Changes in the photosynthesis properties and photoprotection capacity in rice (Oryza sativa) grown under red, blue, or white light

Comparative analysis of the effects of microplastics and nitrogen on maize and wheat: Growth, redox homeostasis, photosynthesis, and AsA-GSH cycle

Microplastics (MPs) pose a significant threat to the function of agro-ecosystems. At present, research on MPs has mainly focused on the effects of different concentrations or types of MPs on a crop, while ignoring other environmental factors. In agricultural production, the application of nitrogen (N) fertilizer is an important means to maintain the high yield of crops. The effects of MPs and N on growth parameters, photosynthetic system, active oxygen metabolism, nutrient content, and ascorbate-glutathione (AsA-GSH) cycle of maize and wheat were studied in order to explicit whether N addition could effectively alleviate the effects of MPs on maize and wheat. The results showed that MPs inhibited the plant height of both maize and wheat, and MPs effects on physiological traits of maize were more severe than those of wheat, reflecting in reactive oxygen metabolism and restriction of photosynthetic capacity. Under the condition of N supply, AsA-GSH cycle of two plants has different response strategies to MPs: Maize promoted enzyme activity and co-accumulation of AsA and GSH, while wheat tended to consume AsA and accumulate GSH. N application induced slight oxidative stress on maize, which was manifested as an increase in hydrogen peroxide and malonaldehyde contents, and activities of polyphenol oxidase and peroxidase. The antioxidant capacity of maize treated with the combination of MPs + N was better than that treated with N or MPs alone. N could effectively alleviate the adverse effects of MPs on wheat by improving the antioxidant capacity.

From leaf to multiscale models of photosynthesis: applications and challenges for crop improvement

To keep up with the growth of human population and to circumvent deleterious effects of global climate change, it is essential to enhance crop yield to achieve higher production. Here we review mathematical models of oxygenic photosynthesis that are extensively used, and discuss in depth a subset that accounts for diverse approaches providing solutions to our objective. These include models (1) to study different ways to enhance photosynthesis, such as fine-tuning antenna size, photoprotection and electron transport; (2) to bioengineer carbon metabolism; and (3) to evaluate the interactions between the process of photosynthesis and the seasonal crop dynamics, or those that have included statistical whole-genome prediction methods to quantify the impact of photosynthesis traits on the improvement of crop yield. We conclude by emphasizing that the results obtained in these studies clearly demonstrate that mathematical modelling is a key tool to examine different approaches to improve photosynthesis for better productivity, while effective multiscale crop models, especially those that also include remote sensing data, are indispensable to verify different strategies to obtain maximized crop yields.

Creating a new yellow and blue combination transparent film for Panax ginseng C.A. Meyer growth based on orthogonal designs

Panax ginseng C.A. Meyer originates from old-growth forest environments, where the light intensity and spectrum reaching the forest bed are influenced by the canopy and humidity. In farmlands, suitable light intensity for cultivation is achieved by controlling the light transmission rate using shading nets, while light quality is regulated by a cover of yellow or blue transparent film. Such films have a light quality distinct from that produced by old-growth forests. Herein, a large composite film was developed by alternating small pieces of yellow and blue transparent film. An orthogonal array was used to evaluate the influence of the small transparent film area (STFA), yellow transparent film (YTF) number, and blue transparent film (BTF) number on the associated changes in ginseng in a range of fluorescence-, photosynthesis-, morphology-, and crop quality-related factors. Our results showed that light intensity was influenced primarily by STFA, which caused an overall decrease, while the light quality ratio was affected primarily by YTF number, which increased the proportion of red light and decreased that of blue light, with corresponding influence on different growth parameters. Based on these observations, an improved yellow and blue combination transparent film (YBCTF) with the following characteristics was established: STFA: 15 × 15 cm, YTF: two pieces, and BTF: three pieces. The improved YBCTF facilitated efficient light energy use by the plants, and led to an increase in leaf area, the per leaf photosynthetic rate, dry root weight, and the per root single ginsenoside yield. The findings present a relatively low-cost approach for optimising the light environment of ginseng cultivated in farmland and other crops in large-scale agricultural settings.

Dynamic Analysis of Chlorophyll a Fluorescence in Response to Time-Variant Excitations during Strong Actinic Illumination and Application in Probing Plant Water Loss

Magnitude measurement of chlorophyll a fluorescence (ChlF) involves challenges, and dynamic responses to variable excitations may offer an alternative. In this research, ChlF was measured during strong actinic light by using a pseudo-random binary sequence as a time-variant multiple-frequency illumination excitation. The responses were observed in the time domain but were primarily analyzed in the frequency domain in terms of amplitude gain variations. The excitation amplitude was varied, and moisture loss was used to induce changes in the plant samples for further analysis. The results show that when nonphotochemical quenching (NPQ) activities start, the amplitude of ChlF responses vary, making the ChlF responses to illumination excitations nonlinear and nonstationary. NPQ influences the ChlF responses in low frequencies, most notably below 0.03 rad/s. The low-frequency gain is linearly correlated with NPQ and can thus be used as a reference to compensate for the variations in ChlF measurements. The high-frequency amplitude gain showed a stronger correlation with moisture loss after correction with the low-frequency gain. This work demonstrates the usefulness of dynamic characteristics in broadening the applications of ChlF measurements in plant analysis and offers a way to mitigate variabilities in ChlF measurements during strong actinic illumination.

Mechanistic Approach on Melatonin-Induced Hormesis of Photosystem II Function in the Medicinal Plant Mentha spicata

Melatonin (MT) is considered a new plant hormone having a universal distribution from prokaryotic bacteria to higher plants. It has been characterized as an antistress molecule playing a positive role in the acclimation of plants to stress conditions, but its impact on plants under non-stressed conditions is not well understood. In the current research, we evaluated the impact of MT application (10 and 100 μM) on photosystem II (PSII) function, reactive oxygen species (ROS) generation, and chlorophyll content on mint (Mentha spicata L.) plants in order to elucidate the molecular mechanism of MT action on the photosynthetic electron transport process that under non-stressed conditions is still unclear. Seventy-two hours after the foliar spray of mint plants with 100 μM MT, the improved chlorophyll content imported a higher amount of light energy capture, which caused a 6% increase in the quantum yield of PSII photochemistry (ΦPSII) and electron transport rate (ETR). Nevertheless, the spray with 100 μM MT reduced the efficiency of the oxygen-evolving complex (OEC), causing donor-side photoinhibition, with a simultaneous slight increase in ROS. Even so, the application of 100 μM MT decreased the excess excitation energy at PSII implying superior PSII efficiency. The decreased excitation pressure at PSII, after 100 μM MT foliar spray, suggests that MT induced stomatal closure through ROS production. The response of ΦPSII to MT spray corresponds to a J-shaped hormetic curve, with ΦPSII enhancement by 100 μM MT. It is suggested that the hormetic stimulation of PSII functionality was triggered by the non-photochemical quenching (NPQ) mechanism that stimulated ROS production, which enhanced the photosynthetic function. It is concluded that MT molecules can be used under both stress and non-stressed conditions as photosynthetic biostimulants for enhancing crop yields.

Growth Light Quality Influences Leaf Surface Temperature by Regulating the Rate of Non-Photochemical Quenching Thermal Dissipation and Stomatal Conductance

Significant efforts have been made to optimise spectrum quality in indoor farming to maximise artificial light utilisation and reduce water loss. For such an improvement, green (G) light supplementation to a red-blue (RB) background was successfully employed in our previous studies to restrict both non-photochemical quenching (NPQ) and stomatal conductance (gs). At the same time, however, the downregulation of NPQ and gs had the opposite influence on leaf temperature (Tleaf). Thus, to determine which factor plays the most prominent role in Tleaf regulation and whether such a response is temporal or permanent, we investigated the correlation between NPQ and gs and, subsequently, Tleaf. To this end, we analysed tomato plants (Solanum lycopersicum L. cv. Malinowy Ozarowski) grown solely under monochromatic LED lamps (435, 520, or 662 nm; 80 µmol m-2 s-1) or a mixed RGB spectrum (1:1:1; 180 µmol m-2 s-1) and simultaneously measured gs and Tleaf with an infrared gas analyser and a thermocouple or an infrared thermal camera (FLIR) during thermal imaging analyses. The results showed that growth light quality significantly modifies Tleaf and that such a response is not temporal. Furthermore, we found that the actual adaxial leaf surface temperature of plants is more closely related to NPQ amplitude, while the temperature of the abaxial surface corresponds to gs.

Modification of Tomato Photosystem II Photochemistry with Engineered Zinc Oxide Nanorods

We recently proposed the use of engineered irregularly shaped zinc oxide nanoparticles (ZnO NPs) coated with oleylamine (OAm), as photosynthetic biostimulants, to enhance crop yield. In the current research, we tested newly engineered rod-shaped ZnO nanorods (NRs) coated with oleylamine (ZnO@OAm NRs) regarding their in vivo behavior related to photosynthetic function and reactive oxygen species (ROS) generation in tomato (Lycopersicon esculentum Mill.) plants. ZnO@OAm NRs were produced via solvothermal synthesis. Their physicochemical assessment revealed a crystallite size of 15 nm, an organic coating of 8.7% w/w, a hydrodynamic diameter of 122 nm, and a ζ-potential of -4.8 mV. The chlorophyll content of tomato leaflets after a foliar spray with 15 mg L-1 ZnO@OAm NRs presented a hormetic response, with an increased content 30 min after the spray, which dropped to control levels 90 min after the spray. Simultaneously, 90 min after the spray, the efficiency of the oxygen-evolving complex (OEC) decreased significantly (p < 0.05) compared to control values, with a concomitant increase in ROS generation, a decrease in the maximum efficiency of PSII photochemistry (Fv/Fm), a decrease in the electron transport rate (ETR), and a decrease in the effective quantum yield of PSII photochemistry (ΦPSII), indicating reduced PSII efficiency. The decreased ETR and ΦPSII were due to the reduced efficiency of PSII reaction centers (Fv'/Fm'). There were no alterations in the excess excitation energy at PSII or the fraction of open PSII reaction centers (qp). We discovered that rod-shaped ZnO@OAm NRs reduced PSII photochemistry, in contrast to irregularly shaped ZnO@OAm NPs, which enhanced PSII efficiency. Thus, the shape and organic coating of the nanoparticles play a critical role in the mechanism of their action and their impact on crop yield when they are used in agriculture.

Impact of Coated Zinc Oxide Nanoparticles on Photosystem II of Tomato Plants

Zinc oxide nanoparticles (ZnO NPs) have emerged as a prominent tool in agriculture. Since photosynthetic function is a significant measurement of phytotoxicity and an assessment tool prior to large-scale agricultural applications, the impact of engineered irregular-shaped ZnO NPs coated with oleylamine (ZnO@OAm NPs) were tested. The ZnO@OAm NPs (crystalline size 19 nm) were solvothermally prepared in the sole presence of oleylamine (OAm) and evaluated on tomato (Lycopersicon esculentum Mill.) photosystem II (PSII) photochemistry. Foliar-sprayed 15 mg L-1 ZnO@OAm NPs on tomato leaflets increased chlorophyll content that initiated a higher amount of light energy capture, which resulted in about a 20% increased electron transport rate (ETR) and a quantum yield of PSII photochemistry (ΦPSII) at the growth light (GL, 600 μmol photons m-2 s-1). However, the ZnO@OAm NPs caused a malfunction in the oxygen-evolving complex (OEC) of PSII, which resulted in photoinhibition and increased ROS accumulation. The ROS accumulation was due to the decreased photoprotective mechanism of non-photochemical quenching (NPQ) and to the donor-side photoinhibition. Despite ROS accumulation, ZnO@OAm NPs decreased the excess excitation energy of the PSII, indicating improved PSII efficiency. Therefore, synthesized ZnO@OAm NPs can potentially be used as photosynthetic biostimulants for enhancing crop yields after being tested on other plant species.

Photomorphogenesis and Photosynthetic Traits Changes in Rice Seedlings Responding to Red and Blue Light

The purpose of this study is to determine the effects of red and blue lights on the photomorphogenesis and photosynthetic traits of rice seedlings. The rice seedlings were cultured with red light (R), blue light (B), combined red and blue lights (R3B1/R1B1/R1B3), and white light (CK) as the control. The combined application of red and blue lights could promote the growth of rice seedlings to varying degrees; enhance photosynthesis by increasing the seedling leaf area, chlorophyll content, and chlorophyll fluorescence; improve root characteristics by increasing root number, root volume, and root activity; and thus increase the dry matter accumulation of rice seedlings. In addition, the combination of red and blue lights could regulate the expression of genes related to photosynthesis in rice leaves, affect the activity of the Rubisco enzyme, and then affect the photosynthesis of rice seedlings. These results indicate that red and blue lights have direct synergistic effects, which can regulate the growth of rice seedlings and promote the morphogenesis of rice seedlings. The combined application of red and blue lights can be used to supplement the light in rice-factory seedling raising.

Simultaneous Application of Red and Blue Light Regulate Carbon and Nitrogen Metabolism, Induces Antioxidant Defense System and Promote Growth in Rice Seedlings under Low Light Stress

The purpose of this study is to determine the effect of light quality on growth, carbon and nitrogen metabolism, and antioxidant defense system of rice seedlings. Six light conditions were employed, including white (W), red (R), blue (B), combined LED of R and B at 3:1 (R3B1), combined LED of R and B at 1:1 (R1B1), as well as combined LED of R and B at 1:3 (R1B3). Combined application of red light and blue light could promote the growth of rice seedling leaves and roots under low light stress to varying degrees, increase the photosynthetic area by increasing the leaf area, improve the root characteristics by increasing the root volume, and increase the dry matter accumulation of rice seedlings. In addition, the combination of red light and blue light could increase carbon and nitrogen metabolites in rice seedling leaves, regulate the expression of genes related to carbon and nitrogen metabolism and enzyme activity, and enhance the antioxidant enzyme activity of rice seedlings. These results indicate that red light and blue light directly have synergistic effects which can regulate the carbon and nitrogen metabolism of rice seedlings, promote the morphogenesis of rice seedlings under low light stress, and promote growth, which has never been reported in previous studies. This study is a new discovery in the application of light quality in crop production and provides new avenues to enhance crop stress resistance. However, further study is needed to explore the physio-biochemical and molecular mechanisms of light quality in crop production.

Effects of White and Blue-Red Light on Growth and Metabolism of Basil Grown under Microcosm Conditions

Indoor farming of basil (Ocimum basilicum L.) under artificial lighting to support year-round produce demand is an area of increasing interest. Literature data indicate that diverse light regimes differently affect downstream metabolic pathways which influence basil growth, development and metabolism. In this study, basil was grown from seedlings to fully developed plants in a microcosm, an innovative device aimed at growing plants indoor as in natural conditions. Specifically, the effects of white (W) and blue-red (BR) light under a photosynthetic photon flux density of 255 μmol m^-2 s^-1 on plant growth, photochemistry, soluble nutrient concentration and secondary metabolism were investigated. Plants grew taller (41.8 ± 5.0 vs. 28.4 ± 2.5 cm) and produced greater biomass (150.3 ± 24.2/14.7 ± 2.0 g vs. 116.2 ± 28.3/12.3 ± 2.5 g fresh/dry biomass) under W light compared to BR light. The two lighting conditions differently influenced the soluble nutrient concentration and the translocation rate. No photosynthetic stress was observed under the two lighting regimes, but leaves grown under W light displayed higher levels of maximum quantum yield of PSII and electron transport rate. Sharp differences in metabolic patterns under the two lighting regimes were detected with higher concentrations of phenolic compounds under the BR light.

Data-Independent Acquisition Proteomics Reveals the Effects of Red and Blue Light on the Growth and Development of Moso Bamboo (Phyllostachys edulis) Seedlings

Moso bamboo is a rapidly growing species with significant economic, social, and cultural value. Transplanting moso bamboo container seedlings for afforestation has become a cost-effective method. The growth and development of the seedlings is greatly affected by the quality of light, including light morphogenesis, photosynthesis, and secondary metabolite production. Therefore, studies on the effects of specific light wavelengths on the physiology and proteome of moso bamboo seedlings are crucial. In this study, moso bamboo seedlings were germinated in darkness and then exposed to blue and red light conditions for 14 days. The effects of these light treatments on seedling growth and development were observed and compared through proteomics analysis. Results showed that moso bamboo has higher chlorophyll content and photosynthetic efficiency under blue light, while it displays longer internode and root length, more dry weight, and higher cellulose content under red light. Proteomics analysis reveals that these changes under red light are likely caused by the increased content of cellulase CSEA, specifically expressed cell wall synthetic proteins, and up-regulated auxin transporter ABCB19 in red light. Additionally, blue light is found to promote the expression of proteins constituting photosystem II, such as PsbP and PsbQ, more than red light. These findings provide new insights into the growth and development of moso bamboo seedlings regulated by different light qualities.

The red/blue light ratios from light-emitting diodes affect growth and flower quality of Hippeastrum hybridum 'Red Lion'

Light quality strongly impacts the growth and flower quality of ornamental plants. The optimum light quality for the growth and flowering of Hippeastrum remains to be validated. In the present study, we investigated the effect of the red/blue light ratio of LEDs on the growth and flowering quality of H. hybrid 'Red Lion'. Two LEDs with red/blue light ratio of 1:9 (R₁₀B₉₀) and 9:1 (R₉₀B₁₀) were designed. LEDs of white light were the control. In the earlier vegetative and reproductive growth phase, R₉₀B₁₀ increased the biomass of the bulbs, leaves, and flowers. Compared with the control and R₁₀B₉₀ group, R₉₀B₁₀ LEDs delayed flowering by 2.30 d and 3.26 d, respectively. Based on chlorophyll contents, photosynthetic capacity, chlorophyll fluorescence parameters, and carbohydrate contents, the photosynthesis rate was higher in the R₁₀B₉₀ group. Optimal red and blue light intensity promoted the accumulation of carbohydrates and early flowering and prolonged the flowering period of H. hybrid. Microscopic analysis showed that stomatal density was high, and the number of chloroplasts was large in the R₁₀B₉₀ treatment group, which enhanced photosynthesis. Particularly, R₁₀B₉₀ promoted the expression of seven key genes related to chlorophyll synthesis. R₁₀B₉₀ also promoted early overexpression of the HpCOL gene that promotes early flowering. Thus, higher blue light and 10% red light intensities promote early and extended flowering, while higher red light and 10% blue light promote vegetative plant growth but delay flowering.

Light quality as a driver of photosynthetic apparatus development

Light provides energy for photosynthesis and also acts as an important environmental signal. During their evolution, plants acquired sophisticated sensory systems for light perception and light-dependent regulation of their growth and development in accordance with the local light environment. Under natural conditions, plants adapted by using their light sensors to finely distinguish direct sunlight and dark in the soil, deep grey shade under the upper soil layer or litter, green shade under the canopy and even lateral green reflectance from neighbours. Light perception also allows plants to evaluate in detail the weather, time of day, day length and thus the season. However, in artificial lighting conditions, plants are confronted with fundamentally different lighting conditions. The advent of new light sources - light-emitting diodes (LEDs), which emit narrow-band light - allows growing plants with light of different spectral bands or their combinations. This sets the task of finding out how light of different quality affects the development and functioning of plants, and in particular, their photosynthetic apparatus (PSA), which is one of the basic processes determining plant yield. In this review, we briefly describe how plants perceive environment light signals by their five families of photoreceptors and by the PSA as a particular light sensor, and how they use this information to form their PSA under artificial narrow-band LED-based lighting of different spectral composition. We consider light regulation of the biosynthesis of photosynthetic pigments, photosynthetic complexes and chloroplast ATP synthase function, PSA photoprotection mechanisms, carbon assimilation reactions and stomatal development and function.

Light Quality Modulates Photosynthesis and Antioxidant Properties of B. vulgaris L. Plants from Seeds Irradiated with High-Energy Heavy Ions: Implications for Cultivation in Space

Beta vulgaris L. is a crop selected for cultivation in Space for its nutritional properties. However, exposure to ionizing radiation (IR) can alter plant photosynthetic performance and phytochemical production in the extraterrestrial environment. This study investigated if plant growth under different light quality regimes (FL—white fluorescent; RGB—red–green–blue; RB—red–blue) modifies the photosynthetic behavior and bioactive compound synthesis of plants sprouted by dry seeds irradiated with carbon or titanium high-energy ions. The study evidenced that: (i) the plant response depends on the type of heavyion; (ii) control and C-ion-irradiated plants were similar for photosynthetic pigment content and PSII photochemical efficiency, regardless of the LQ regime; (iii) under FL, net photosynthesis (A_N) and water use efficiency (iWUE) declined in C- and Ti-ion plants compared to control, while the growth of irradiated plants under RGB and RB regimes offset these differences; (iv) the interaction Ti-ion× RB improved iWUE, and stimulated the production of pigments, carbohydrates, and antioxidants. The overall results highlighted that the cultivation of irradiated plants under specific LQ regimes effectively regulates photosynthesis and bioactive compound amounts in leaf edible tissues. In particular, the interaction Ti-ion × RB improved iWUE and increased pigments, carbohydrates, and antioxidant content.

Photoprotection Differences between Dominant Tree Species at Mid- and Late-Successional Stages in Subtropical Forests in Different Seasonal Environments

Plants growing in subtropical regions are often affected by high temperature and high light in summer and low temperature and high light in winter. However, few studies have compared the photoprotection mechanism of tree species at different successional stages in these two environments, although such studies would be helpful in understanding the succession of forest communities in subtropical forests. In order to explore the strategies used by dominant species at different successional stages to cope with these two environmental conditions, we selected two dominant species in the mid-successional stage, Schima superba and Castanopsis chinensis, and two dominant species in the late-successional stage, Machilus chinensis and Cryptocarya chinensis. The cell membrane permeability, chlorophyll fluorescence, chlorophyll content, and a few light-protective substances of these dominant species were measured in summer and winter. The results show that in summer, the young leaves of dominant species in the mid-successional stage showed higher anthocyanin content and superoxide dismutase (SOD) activity, while those in the late-successional stage showed higher flavonoid and total phenolic content, total antioxidant activity, non-photochemical quenching (NPQ), and carotenoid/chlorophyll (Car/Chl) ratio. In winter, young leaves of dominant species in the mid-successional stage were superior to those in the late-successional stage only in terms of catalase (CAT) activity and NPQ, while the anthocyanin, flavonoids, and total phenol content, total antioxidant capacity, and Car/Chl ratio were significantly lower compared to the late-successional stage. Our results show that the dominant species in different successional stages adapted to environmental changes in different seasons through the alterations in their photoprotection strategies. In summer, the dominant species in the mid-successional stage mainly achieved photoprotection through light shielding and reactive-oxygen-species scavenging by SOD, while the antioxidant capacity of trees in the late-successional stage mainly came from an increased antioxidative compounds and heat dissipation. In winter, the dominant species in the mid-successional stage maintained their photoprotective ability mainly through the scavenging of reactive oxygen species by CAT and the heat dissipation provided by NPQ, while those in the late-successional stage were mainly protected by a combination of processes, including light shielding, heat dissipation, and antioxidant effects provided by enzymatic and non-enzymatic antioxidant systems. In conclusion, our study partially explains the mechanism of community succession in subtropical forests.

LED spectral quality and NaCl salinity interact to affect growth, photosynthesis and phytochemical production of Mesembryanthemum crystallinum

The edible halophyte Mesembryanthemum crystallinum L. was grown at different NaCl salinities under different combined red and blue light-emitting diode (LED) light treatments. High salinity (500 mM NaCl) decreased biomass, leaf growth, and leaf water content. Interactions between LED ratio and salinity were detected for shoot biomass and leaf growth. All plants had F v /F m ratios close to 0.8 in dark-adapted leaves, suggesting that they were all healthy with similar maximal efficiency of PSII photochemistry. However, measured under the actinic light near or above the growth light, the electron transport rate (ETR) and photochemical quenching (qP) of M. crystallinum grown at 100 and 250 mM NaCl were higher than at 500 mM NaCl. Grown under red/blue LED ratios of 0.9, M. crystallinum had higher ETR and qP across all salinities indicating higher light energy utilisation. Crassulacean acid metabolism (CAM) was induced in M. crystallinum grown at 500 mM NaCl. CAM-induced leaves had much higher non-photochemical quenching (NPQ), suggesting that NPQ can be used to estimate CAM induction. M. crystallinum grown at 250 and 500 mM NaCl had higher total chlorophyll and carotenoids contents than at 100 mM NaCl. Proline, total soluble sugar, ascorbic acid, and total phenolic compounds were higher in plants at 250 and 500 mM NaCl compared with those at 100 mM NaCl. An interaction between LED ratio and salinity was detected for proline content. Findings of this study suggest that both salinity and light quality affect productivity, photosynthetic light use efficiency, and proline accumulation of M. crystallinum .

Growth, Fruit Yield, and Bioactive Compounds of Cherry Tomato in Response to Specific White-Based Full-Spectrum Supplemental LED Lighting

Supplemental artificial light in greenhouses is fundamental to achieving sustainable crop production with high yield and quality. This study’s purpose was to investigate the efficacy of supplemental light (SL) sources on the vegetative and reproductive growth of cherry tomatoes. Four types of light sources were applied, including high-pressure sodium lamps (HPS), a narrow-spectrum LED light (NSL), and two specific full-spectrum LED lights (SFL1 and SFL2) with a shorter blue peak wavelength (436 nm) and/or green peak wavelength (526 nm). The control was the natural light condition. Shoot fresh and dry weight and leaf area in the SFL1 and SFL2 treatments were greater than those in the control. The HPS and NSL treatments also enhanced tomato growth, but they were less efficient compared to the SFL treatments. The SFL1 and SFL2 treatments showed higher fruit yields by 73.1% and 70.7%, respectively, than the control. The SL sources did not affect the effective photochemical quantum yield of photosystem II (Y (II)). However, they did trigger the increased electron transport rate (ETR) and non-photochemical quenching (NPQ). The SFL treatments enhanced tomato growth, fruit yield, and efficient use of light and energy, suggesting that the specific full spectrum based on the short-wavelength blue and/or green peak can be successfully applied for the cultivation of cherry tomato and other crops in greenhouses.

Effects of partial replacement of red by green light in the growth spectrum on photomorphogenesis and photosynthesis in tomato plants

The artificial light used in growth chambers is usually devoid of green (G) light, which is considered to be less photosynthetically efficient than blue (B) or red (R) light. To verify the role of G light supplementation in the spectrum, we modified the RB spectrum by progressively replacing R light with an equal amount of G light. The tomato plants were cultivated under 100 µmol m^-2 s^-1 of five different combinations of R (35-75%) and G light (0-40%) in the presence of a fixed proportion of B light (25%) provided by light-emitting diodes (LEDs). Substituting G light for R altered the plant's morphology and partitioning of biomass. We observed a decrease in the dry biomass of leaves, which was associated with increased biomass accumulation and the length of the roots. Moreover, plants previously grown under the RGB spectrum more efficiently utilized the B light that was applied to assess the effective quantum yield of photosystem II, as well as the G light when estimated with CO₂ fixation using RB + G light-response curves. At the same time, the inclusion of G light in the growth spectrum reduced stomatal conductance (g_s), transpiration (E) and altered stomatal traits, thus improving water-use efficiency. Besides this, the increasing contribution of G light in place of R light in the growth spectrum resulted in the progressive accumulation of phytochrome interacting factor 5, along with a lowered level of chalcone synthase and anthocyanins. However, the plants grown at 40% G light exhibited a decreased net photosynthetic rate (P_n), and consequently, a reduced dry biomass accumulation, accompanied by morphological and molecular traits related to shade-avoidance syndrome.

Photosynthetic efficiency, growth and secondary metabolism of common buckwheat (Fagopyrum esculentum Moench) in different controlled-environment production systems

Light-emitting diodes (LEDs) and high-pressure sodium lamps (HPS) are among the most commonly used light sources for plant cultivation. The objective of this study was to evaluate the effect of two controlled-environment production systems differing in light sources on growth, photosynthetic activity, and secondary metabolism of common buckwheat. We hypothesized that LED light with the majority of red and blue waves would increase physiological and biochemical parameters compared to sunlight supplemented with HPS lamps. The experiment was performed in a phytotronic chamber (LEDs) and in a greenhouse (solar radiation supplemented with HPS lamps as a control). The effects were analyzed at the flowering phase with biometric measurements, leaf chlorophyll index, the kinetics of chlorophyll a fluorescence, content of soluble carbohydrates and phenolics in the leaves. Applied LED light decreased the biomass but stimulated the production of phenolics compared to control plants. In control plants, a positive correlation between flavonoid content and energy dissipation from photosystem II (DI_o/CS_m) was found, while in plants under LEDs total pool of phenolic content correlated with this parameter and the quantum yield of electron transport (φ Ro and ψ Ro) was lower than that of the control, probably affecting buckwheat biomass.

Genetic architecture of photosynthesis energy partitioning as revealed by a genome-wide association approach

The photosynthesis process is determined by the intensity level and spectral quality of the light; therefore, leaves need to adapt to a changing environment. The incident energy absorbed can exceed the sink capability of the photosystems, and, in this context, photoinhibition may occur in both photosystem II (PSII) and photosystem I (PSI). Quantum yield parameters analyses reveal how the energy is managed. These parameters are genotype-dependent, and this genotypic variability is a good opportunity to apply mapping association strategies to identify genomic regions associated with photosynthesis energy partitioning. An experimental and mathematical approach is proposed for the determination of an index which estimates the energy per photon flux for each spectral bandwidth (Δ_λ) of the light incident (QI index). Based on the QI, the spectral quality of the plant growth, environmental lighting, and the actinic light of PAM were quantitatively very similar which allowed an accurate phenotyping strategy of a rice population. A total of 143 genomic single regions associated with at least one trait of chlorophyll fluorescence were identified. Moreover, chromosome 5 gathers most of these regions indicating the importance of this chromosome in the genetic regulation of the photochemistry process. Through a GWAS strategy, 32 genes of rice genome associated with the main parameters of the photochemistry process of photosynthesis in rice were identified. Association between light-harvesting complexes and the potential quantum yield of PSII, as well as the relationship between coding regions for PSI-linked proteins in energy distribution during the photochemical process of photosynthesis is analyzed.

Acclimating Cucumber Plants to Blue Supplemental Light Promotes Growth in Full Sunlight

Raising young plants is important for modern greenhouse production. Upon transfer from the raising to the production environment, young plants should maximize light use efficiency while minimizing deleterious effects associated with exposure to high light (HL) intensity. The light spectrum may be used to establish desired traits, but how plants acclimated to a given spectrum respond to HL intensity exposure is less well explored. Cucumber (Cucumis sativus) seedlings were grown in a greenhouse in low-intensity sunlight (control; ∼2.7 mol photons m^-2 day^-1) and were treated with white, red, blue, or green supplemental light (4.3 mol photons m^-2 day^-1) for 10 days. Photosynthetic capacity was highest in leaves treated with blue light, followed by white, red, and green, and was positively correlated with leaf thickness, nitrogen, and chlorophyll concentration. Acclimation to different spectra did not affect the rate of photosynthetic induction, but leaves grown under blue light showed faster induction and relaxation of non-photochemical quenching (NPQ) under alternating HL and LL intensity. Blue-light-acclimated leaves showed reduced photoinhibition after HL intensity exposure, as indicated by a high maximum quantum yield of photosystem II photochemistry (F _v /F _m ). Although plants grown under different supplemental light spectra for 10 days had similar shoot biomass, blue-light-grown plants (B-grown plants) showed a more compact morphology with smaller leaf areas and shorter stems. However, after subsequent, week-long exposure to full sunlight (10.7 mol photons m^-2 day^-1), B-grown plants showed similar leaf area and 15% higher shoot biomass, compared to plants that had been acclimated to other spectra. The faster growth rate in blue-light-acclimated plants compared to other plants was mainly due to a higher photosynthetic capacity and highly regulated NPQ performance under intermittent high solar light. Acclimation to blue supplemental light can improve light use efficiency and diminish photoinhibition under high solar light exposure, which can benefit plant growth.

Accumulation of geranylgeranylated chlorophylls in the pigment-protein complexes of Arabidopsis thaliana acclimated to green light: effects on the organization of light-harvesting complex II and photosystem II functions

Light quality significantly influences plant metabolism, growth and development. Recently, we have demonstrated that leaves of barley and other plant species grown under monochromatic green light (500-590 nm) accumulated a large pool of chlorophyll a (Chl a) intermediates with incomplete hydrogenation of their phytyl chains. In this work, we studied accumulation of these geranylgeranylated Chls a and b in pigment-protein complexes (PPCs) of Arabidopsis plants acclimated to green light and their structural-functional consequences on the photosynthetic apparatus. We found that geranylgeranylated Chls are present in all major PPCs, although their presence was more pronounced in light-harvesting complex II (LHCII) and less prominent in supercomplexes of photosystem II (PSII). Accumulation of geranylgeranylated Chls hampered the formation of PSII and PSI super- and megacomplexes in the thylakoid membranes as well as their assembly into chiral macrodomains; it also lowered the temperature stability of the PPCs, especially that of LHCII trimers, which led to their monomerization and an anomaly in the photoprotective mechanism of non-photochemical quenching. Role of geranylgeranylated Chls in adverse effects on photosynthetic apparatus of plants acclimated to green light is discussed.

Light Quality-Dependent Regulation of Non-Photochemical Quenching in Tomato Plants

Simple Summary

Photosynthetic organisms, such as land plants, evolved to utilize available light and to use its energy to assimilate carbon dioxide and produce carbohydrates. However, the light intensity often exceeds the ability of plants to successfully utilize absorbed energy, thus inducing stress, manifested by an increased radical concentration inside plant cells and disruption of the inner structures, and consequently decreased plant yield. Plants solve this problem by using a mechanism termed non-photochemical quenching, by which they can dissipate the energy not used in photosynthesis. Modern agriculture, however, also involves indoor plant farming. For indoor plant farming LED-based lighting systems, with non-saturating light intensities, are suitable based on their restricted energy consumption. However, the composition of applied light should first be optimized to maximize its utilization. Our study examined the influence of monochromatic LEDs (red, green, and blue) on the photoprotective and photosynthetic properties of tomato plants. We indicate that monochromatic green light could be considered an important component of lighting systems to alleviate energy dissipation, while blue light enhances photosynthetic efficiency. Our study not only proves the crucial importance of spectrum optimization but also provides evidence that different light wavelengths modify photosynthetic and photoprotective properties.

Abstract

Photosynthetic pigments of plants capture light as a source of energy for photosynthesis. However, the amount of energy absorbed often exceeds its utilization, thus causing damage to the photosynthetic apparatus. Plants possess several mechanisms to minimize such risks, including non-photochemical quenching (NPQ), which allows them to dissipate excess excitation energy in the form of harmless heat. However, under non-stressful conditions in indoor farming, it would be favorable to restrict the NPQ activity and increase plant photosynthetic performance by optimizing the light spectrum. Towards this goal, we investigated the dynamics of NPQ, photosynthetic properties, and antioxidant activity in the leaves of tomato plants grown under different light qualities: monochromatic red (R), green (G), or blue (B) light (L) at 80 µmol m⁻² s⁻¹ and R:G:B = 1:1:1 (referred to as the white light (WL)) at 120 µmol m⁻² s⁻¹. The results confirm that monochromatic BL increased the quantum efficiency of PSII and photosynthetic pigments accumulation. The RL and BL treatments enhanced the NPQ amplitude and showed negative effects on antioxidant enzyme activity. In contrast, plants grown solely under GL or WL presented a lower amplitude of NPQ due to the reduced accumulation of NPQ-related proteins, photosystem II (PSII) subunit S (PsbS), PROTON GRADIENT REGULATION-LIKE1 (PGRL1), cytochrome b₆f subunit f (cytf) and violaxanthin de-epoxidase (VDE). Additionally, we noticed that plants grown under GL or RL presented an increased rate of lipid peroxidation. Overall, our results indicate the potential role of GL in lowering the NPQ amplitude, while the role of BL in the RGB spectrum is to ensure photosynthetic performance and photoprotective properties.

Effect of drought on photosynthesis, total antioxidant capacity, bioactive component accumulation, and the transcriptome of Atractylodes lancea

BACKGROUND

Atractylodes lancea (Thunb.) DC, a medicinal herb belonging to the Asteraceae family, often faces severe drought stress during its growth. Until now, there has been no research on the effect of drought stress on the quality formation of A. lancea. Therefore, the present study aimed to study the effects of drought stress on A. lancea through physical and chemical analysis, and to reveal the related molecular mechanisms via transcriptome analysis.

RESULTS

The photosynthesis was markedly inhibited under drought stress. There were alterations to photosynthetic parameters (Pn, Gs, Ci) and chlorophyll fluorescence (Fv/Fm, NPQ), and the chlorophyll content decreased. Twenty genes encoding important regulatory enzymes in light and dark reactions, including the Rubisco gene of the Calvin cycle, were significantly downregulated. After exposure to drought stress for more than 4 days, the activities of four antioxidative enzymes (SOD, POD CAT and APX) began to decrease and continued to decrease with longer stress exposure. Meanwhile, most of the genes encoding antioxidative enzymes were downregulated significantly. The downregulation of 21 genes related to the respiratory electron transport chain indicated that the blocked electron transfer accelerated excessive ROS. The MDA content was significantly elevated. The above data showed that 15 days of drought stress caused serious oxidative damage to A. lancea. Drought stress not only reduced the size and dry weight of A. lancea, but also lowered the amount of total volatile oil and the content of the main bioactive components. The total volatile oil and atractylodin content decreased slightly, whereas the content of atractylon and β-eudesmol decreased significantly. Moreover, ten significantly downregulated genes encoding sesquiterpene synthase were mainly expressed in rhizomes.

CONCLUSIONS

After exposed to drought stress, the process of assimilation was affected by the destruction of photosynthesis; stress tolerance was impaired because of the inhibition of the antioxidative enzyme system; and bioactive component biosynthesis was hindered by the downregulation of sesquiterpene synthase-related gene expression. All these had negative impacts on the quality formation of A. lancea under drought stress.

Photosynthetic apparatus performance of tomato seedlings grown under various combinations of LED illumination

It is already known that the process of photosynthesis depends on the quality and intensity of light. However, the influence of the new light sources recently used in horticulture, known as Light Emitting Diodes (LEDs), on this process is not yet fully understood. Chlorophyll a fluorescence measurement has been widely used as a rapid, reliable, and noninvasive tool to study the efficiency of the photosystem II (PSII) and to evaluate plant responses to various environmental factors, including light intensity and quality. In this work, we tested the responses of the tomato photosynthetic apparatus to different light spectral qualities. Our results showed that the best performance of the photosynthetic apparatus was observed under a mixture of red and blue light (R7:B3) or a mixture of red, green and blue light (R3:G2:B5). This was demonstrated by the increase in the effective photochemical quantum yield of PSII (Y[II]), photochemical quenching (qP) and electron transport rate (ETR). On the other hand, the mixture of red and blue light with a high proportion of blue light led to an increase in non-photochemical quenching (NPQ). Our results can be used to improve the production of tomato plants under artificial light conditions. However, since we found that the responses of the photosynthetic apparatus of tomato plants to a particular light regime were cultivar-dependent and there was a weak correlation between the growth and photosynthetic parameters tested in this work, special attention should be paid in future research.

Photobiological Effects on Biochemical Composition in Porphyridium cruentum (Rhodophyta) with a Biotechnological Application

This study describes the relation of photosynthetic capacity, growth and biochemical compounds in the microalgae Porphyridium cruentum under saturated irradiance (200 μmol m^-2  s^-1 ) by white light (WL) and low-pressure sodium vapor lamps (SOX lamps-control) and supplemented by fluorescent lamps (FLs) with different light qualities (blue: λ_max = 440 nm; green: λ_max = 560 nm; and red: λ_max = 660 nm). The maximum photosynthetic efficiency (F_v / F_m ) showed a positive correlation with the light quality by saturating light SOX in mixture with stimulating blue light than the white light (WL) at the harvest day (10 days). The production, that is maximal electron transport rate (ETR_max ), and energy dissipation, that is maximal nonphotochemical quenching (NPQ_max ), had the same pattern throughout the time (3-6 days) being the values higher under white light (WL) compared with SOX and SOX plus supplemented different light qualities. Total protein levels increased significantly in the presence of SOX light, while phycoerythrin (B-PE) showed significant differences under SOX+ blue light. Arachidonic acid (ARA) was higher under SOX and SOX plus supplemented different light qualities than that under WL, whereas eicosapentaenoic acid (EPA) was the reverse. The high photomorphogenic potential by SOX light shows promising application for microalgal biotechnology.

Recent advances in understanding and improving photosynthesis

Since 1893, when the word "photosynthesis" was first coined by Charles Reid Barnes and Conway MacMillan, our understanding of the elements and regulation of this complex process is far from being entirely understood. We aim to review the most relevant advances in photosynthesis research from the last few years and to provide a perspective on the forthcoming research in this field. Recent discoveries related to light sensing, harvesting, and dissipation; kinetics of CO₂ fixation; components and regulators of CO₂ diffusion through stomata and mesophyll; and genetic engineering for improving photosynthetic and production capacities of crops are addressed.

Improved photosystem II and defense enzymes activity in rice (Oryza sativa) by biopriming against Xanthomonas oryzae pv. oryzae

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat to rice production as it accounts for loss up to 50% of annual rice grain yield. Xoo causes leaf tissue necrosis and as a result there is downregulation of the photosynthetic mechanisms of plant. Measurement of chl a fluorescence is an easy, fast, non-invasive and highly sensitive technique that can be used to understand plant health by measuring alterations in PSII activity, in response to different biotic and abiotic stresses. In the present investigation, rice seeds were bio-primed with two bacterial spp. (e.g. Bacillus subtilis and B. megaterium) and one fungal strain (i.e. Trichoderma erinaceum). The induction of defence against BB disease by bio-priming with biotic agents, was studied as response in alteration of PSII and defence enzymes activity. Field experiment was conducted with the best biotic agent; i.e. B. subtilis obtained from all experiments to study whether defence induction by it have any side effect on rice yield and biomass. Net house and field experiments have suggested that among all the biotic agents studied, bio-priming of rice seeds with B. subtilis has protected the photosynthetic machinery of plants from being damaged by BB without having any detrimental effect on rice grain yield.

Effect of red light on photosynthetic acclimation and the gene expression of certain light signalling components involved in the microRNA biogenesis in the extremophile Eutrema salsugineum

The photosynthetic acclimation of extremophile Eutrema salsugineum plants to red light (RL) (14 days, 150 μmol photons m^-2 s^-1, 660 nm) and the expression of the key photoreceptor apoprotein genes, transcription factors (TFs) and associated with phytochrome system MIR (microRNA) genes were studied. RL exposure induced an increase in the content of anthocyanin and total phenolic compounds and the level of Chls was decreased. The photosystem 2 electron transport rate and the number of open reaction centres (q_L) were not changed in RL plants, however, the levels of non-photochemical quenching (NPQ) and the regulated quantum yield of non-photochemical quenching Y(NPQ) were significantly higher in the RL plants. The rate of CO₂ uptake was decreased by almost 1.4-fold but the respiration and transpiration rates, as well as the stomatal conductance were not changed in the RL plants. An increase in the expression of the photoreceptor apoprotein genes PHYA, PHYB and PHYC, the TF genes PIF4, PIF5 and miR395, miR408, miR165 and decreases in the levels of the transcripts of the TF gene HY5 and miR171, miR157, and miR827 were detected. The acclimation effect of photosynthetic apparatus to RL was accompanied by an increase of pigment content such as total phenolic compounds and carotenoids and it is due to the changes in the expression of the apoprotein phytochrome genes PHYA, PHYB, PHYC and phytochrome signalling TFs (PIF4, PIF5 and HY5) as well as MIR genes associated with phytochrome system.

Plasticity of photosynthetic processes and the accumulation of secondary metabolites in plants in response to monochromatic light environments: A review

Light spectra significantly influence plant metabolism, growth and development. Here, we review the effects of monochromatic blue, red and green light compared to those of multispectral light sources on the morpho-anatomical, photosynthetic and molecular traits of herbaceous plants. Emphasis is given to the effect of light spectra on the accumulation of secondary metabolites, which are important bioactive phytochemicals that determine the nutritional quality of vegetables. Overall, blue light may promote the accumulation of phenylpropanoid-based compounds without substantially affecting plant morpho-anatomical traits compared to the effects of white light. Red light, conversely, strongly alters plant morphology and physiology compared to that under white light without showing a consistent positive effect on secondary metabolism. Due to species-specific effects and the small shifts in the spectral band within the same color that can substantially affect plant growth and metabolism, it is conceivable that monochromatic light significantly affects not only plant photosynthetic performance but also the "quality" of plants by modulating the biosynthesis of photoprotective compounds.

CO2 uptake and chlorophyll a fluorescence of Suaeda fruticosa grown under diurnal rhythm and after transfer to continuous dark

Although only 2-4% of absorbed light is emitted as chlorophyll (Chl) a fluorescence, its measurement provides valuable information on photosynthesis of the plant, particularly of Photosystem II (PSII) and Photosystem I (PSI). In this paper, we have examined photosynthetic parameters of Suaeda fruticosa L. (family: Amaranthaceae), surviving under extreme xerohalophytic conditions, as influenced by diurnal rhythm or continuous dark condition. We report here CO₂ gas exchange and the kinetics of Chl a fluorescence of S. fruticosa, made every 3 hours (hrs) for 3 days, using a portable infra-red gas analyzer and a Handy PEA fluorimeter. Our measurements on CO₂ gas exchange show the maximum rate of photosynthesis to be at 08:00 hrs under diurnal condition and at 05:00 hrs under continuous dark. From the OJIP phase of Chl a fluorescence transient, we have inferred that the maximum quantum yield of PSII photochemistry must have increased during the night under diurnal rhythm, and between 11:00 and 17:00 hrs under constant dark. Overall, our study has revealed novel insights into how photosynthetic reactions are affected by the photoperiodic cycles in S. fruticosa under high salinity. This study has further revealed a unique strategy operating in this xero-halophyte where the repair mechanism for damaged PSII operates during the dark, which, we suggest, contributes to its ecological adaptation and ability to survive and reproduce under extreme saline, high light, and drought conditions. We expect these investigations to help in identifying key genes and pathways for raising crops for saline and dry areas.

A sixty-year tryst with photosynthesis and related processes: an informal personal perspective

After briefly describing my early collaborative work at the University of Allahabad, that had laid the foundation of my research life, I present here some of our research on photosynthesis at the University of Illinois at Urbana-Champaign, randomly selected from light absorption to NADP⁺ reduction in plants, algae, and cyanobacteria. These include the fact that (i) both the light reactions I and II are powered by light absorbed by chlorophyll (Chl) a of different spectral forms; (ii) light emission (fluorescence, delayed fluorescence, and thermoluminescence) by plants, algae, and cyanobacteria provides detailed information on these reactions and beyond; (iii) primary photochemistry in both the photosystems I (PS I) and II (PS II) occurs within a few picoseconds; and (iv) most importantly, bicarbonate plays a unique role on the electron acceptor side of PS II, specifically at the two-electron gate of PS II. Currently, the ongoing research around the world is, and should be, directed towards making photosynthesis better able to deal with the global issues (such as increasing population, dwindling resources, and rising temperature) particularly through genetic modification. However, basic research is necessary to continue to provide us with an understanding of the molecular mechanism of the process and to guide us in reaching our goals of increasing food production and other chemicals we need for our lives.

A New Light on Photosystem II Maintenance in Oxygenic Photosynthesis

Life on earth is sustained by oxygenic photosynthesis, a process that converts solar energy, carbon dioxide, and water into chemical energy and biomass. Sunlight is essential for growth and productivity of photosynthetic organisms. However, exposure to an excessive amount of light adversely affects fitness due to photooxidative damage to the photosynthetic machinery, primarily to the reaction center of the oxygen-evolving photosystem II (PSII). Photosynthetic organisms have evolved diverse photoprotective and adaptive strategies to avoid, alleviate, and repair PSII damage caused by high-irradiance or fluctuating light. Rapid and harmless dissipation of excess absorbed light within antenna as heat, which is measured by chlorophyll fluorescence as non-photochemical quenching (NPQ), constitutes one of the most efficient protective strategies. In parallel, an elaborate repair system represents another efficient strategy to maintain PSII reaction centers in active states. This article reviews both the reaction center-based strategy for robust repair of photodamaged PSII and the antenna-based strategy for swift control of PSII light-harvesting (NPQ). We discuss evolutionarily and mechanistically diverse strategies used by photosynthetic organisms to maintain PSII function for growth and productivity under static high-irradiance light or fluctuating light environments. Knowledge of mechanisms underlying PSII maintenance would facilitate bioengineering photosynthesis to enhance agricultural productivity and sustainability to feed a growing world population amidst climate change.