteristics of light affect plant growth: quantity , quality and duration .

Light quantity refers to the intensity, or concentration, of sunlight. It varies with the seasons. The maximum amount of light is present in summer, and the minimum in winter. Up to a point, the more sunlight a plant receives, the greater its capacity for producing food via photosynthesis.

You can manipulate light quantity to achieve different plant growth patterns.

You can manipulate light quantity to achieve different plant growth patterns. Increase light by surrounding plants with reflective materials, a white background or supplemental lights. Decrease it by shading plants with cheesecloth or woven shade cloths.

Light quality refers to the color (wavelength) of light. Sunlight supplies the complete range of wavelengths and can be broken up by a prism into bands of red, orange, yellow, green, blue, indigo and violet.

Blue and red light, which plants absorb, have the greatest effect on plant growth. Blue light is responsible primarily for vegetative (leaf) growth. Red light, when combined with blue light, encourages flowering. Plants look green to us because they reflect, rather than absorb, green light.

Knowing which light source to use is important for manipulating plant growth. For example, fluorescent (cool white) light is high in the blue wavelength. It encourages leafy growth and is excellent for starting seedlings. Incandescent light is high in the red or orange range, but generally produces too much heat to be a valuable light source for plants. Fluorescent grow-lights attempt to imitate sunlight with a mixture of red and blue wavelengths, but they are costly and generally no better than regular fluorescent lights.

Duration, or photoperiod , refers to the amount of time a plant is exposed to light. Photoperiod controls flowering in many plants (Figure 1). Scientists used to think that the length of light period triggered flowering and other responses within plants. Thus, they describe plants as short-day or long-day, depending on what conditions they flower under. We now know that it is not the length of the light period, but rather the length of uninterrupted darkness, that is critical to floral development.

Plants are classified into three categories: short-day (long-night), long-day (short-night), or day-neutral, depending on their response to the duration of light or darkness. Short-day plants form flowers only when day length is less than about 12 hours. Many spring- and fall-flowering plants, such as chrysanthemum, poinsettia and Christmas cactus, are in this category.

In contrast, long-day plants form flowers only when day length exceeds 12 hours. Most summer-flowering plants (e.g., rudbeckia, California poppy and aster), as well as many vegetables (beet, radish, lettuce, spinach and potato), are in this category.

Day-neutral plants form flowers regardless of day length. Examples are tomato, corn, cucumber and some strawberry cultivars. Some plants do not fit into any category, but may respond to combinations of day lengths. Petunias, for example, flower regardless of day length, but flower earlier and more profusely with long days.

Environmental factors that affect plant growth include light, temperature, water, humidity and nutrition.

You can easily manipulate photoperiod to stimulate flowering. For example, chrysanthemums normally flower in the short days of spring or fall, but you can get them to bloom in midsummer by covering them with a cloth that completely blocks out light for 12 hours each day. After several weeks of this treatment, the artificial dark period no longer is needed, and the plants will bloom as if it were spring or fall. This method also is used to make poinsettias flower in time for Christmas.

To bring a long-day plant into flower when day length is less than 12 hours, expose the plant to supplemental light. After a few weeks, flower buds will form.

Temperature

Temperature influences most plant processes, including photosynthesis, transpiration, respiration, germination and flowering. As temperature increases (up to a point), photosynthesis, transpiration and respiration increase. When combined with day length, temperature also affects the change from vegetative (leafy) to reproductive (flowering) growth. Depending on the situation and the specific plant, the effect of temperature can either speed up or slow down this transition.

Germination

The temperature required for germination varies by species. Generally, cool-season crops (e.g., spinach, radish and lettuce) germinate best at 55° to 65°F, while warm-season crops (e.g., tomato, petunia and lobelia) germinate best at 65° to 75°F.

Sometimes horticulturists use temperature in combination with day length to manipulate flowering. For example, a Christmas cactus forms flowers as a result of short days and low temperatures (Figure 1). To encourage a Christmas cactus to bloom, place it in a room with more than 12 hours of darkness each day and a temperature of 50° to 55°F until flower buds form.

If temperatures are high and days are long, cool-season crops such as spinach will flower (bolt). However, if temperatures are too cool, fruit will not set on warm-season crops such as tomato.

Crop quality

Low temperatures reduce energy use and increase sugar storage. Thus, leaving crops such as ripe winter squash on the vine during cool, fall nights increases their sweetness.

Adverse temperatures, however, cause stunted growth and poor-quality vegetables. For example, high temperatures cause bitter lettuce.

Photosynthesis and respiration

Thermoperiod refers to daily temperature change. Plants grow best when daytime temperature is about 10 to 15 degrees higher than nighttime temperature. Under these conditions, plants photosynthesize (build up) and respire (break down) during optimum daytime temperatures and then curtail respiration at night. However, not all plants grow best under the same range between nighttime and daytime temperatures. For example, snapdragons grow best at nighttime temperatures of 55°F; poinsettias, at 62°F.

Temperatures higher than needed increase respiration, sometimes above the rate of photosynthesis. Thus, photosynthates are used faster than they are produced. For growth to occur, photosynthesis must be greater than respiration.

Daytime temperatures that are too low often produce poor growth by slowing down photosynthesis. The result is reduced yield (i.e., fruit or grain production).

Breaking dormancy

Some plants that grow in cold regions need a certain number of days of low temperature (dormancy). Knowing the period of low temperature required by a plant, if any, is essential in getting it to grow to its potential.

Peaches are a prime example; most varieties require 700 to 1,000 hours between 32° and 45°F before breaking their rest period and beginning growth. Lilies need six weeks of temperatures at or slightly below 33°F before blooming.

Daffodils can be forced to flower by storing the bulbs at 35° to 40°F in October. The cold temperature allows the bulbs to mature. When transferred to a greenhouse in midwinter, they begin to grow, and flowers are ready to cut in three to four weeks.

Plants are classified as hardy or nonhardy depending on their ability to withstand cold temperatures. Hardy plants are those that are adapted to the cold temperatures of their growing environment.

Woody plants in the temperate zone have very sophisticated means for sensing the progression from fall to winter. Decreasing day length and temperature trigger hormonal changes that cause leaves to stop photosynthesizing and to ship nutrients to twigs, buds, stems and roots. An abscission layer forms where each petiole joins a stem, and the leaves eventually fall off. Changes within the trunk and stem tissues over a relatively short period of time "freeze-proof" the plant.

Winter injury to hardy plants generally occurs when temperatures drop too quickly in the fall before a plant has progressed to full dormancy. In other cases, a plant may break dormancy in mid- or late winter if the weather is unseasonably warm. If a sudden, severe cold snap follows the warm spell, otherwise hardy plants can be seriously damaged.

It is worth noting that the tops of hardy plants are much more cold-tolerant than the roots. Plants that normally are hardy to 10°F may be killed if they are in containers and the roots are exposed to 20°F.

People often forget that plants need water even during winter.

Winter injury also may occur because of desiccation (drying out) of plant tissues. People often forget that plants need water even during winter. When the soil is frozen, water movement into a plant is severely restricted. On a windy winter day, broadleaf evergreens can become water-deficient in a few minutes, and the leaves or needles then turn brown. To minimize the risk of this type of injury, make sure your plants go into the winter well watered.

Water and humidity

Most growing plants contain about 90 percent water. Water plays many roles in plants. It is:

• A primary component in photosynthesis and respiration
• Responsible for turgor pressure in cells (Like air in an inflated balloon, water is responsible for the fullness and firmness of plant tissue. Turgor is needed to maintain cell shape and ensure cell growth.)
• A solvent for minerals and carbohydrates moving through the plant
• Responsible for cooling leaves as it evaporates from leaf tissue during transpiration
• A regulator of stomatal opening and closing, thus controlling transpiration and, to some degree, photosynthesis
• The source of pressure to move roots through the soil
• The medium in which most biochemical reactions take place

Relative humidity is the ratio of water vapor in the air to the amount of water the air could hold at the current temperature and pressure. Warm air can hold more water vapor than cold air. Relative humidity (RH) is expressed by the following equation:

RH = water in air ÷ water air could hold (at constant temperature and pressure)

Relative humidity is given as a percent. For example, if a pound of air at 75°F could hold 4 grams of water vapor, and there are only 3 grams of water in the air, then the relative humidity (RH) is:

3 ÷ 4 = 0.75 = 75%

Water vapor moves from an area of high relative humidity to one of low relative humidity. The greater the difference in humidity, the faster water moves. This factor is important because the rate of water movement directly affects a plant's transpiration rate.

The relative humidity in the air spaces between leaf cells approaches 100 percent. When a stoma opens, water vapor inside the leaf rushes out into the surrounding air (Figure 2), and a bubble of high humidity forms around the stoma. By saturating this small area of air, the bubble reduces the difference in relative humidity between the air spaces within the leaf and the air adjacent to the leaf. As a result, transpiration slows down.

If wind blows the humidity bubble away, however, transpiration increases. Thus, transpiration usually is at its peak on hot, dry, windy days. On the other hand, transpiration generally is quite slow when temperatures are cool, humidity is high, and there is no wind.

Hot, dry conditions generally occur during the summer, which partially explains why plants wilt quickly in the summer. If a constant supply of water is not available to be absorbed by the roots and moved to the leaves, turgor pressure is lost and leaves go limp.

Plant nutrition

Plant nutrition often is confused with fertilization. Plant nutrition refers to a plant's need for and use of basic chemical elements. Fertilization is the term used when these materials are added to the environment around a plant. A lot must happen before a chemical element in a fertilizer can be used by a plant.

Plants need 17 elements for normal growth. Three of them--carbon, hydrogen and oxygen--are found in air and water. The rest are found in the soil.

Six soil elements are called macronutrients because they are used in relatively large amounts by plants. They are nitrogen, potassium, magnesium, calcium, phosphorus and sulfur.

Eight other soil elements are used in much smaller amounts and are called micronutrients or trace elements. They are iron, zinc, molybdenum, manganese, boron, copper, cobalt and chlorine.

Most of the nutrients a plant needs are dissolved in water and then absorbed by its roots. In fact, 98 percent are absorbed from the soil-water solution, and only about 2 percent are actually extracted from soil particles.

Fertilizers

Fertilizers are materials containing plant nutrients that are added to the environment around a plant. Generally, they are added to the water or soil, but some can be sprayed on leaves. This method is called foliar fertilization . It should be done carefully with a dilute solution, because a high fertilizer concentration can injure leaf cells. The nutrient, however, does need to pass through the thin layer of wax (cutin) on the leaf surface.

Fertilizers are not plant food! Plants produce their own food from water, carbon dioxide and solar energy through photosynthesis. This food (sugars and carbohydrates) is combined with plant nutrients to produce proteins, enzymes, vitamins and other elements essential to growth.

Nutrient absorption

Anything that reduces or stops sugar production in leaves can lower nutrient absorption. Thus, if a plant is under stress because of low light or extreme temperatures, nutrient deficiency may develop.

A plant's developmental stage or rate of growth also may affect the amount of nutrients absorbed. Many plants have a rest (dormant) period during part of the year. During this time, few nutrients are absorbed. Plants also may absorb different nutrients as flower buds begin to develop than they do during periods of rapid vegetative growth.

Was this page helpful?

Related content from osu extension.

Gardening with (and without) slugs and snails

Gardening in what's referred to as a global gastropod biodiversity hotspot (Oregon), means dealing with slugs and snails. There are a variety of ways to help prevent damage to your plants. Here is a collection of resources from OSU Extension. 

May 2024 | Collection

Get Actionable Results from a Soil, Plant or Environmental Testing Lab

Learn how to work with an analytical laboratory to get useful results from your plant tissue, soil or water samples.

Shannon Cappellazzi, Clare Sullivan, Gordon B. Jones, Linda Brewer | Mar 2024 | Extension Catalog publication Peer reviewed (Orange level)

Ivy removal in a home landscape

Linda McMahan tackles ivy and shows how you can remove it from trees and fences.

Linda R. McMahan | Sep 2008 | Article Peer reviewed (Gray level)

Firewise Landscaping Basics

Learn about plants that can help you reduce the risk of fire while also creating an attractive environment. See why landscape maintenance and plant placement are just as critical as plant selection.

Amy Jo Detweiler | May 2024 | Video

Can essential oils control slugs?

I've heard essentials oils may be useful in keeping slugs away from my plants and vegetables. Is this true?

Rory Mc Donnell | May 2024 | Featured question

Slug chat with OSU slug expert Rory McDonnell

Watch the 45-minute lunchtime SLUG CHAT with Associate Professor and Primary Investigator of OSU’s Invertebrate Crop Pest Lab, Rory McDonnell. Dr. McDonnell’s work focuses on understanding the ecology of invasive slugs and snails,...

LeAnn Locher, Rory Mc Donnell | May 2024 | Video

An Educator's Guide to Vegetable Gardening

This publication is a primer on vegetable gardening written specifically for educators, including those who use gardens as part of a nutrition education curriculum. It outlines a full-circle approach to educational ...

Weston Miller, Beret Halverson, Gail Langellotto | Sep 2011 | Extension Catalog publication Peer reviewed (Orange level)

The ABCs of NPK: A fertilizer guide

Nitrogen, phosphorus and potassium aren't just an alphabet soup of chemicals. They are essential plant nutrients that, when used correctly, help to grow a healthy garden. Learn what fertilizers to apply when in this handy guide.

Lisa Ehle | Jun 2018 | Article

What should I be doing in the winter for weed control?

The straw mulch I used at the end of summer to suppress the weeds doesn't seem to be working. Should I till it and cover with plastic? black or clear? Is there something better. Or should I add more straw. I could probably bring some cardboard home from work. Is this a healthy option?

Ann Kinkley | Dec 2017 | Featured question

Will ladybugs ruin my garden?

Can ladybugs kill plants in my vegetable garden?

Steve Renquist | Jul 2014 | Featured question

Slugs and snails, destructors of crops and gardens, could be controlled by bread dough

Bread dough is a nontoxic, generic and effective tool that could be used in the detection and management of gastropods worldwide.

Kym Pokorny | Aug 18, 2021 | News story

Growing Gardens Summit: Part 2

Join Rick "on assignment" as he travels to the Growing School Gardens Summit, in San Diego California. Rick interviews a dozen people with amazing stories. This is part TWO of a four-part series.

Michelle Markesteyn, PhD, MSEL, Rick Sherman | Apr 2024 | Podcast episode Peer reviewed (Gray level)

Can I grow garlic next to my berries?

I am getting prepared to plant my garlic in October or November. I have lots of space around my blueberry plants. Would they survive near each other? Someone told me my blueberries may taste like garlic! Is that possible?

Wei Qiang Yang | Oct 2014 | Featured question

Lincoln County Gardeners Resource Guide

Resources for gardeners in Lincoln County, as prepared by the Lincoln County Master Gardeners.

Stormi Dykes, Cathi Block | Jan 2024 | Article

Now’s the time to plan for cover crops

Cover crops can add organic matter and aerate the soil, protect it from compaction caused by rain, suppress weeds and reduce erosion,

Kym Pokorny | Aug 13, 2021 | News story

Gardening can be accessible to all with some adjustments

“Universal” garden design is planning the landscape so that anyone can access and enjoy it.

Kym Pokorny | May 26, 2023 | News story

Have a question? Ask Extension!

Ask Extension is a way for you to get answers from the Oregon State University Extension Service. We have experts in family and health, community development, food and agriculture, coastal issues, forestry, programs for young people, and gardening.

Testing a Hypothesis—Plant Growth

Charles Darwin believed that there were hereditary advantages in having two sexes for both the plant and animal kingdoms. Some time after he wrote  Origin of Species , he performed an experiment in his garden. He raised two large beds of snapdragons, one from cross-pollinated seeds, the other from self-pollinated seeds. He observed, “To my surprise, the crossed plants when fully grown were plainly taller and more vigorous than the self-fertilized ones.” This led him to another, more time-consuming experiment in which he raised pairs of plants, one of each type, in the same pot and measured the differences in their heights. He had a rather small sample and was not sure that he could safely conclude that the mean of the differences was greater than 0. His data for these plants were used by statistical pioneer R. A. Fisher to illustrate the use of a  t -test.

Looking at Darwin’s Data

1. Open  Darwin.ftm  from the  Tutorial Starters   folder in the  Sample Documents   folder.  This document contains the data for the experiment described above: 1 attribute, 15 cases.

2. Make a case table, a dot plot, and a summary table similar to those shown here.

We see that most of the measurements are greater than 0, meaning that the cross-pollinated plants grew bigger. But two of the measurements are less than 0. Darwin did not feel justified in tossing out these two values and was faced with a very real statistical question.

Formulating a Hypothesis

Darwin’s theory—that cross-pollination produced bigger plants than self-pollination—predicts that, on average, the difference between the two heights should be greater than 0. On the other hand, it might be that his 15 pairs of plants have a mean difference as great as they do (21-eigths of an inch) merely by chance. You can write out these two hypotheses in Fathom in a text object to be stored with your document.

3. From the shelf, drag a text object into the document.

4. Write the null hypothesis and the alternative hypothesis. At right you can  see one way to phrase the hypotheses.

You can choose  Edit | Show Text Palette  to bring up a full suite of tools for formatting text and creating mathematical expressions.

Deciding on a Test Statistic

At the time of Darwin’s experiment, there was no very good theory for dealing with a small sample from a population whose standard deviation is not known. It was not until some years later that William Gosset, a student of Karl Pearson, developed a statistic and its distribution. Gosset published his result under the pseudonym Student, and the statistic became known as Student’s  t . When the null hypothesis is that the mean is 0, the  t -statistic is simply, x ̄/( s /√ n ), where x ̄ is the observed mean,  s  is the sample standard deviation, and  n  is the number of observations.

Let’s compute this statistic for Darwin’s data using one of Fathom’s built-in statistics objects.

5. Drag a test object from the shelf.  An empty test appears.

6. From the pop-up menu, choose  Test Mean .  As shown at right, the Test Mean test allows us to type in summary statistics. The blue text is editable. This is very useful when you don’t have raw data.

7. Try editing the blue text. You can, for example, enter the summary statistics for Darwin’s data.

Here are some things to notice.

• Changing something in one part of the test may affect other parts. For example, editing the AttributeName field in the first line also changes it in the hypothesis line and in the last paragraph.

• In the hypothesis line, clicking on the “is not equal to” phrase brings up a pop-up menu from which we can choose one of three options. For Darwin’s experiment, we want the third option because his hypothesis is that the true mean difference is greater than 0 . Notice that making this change alters the phrasing of the last line of the test as well.

• In addition to simple editing of numbers, we can also determine their value with a formula. For example, we might want to tie the sample count to a slider named n so that we could investigate the effect of different sample sizes. To show the formula editor, choose  Edit | Edit Formula  with the text cursor in the number whose value you wish to determine. These computed values display in gray instead of blue. Editing the value itself deletes the formula.

Checking Assumptions

Gosset’s work with the t -statistic relied on an assumption about the population from which measurements would be drawn, namely, that the values in the population are normally distributed. Is this a reasonable assumption for Darwin’s data?

Height measurements of living things, both plants and animals, are usually normally distributed, and so are differences between heights. But we might worry, because the two negative values give a decidedly skewed appearance to the distribution.

Fathom can help us determine qualitatively whether this amount of skew is unusual. We’ll generate measurements randomly from a normal distribution and compare the results with the original data.

8. Make a new attribute in the collection. Call it  simHeight  for simulated height.

9. Select  simHeight  and choose  Edit | Edit Formula . Enter the formula shown below.

This formula tells Fathom to generate random numbers from a normal distribution whose mean and standard deviation are the same as in our original data. We want to compare the distribution of these simulated heights with the distribution of the original data. We can do that directly in the dot plot that already shows  HeightDifferences .

10. Drop  simHeight  on the plus sign to add it to the horizontal axis.  The graph now shows the original data on top and the simulated data on the bottom.

One set of simulated data doesn’t tell the whole story. We need to look at a bunch.

11. Choose  Collection | Rerandomize .

Each time you rerandomize, you get a new set of 15 values from a population with the same mean and standard deviation as the original 15 measurements. Three examples are shown below.

A bit of subjectivity is called for here. Does it appear that the original distribution is very unusual, or does it fit in with the simulated distributions?

Testing the Hypothesis

Once we have decided that the assumption of normality is met, we can go on to determine whether the  t -statistic for Darwin’s data is large enough to allow us to reject the null hypothesis.

In step 7, we typed the summary values into the test as though we didn’t have the raw data. But we are in the fortunate position of having the raw data, so we can ask Fathom to figure out all the statistics using that data.

12. Drag   HeightDifferences  from the case table to the top pane of the test where it says “Attribute (numeric): unassigned.”

13. If the hypothesis line does not already say “is greater than,” then select that choice from the pop-up menu.

The last paragraph of the test describes the results. If the null hypothesis were true and the experiment were performed repeatedly, the probability of getting a value for Student’s  t  this great or greater would be 0.025. This is a pretty low  P -value, so we can safely reject the null hypothesis and, with Darwin, pursue the theory that cross-pollination increases a plant’s height compared with self-pollination.

Looking at the t -Distribution

It is helpful to be able to visualize the P -value as an area under a distribution.

14. With the test selected, choose  Test | Show Test Statistic Distribution .  The curve shows the probability density for the t -statistic with 14 degrees of freedom. The shaded area shows the portion of the area under the curve to the right of the test statistic for Darwin’s data. We’ve set this up as a one-tailed test; we’re only interested in the mean difference being greater than zero. The total area under the curve is 1, so the area of the shaded portion corresponds to the P -value for Darwin’s experiment.

Let’s investigate how the P -value depends on the test mean, which is currently set to 0.

15. Drag a slider from the shelf into the document.

16. Edit the name of the slider from  V1  to  TestMean .

17. Select the 0 in the statement of the hypothesis in the test. Choose  Edit | Edit Formula .

18. In the formula editor, enter the slider name   TestMe an  and click  OK .

Now the value of the null hypothesis mean in the test and the shaded area under the  t -distribution change to reflect the new hypothesis.

19. Drag the slider slowly and observe the changes that take place.

For what value of the slider is half the area under the curve shaded? Explain why it should be this particular value.

The illustration below shows something similar to what you probably  have. Note that the test has been switched to “nonverbose” (choose  Test | Verbose ).

Going Further

• Play around with changing the data and observing the effect on the P -value. How much closer to 0 can the experimental mean be (without changing the standard deviation) and still have a  P -value greater than 0.05? If you make the standard deviation smaller, what happens to the  P -value (and why)?
• Make a Test Mean object that tests the mean of   simHeight   instead of   HeightDifferences . Notice that each time you rerandomize, you get a new  P -value. Think about what it means when the P -value is greater than 0.05. Would you call this a “false positive” or a “false negative”? By repeatedly rerandomizing, estimate the proportion of the time that the P -value is greater than 0.05. What practical significance would that have in planning an experiment?

How to Grow and Care for Polka Dot Plant

Debra LaGattuta is a Master Gardener with 30+ years of experience in perennial and flowering plants, container gardening, and raised bed vegetable gardening. She is a lead gardener in a Plant-A-Row, which is a program that offers thousands of pounds of organically-grown vegetables to local food banks. Debra is a member of The Spruce Garden Review Board.

• Propagating
• Growing From Seed
• Growing in Pots

Overwintering

• Common Pests
• Common Problems

Polka dot plant  ( Hypoestes phyllostachya ), sometimes called freckle face plant, is an herbaceous warm-climate perennial with brightly variegated leaves . The most common polka dot plants feature green foliage flecked with pink, but varieties with purple, white, or red variegation are also available. Polka dot plant grows best in warm, humid conditions with bright, indirect light or partial shade.

The Spruce / Leticia Almeida

Polka dot plants are easy to grow with the proper conditions. They have a moderate growth rate and remain relatively small once mature, especially when grown indoors as houseplants. Because they are native to warm climates, many gardeners treat them as annuals when planted outdoors. Polka dot plants are not considered invasive plants in temperate climates, but they are considered invasive in Australia and some other tropical areas, including Hawaii.

The Spruce / Photo Illustration by Amy Sheehan / Leti­cia Almeida

Polka Dot Plant Care

• Plant polka dot plant in rich, well-drained potting mix.
• Place polka dot plants in a warm location with bright, indirect light indoors or part sun outdoors.
• Water your polka dot plant when the top half-inch of soil has dried out.
• Fertilize plants once per month during spring and summer.
• Polka dot plants complete their growth cycle after flowering, giving them a lifespan of one to two years in most environments.

Polka dot plants have become a problematic, aggressive grower in Queensland and New South Wales, Australia. In the continental US, the plant is not considered invasive and is safe to plant in-ground.

Outdoors, plant polka dot plants in a location that receives some shade. Too much light can cause the plant's variegation to fade. Bright, indirect light from an east- or south-facing window is ideal indoors. 

Polka dot plants prefer soil rich in organic matter with good drainage. An all-purpose organic potting mix is typically suitable for these plants. Mix in some pumice or perlite to improve soil drainage.

Keep the soil evenly moist. Water the plant when the top half-inch of soil has dried out. Cut back slightly on watering in the winter, then resume watering once you see new growth appear in the spring.

Temperature and Humidity

Keep your polka dot plant in a warm place with at least 50 percent humidity. They can be a great bathroom plant , if your bathroom has a window. Polka dot plants prefer temperatures over 60 degrees Fahrenheit, so they're only hardy outdoors in USDA growing zones 10 and 11. Move container plants outdoors in the spring after any danger of frost has passed, then bring them back indoors well before the first frost in fall if you plan to overwinter them.

Feed container plants with an organic fertilizer designed for houseplants once a month during the warm growing season. If planting in-ground, mix organic compost into the soil each spring before planting.

Want more gardening tips? Sign up for our free gardening newsletter for our best-growing tips, troubleshooting hacks, and more!

Types of Polka Dot Plants

Different varieties of Hypoestes phyllostachya are bred for their leaf coloration, including:

• ‘Carmina’: has dark green and red-spotted leaves
• ‘Confetti’: offers green leaves with spots of white, pink, rose, red, or burgundy
• ‘Pink Brocade’: features green leaves with mottled pink spots
• ‘Splash’ series: boasts leaves in mixes of greens with splotches of pinks, reds, or whites

Cut or pinch back the top two leaves on each stem every week to promote bushier growth and keep your polka dot plant from becoming leggy . When the plant flowers, clip off the flower spike with clean, sharp shears because the plant will enter dormancy after it flowers. Removing the flowers prevents the plant from going into dormancy.

Pruning Tip

Not sure where to find the best pruners for your polka dot plant? We tested the best pruners on the market, whether you're looking for adjustable pruners, heavy duty, pruners for small hands, and more.

Propagating Polka Dot Plants

You can propagate polka dot plants from stem cuttings . You'll have the most success in spring or summer. Here's how to propagate your polka dot plant from a stem cutting rooted in water. You'll need a small glass or jar and clean, sharp pruners or scissors.

• Cut a stem tip from the mother plant. Make sure it's at least two and ideally four inches long. Remove the leaves on the lower half of the stem.
• Put the cutting in the glass or jar. Add water so that the lower portion of the stem is submerged.
• Put the cutting in a warm place with bright, indirect light. Top off the water to keep the level consistent, and change the water every two weeks or so to keep algae from forming.
• When roots are about two inches long, the cutting is ready to pot up in soil. This can take anywhere from a few weeks to a few months.

How to Grow Polka Dot Plant From Seed

Sow seeds on the surface of warm, moist soil in early spring. Place the plant in a sunny location. The seeds should sprout in a few days. Once the seedling has grown several inches—usually in a couple of weeks—it is ready to transplant into a larger container or plant outdoors. Only plant outdoors after the threat of frost is over.

Potting and Repotting Polka Dot Plant

The best time to repot a polka dot plant is in the spring after its winter dormant period. Your polka dot plant is pot bound when the roots start growing out of the drainage holes in its container. The new pot should be no more than two inches wider and deeper than the old pot. Avoid terra cotta pots, which wick away moisture and can cause the soil to dry out too quickly.

Bring outdoor container plants indoors before night temperatures drop below 60 degrees Fahrenheit in late summer or early fall. You can bring them outdoors again the following spring when night temperatures are consistently above 60 degrees.

Common Pests and Plant Diseases

Pests like mealybugs ,  aphids , and whiteflies can affect polka dot plants. Typical diseases associated with polka dot plants are root rot, leaf-spot diseases, and powdery mildew. Telltale signs of infestations or disease include discolored or damaged foliage and insects crawling or feeding on leaves and stems.

How to Get Polka Dot Plant to Bloom

Unlike most flowering plants, gardeners typically want to prevent polka dot plant from blooming because flowering causes the plant to go dormant. If you want your plant to last longer, it's best to clip off the flower spike when it forms.

Bloom Months

Polka dot plants typically bloom in late summer or early fall as days begin to shorten.

What Do Polka Dot Plant Flowers Look and Smell Like?

Polka dot plants bloom by sending up a small spike with tiny pink or purple flowers. They're not showy or aromatic.

Common Problems With Polka Dot Plants

Leaves losing their color.

Fading leaf color is typically caused by too much or too little sun. Polka dot plants need bright, indirect light to maintain their color, but hot, direct sun can cause variegation to fade.

Leaves Turning Brown or Drooping

Insufficient water and humidity can cause the polka dot plant's leaves to turn brown or start drooping. Also, too much sunlight can burn the leaves. Hard water and overfertilization are other reasons for a polka dot plant's leaves turning brown. Adjust your humidity or watering habits to revive the plant.

Leaves Turning Yellow or Dropping Off

Overwatering can cause leaves to yellow and even drop. If you notice yellowing, reduce the amount of water you give the plant and make sure you're using potting soil with good drainage.

Polka dot plants can be grown indoors, and outdoors in the right climates. If you live in USDA Hardiness Zones 10 through 11, you can grow polka dot plant outdoors.

Polka dot plants will grow best in a warm, humid place with bright, indirect light or dappled sunlight.

Polka dot plants do not spread very much. Polka dot plants usually grow to 16 to 22 inches tall and 18 to 24 inches wide.

Polka dot plants don't always flower, but when they do, it's in the summer months. Their flowers are small and typically lilac or pink in color.

Jon VanZile was a writer for The Spruce covering houseplants and indoor gardening for almost a decade. He is a professional writer whose articles on plants and horticulture have appeared in national and regional newspapers and magazines.

Polka Dot Plant . Brisbane City Council Weed Identification.

Hypoestes phyllostachya. PlantPono.org.

Polka Dot Plant,  Hypoestes phyllostachya . University of Wisconsin, Extension of Horticulture.

More from The Spruce

• Growing Ficus Ruby Can Add a Pop of Color to Your Home—Here's How
• How to Grow and Care for an Urn Plant Like a Pro
• How to Grow Guzmania Bromeliads for Perfect Blooms At Home
• 25 Cat-Safe Plants That Grow Well In Low-Light Conditions
• Why Your Polka Dot Plant Is Leggy and How to Fix It
• 26 Indoor Plants Safe for Cats and Dogs
• How to Grow and Care for Coffee Plant
• How to Grow and Care for Peperomia Plants
• How to Grow and Care for Ti Plant (Good Luck Plant)
• Inch Plant Is One of the Easiest Houseplants to Grow—Here's How to Do It
• How to Grow and Care for Begonias
• How to Grow and Care for the African Spear Plant
• How to Grow and Care for Alocasia
• How to Grow & Care for Alocasia Polly
• How to Grow and Care for Ficus Shivereana
• How to Grow and Care for Corn Plant (Dracaena)