Efficiency Of Photosynthetic Electron Transport Research Articles

Tree diversity affects chlorophyll a fluorescence and other leaf traits of tree species in a boreal forest.

An assemblage of tree species with different crown properties creates heterogeneous environments at the canopy level. Changes of functional leaf traits are expected, especially those related to light interception and photosynthesis. Chlorophyll a fluorescence (ChlF) properties in dark-adapted leaves, specific leaf area, leaf nitrogen content (N) and carbon isotope composition (δ13C) were measured on Picea abies (L.) H.Karst., Pinus sylvestris L. and Betula pendula Roth. in monospecific and mixed boreal forests in Europe, in order to test whether they were affected by stand species richness and composition. Photosynthetic efficiency, assessed by induced emission of leaf ChlF, was positively influenced in B. pendula by species richness, whereas P. abies showed higher photosynthetic efficiency in monospecific stands. Pinus sylvestris had different responses when it coexisted with P. abies or B. pendula. The presence of B. pendula, but not of P. abies, in the forest had a positive effect on the efficiency of photosynthetic electron transport and N in P. sylvestris needles, and the photosynthetic responses were positively correlated with an increase of leaf δ13C. These effects on P. sylvestris may be related to high light availability at the canopy level due to the less dense canopy of B. pendula. The different light requirements of coexisting species was the most important factor affecting the distribution of foliage in the canopy, driving the physiological responses of the mixed species. Future research directions claim to enhance the informative potential of the methods to analyse the responses of pure and mixed forests to environmental factors, including a broader set of plant species' functional traits and physiological responses.

Salt response of photosynthetic electron transport system in wheat cultivars with contrasting tolerance

Soil salinity significantly decreases the photosynthetic efficiency and plant growth in wheat (Triticum aestivum L.). However, sensitivity of the photosynthetic electron transport system of wheat in relation with salt stress is unclear. Two wheat cultivars with contrasting salt tolerance were exposed to soil salinity, and the physiological responses and performance of photosynthetic electron system were investigated. The depressed photosynthetic carbon assimilation was mainly caused by stomatal closure and lower photosynthetic electron transport efficiency. Under salt stress, the salt-resistant cv. YN19 had higher efficiency in photosynthetic electron transport, hence maintaining higher photosynthetic rate under salt stress, compared with the salt-sensitive cv. JM22. In addition, the parameters derived from fast chlorophyll a fluorescence induction curve, i.e. the quantum yield for electron transport (φEo) and the probability that an electron moves futher than QA (ψEo), can be used as indicators for rapid screening of wheat cultivars tolerant to soil salinity.

Toxic effects of 1,4-dichlorobenzene on photosynthesis in Chlorella pyrenoidosa

1,4-Dichlorobenzene (1,4-DCB) is a common organic contaminant in water. To determine the effects of this contaminant on photosynthesis in the freshwater alga Chlorella pyrenoidosa, algal cells were treated with 1,4-DCB at different concentrations for various times, and their photosynthetic pigment contents and chlorophyll fluorescence traits were analyzed. The results showed that 1,4-DCB exerted toxic effects on photosynthesis in C. pyrenoidosa, especially at concentrations exceeding 10mg/L. The inhibitory effects of 1,4-DCB were time- and concentration-dependent. After treatment with 1,4-DCB (≥10mg/L), the contents of photosynthetic pigments decreased significantly, the photosystem II reaction center was irreversibly damaged, and the quantum yield of photosystem II decreased significantly. Also, there were sharp decreases in the efficiency of photosynthetic electron transport and energy conversion. Photosystem II became overloaded as the amount of excitation energy distributed to it increased. All of these events weakened the photochemical reaction, and ultimately led to serious inhibition of photosynthesis.

Hybrid sorrel (Rumex tianschanicus × Rumex patientia) a high biomass yielding plant as an interesting object of physiological research

Hybrid sorrel (Rumex tianschanicus × Rumex patientia) a high biomass yielding plant as an interesting object of physiological research

花生叶片蛋白组对UV-B辐射增强的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 花生叶片蛋白组对UV-B辐射增强的响应 DOI: 10.5846/stxb201302030223 作者: 作者单位: 三峡库区生态环境教育部重点实验室,台州学院生态研究所,三峡库区生态环境教育部重点实验室,中国科学院植物研究所植被与环境变化国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（30670334，31270461）；浙江省教育厅科研项目（Y201223322）；中央高校基本科研业务费专项资金资助项目（XDJK2011D009） A proteomic analysis of Arachis hypogaea leaf in responses to enhanced ultraviolet-B radiation Author: Affiliation: MOE Key Laboratory of Eco-environments of Three Gorges Reservoir Region,School of Life Science,Southwest University,Institute of Ecology,Taizhou University,MOE Key Laboratory of Eco-environments of Three Gorges Reservoir Region,School of Life Science,Southwest University,State Key Laboratory of Vegetation and Environmental Change,Institute of Botany,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为揭示UV-B辐射增强处理降低花生光合速率和花生抵御UV-B辐射增强的分子机制，应用蛋白质双向电泳与质谱联用技术对自然光环境下补增UV-B辐射（54 μW/cm2）处理24h的苗期花生叶片差异表达蛋白质变化进行了分析。结果表明：补增UV-B处理下，花生叶片中共检测到丰度变化在2.5倍以上的差异表达蛋白点39个（其中22种蛋白质表达下调，17种表达上调），经过MALDI-TOF-TOF分析及数据库检索，成功鉴定出其中的27种蛋白质。被鉴定的27种蛋白质按其功能大致可归为8类，第Ⅰ类：光合作用相关的蛋白质，包括质体蓝素、1，5-二磷酸核酮糖羧化酶小亚基、放氧复合物增强子蛋白1、PsbP结构域蛋白6和果糖二磷酸醛缩酶；第Ⅱ类：糖代谢相关蛋白质，包括苹果酸脱氢酶；第Ⅲ类：能量合成相关蛋白质，包括ATP合酶；第Ⅳ类：氨基酸代谢相关蛋白质，包括半胱氨酸合成酶；第Ⅴ类：蛋白质加工相关蛋白质，包括热激蛋白；第Ⅵ类：蛋白质翻译相关蛋白质，包括核糖体循环因子；第Ⅶ类：防御相关蛋白质，包括几丁质酶、过氧化物酶、Cu-Zn超氧化物歧化酶、二羟肉桂酸3-O-转甲基酶和类萌发素蛋白；第Ⅷ类，未知功能蛋白质。这些研究结果为进一步研究花生抵御UV-B辐射的分子机理提供了有意义的线索。 Abstract:Ultraviolet-B (UV-B, 280-320 nm) constitutes a minor part of the solar spectrum, which can be absorbed by stratospheric ozone layer. However, a global depletion of the ozone layer, largely due to the release of man-made chlorofluorocarbons, has resulted in an increase of ground-level solar UV-B radiation. UV-B can influence plant processes, either through direct damage or via various regulatory effects. Many researches have warned that excessive UV-B radiation can harm living organisms by damaging DNA, proteins, lipids, and membranes and consequently affecting plant growth, development, morphology, and productivity. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is a powerful technique for resolving hundreds of proteins in parallel. Combined with mass spectrometry (MS), it allows rapid and reliable protein identification. In recent years, proteomic-based technologies have been successfully applied to systematic studies of the stress responses many plant species, including Arabidopsis, soybean, rice, wheat, barley, potato, tomato, and many others. A wide range of abiotic stresses have been examined, such as drought, nutrition deficiency, temperature, oxidative stress, herbicides, wounding, anoxia, salt, and heavy metals. These investigations have provided a wealth of important information on the physiological processes involved in plant stress responses. To explore the molecular mechanisms of the decreased photosynthetic rate and the resistance of peanut (Arachis hypogaea) when exposed to enhanced UV-B radiation, 2-D PAGE and MS were used to identify the differentially-expressed proteins in peanut seedling leaves in response to supplementary UV-B radiation (54 μW/cm2) for 24 h. A total of 39 protein spots were differentially expressed by at least 2.5 fold compared with the controls (22 proteins were down-regulated and 17 were up-regulated) after treatment with supplementary UV-B radiation. Of those protein spots, 27 were successfully identified by MALDI TOF/TOF MS after a database search. Those 27 proteins could be classified into eight categories according to their functions: class Ⅰ, photosynthesis (plastocyanin, ribulose-1,5-bisphosphate carboxylase small subunit, oxygen-evolving enhancer protein 1, PsbP domain-containing protein 6, and fructose-bisphosphate aldolase); class Ⅱ, carbohydrate metabolism (malate dehydrogenase); class Ⅲ, energy synthesis (ATP synthase); class Ⅳ, amino acid biosynthesis (cysteine synthase); class Ⅴ, protein biosynthesis (ribosome recycling factor); class Ⅵ, protein processing (heat shock proteins); class Ⅶ, defense responses (chitinase, peroxidase, Cu-Zn SOD, caffeic acid 3-O-methyltransferase, and germin-like protein); class Ⅷ, unknown proteins. In conclusion, we hypothesized that the enhanced UV-B radiation caused a decrease in the photosynthesis rate of peanut leaves mainly via three mechanisms. First, enhanced UV-B may down-regulate the expression of ribosome recycling factor, which caused a decrease in the expression of subunit PsbP in photosystem Ⅱ, thus destroying the thylakoid membrane structure. Second, the reduced plastocyanin expression may have induced a decrease in photosynthetic electron transport efficiency. Third, the down-regulation of ribulose-1,5-bisphosphate carboxylase and fructose-1,6-bisphosphate aldolase resulted in a decrease in carbon assimilation. At the same time, peanut may also enhance its resistance to UV-B stress by increasing the expressions of antioxidant enzymes and non-enzymatic antioxidants, germin-like proteins, pathogenesis-related proteins, and heat shock proteins. These results provide important information for understanding the molecular mechanisms by which A. hypogaea responds to elevated UV-B stress. 参考文献 相似文献 引证文献

Spatiotemporal Analysis of Copper Homeostasis in Populus trichocarpa Reveals an Integrated Molecular Remodeling for a Preferential Allocation of Copper to Plastocyanin in the Chloroplasts of Developing Leaves

Plastocyanin, which requires copper (Cu) as a cofactor, is an electron carrier in the thylakoid lumen and essential for photoautotrophic growth of plants. The Cu microRNAs, which are expressed during Cu deprivation, down-regulate several transcripts that encode for Cu proteins. Since plastocyanin is not targeted by the Cu microRNAs, a cofactor economy model has been proposed in which plants prioritize Cu for use in photosynthetic electron transport. However, defects in photosynthesis are classic symptoms of Cu deprivation, and priorities in Cu cofactor delivery have not been determined experimentally. Using hydroponically grown Populus trichocarpa (clone Nisqually-1), we have established a physiological and molecular baseline for the response to Cu deficiency. An integrated analysis showed that Cu depletion strongly reduces the activity of several Cu proteins including plastocyanin, and consequently, photosynthesis and growth are decreased. Whereas plastocyanin mRNA levels were only mildly affected by Cu depletion, this treatment strongly affected the expression of other Cu proteins via Cu microRNA-mediated transcript down-regulation. Polyphenol oxidase was newly identified as Cu regulated and targeted by a novel Cu microRNA, miR1444. Importantly, a spatiotemporal analysis after Cu resupply to previously depleted plants revealed that this micronutrient is preferentially allocated to developing photosynthetic tissues. Plastocyanin and photosynthetic electron transport efficiency were the first to recover after Cu addition, whereas recovery of the other Cu-dependent activities was delayed. Our findings lend new support to the hypothesis that the Cu microRNAs serve to mediate a prioritization of Cu cofactor use. These studies also highlight poplar as an alternative sequenced model for spatiotemporal analyses of nutritional homeostasis.

Comparative phosphoproteome profiling reveals a function of the STN8 kinase in fine-tuning of cyclic electron flow (CEF)

Important aspects of photosynthetic electron transport efficiency in chloroplasts are controlled by protein phosphorylation. Two thylakoid-associated kinases, STN7 and STN8, have distinct roles in short- and long-term photosynthetic acclimation to changes in light quality and quantity. Although some substrates of STN7 and STN8 are known, the complexity of this regulatory kinase system implies that currently unknown substrates connect photosynthetic performance with the regulation of metabolic and regulatory functions. We performed an unbiased phosphoproteome-wide screen with Arabidopsis WT and stn8 mutant plants to identify unique STN8 targets. The phosphorylation status of STN7 was not affected in stn8, indicating that kinases other than STN8 phosphorylate STN7 under standard growth conditions. Among several putative STN8 substrates, PGRL1-A is of particular importance because of its possible role in the modulation of cyclic electron transfer. The STN8 phosphorylation site on PGRL1-A is absent in both monocotyledonous plants and algae. In dicots, spectroscopic measurements with Arabidopsis WT, stn7, stn8, and stn7/stn8 double-mutant plants indicate a STN8-mediated slowing down of the transition from cyclic to linear electron flow at the onset of illumination. This finding suggests a possible link between protein phosphorylation by STN8 and fine-tuning of cyclic electron flow during this critical step of photosynthesis, when the carbon assimilation is not commensurate to the electron flow capacity of the chloroplast.

Revegetation of a Uranium Mine Dump by Using Fertilizer Treated Sessile Oaks

The rehabilitation of contaminated sites and the establishment of suitable trees for revegetation purposes is often problematic due to the mostly suboptimal nutrient supply and the poor humus reservoir. For these reasons hydrogels (Stockosorb®) and novel humus substitutes (NOVIHUM®), serving as long lasting fertilizer (LLF), were recently tested successfully. At the beginning of this multiyear study, those LLFs were administered to the root zone of young sessile oaks (Quercus petraea (Mattuschka) Liebl.), growing in test trials on a uranium mine dump in Schlema (Germany). To quantify the effect of LLFs on plant vitality, chlorophyll a fluorescence measurements and JIP test analyses were used. The results revealed up to 49% higher average photosynthetic vitality (PIABS) of the LLF treated plants compared to controls. Particularly in the first test year, the efficiency of photosynthetic electron transport was strongly increased. This stimulation of photosynthetic activity was supported by direct measurements showing up to 129% increased diameter growth of the treated plants after a four year experimental period.Furthermore an increase of the maximum water holding capacity of the dump soil was attained by using LLFs. Overall, the findings reported here represent a feasible, ecologically justifiable reforestation method with a low environmental hazard potential.

The effects of brassinosteroids on photosynthetic parameters in leaves of two field-grown maize inbred lines and their F1 hybrid

The effect of foliar spray with 10-12 M aqueous solutions of 24-epibrassinolide or a synthetic androstane analogue of castasterone on the activity of photosystem (PS) 1, the Hill reaction activity, the content of photosynthetic pigments and the specific leaf mass was examined for three different leaves developed after brassinosteroid (BR) treatment in two inbred lines of field-grown maize and their F1 hybrid. The brassinosteroids significantly affected neither the efficiency of photosynthetic electron transport, nor the content of chlorophylls or carotenoids.

Arabidopsis thaliana PGR7 encodes a conserved chloroplast protein that is necessary for efficient photosynthetic electron transport.

A significant fraction of a plant's nuclear genome encodes chloroplast-targeted proteins, many of which are devoted to the assembly and function of the photosynthetic apparatus. Using digital video imaging of chlorophyll fluorescence, we isolated proton gradient regulation 7 (pgr7) as an Arabidopsis thaliana mutant with low nonphotochemical quenching of chlorophyll fluorescence (NPQ). In pgr7, the xanthophyll cycle and the PSBS gene product, previously identified NPQ factors, were still functional, but the efficiency of photosynthetic electron transport was lower than in the wild type. The pgr7 mutant was also smaller in size and had lower chlorophyll content than the wild type in optimal growth conditions. Positional cloning located the pgr7 mutation in the At3g21200 (PGR7) gene, which was predicted to encode a chloroplast protein of unknown function. Chloroplast targeting of PGR7 was confirmed by transient expression of a GFP fusion protein and by stable expression and subcellular localization of an epitope-tagged version of PGR7. Bioinformatic analyses revealed that the PGR7 protein has two domains that are conserved in plants, algae, and bacteria, and the N-terminal domain is predicted to bind a cofactor such as FMN. Thus, we identified PGR7 as a novel, conserved nuclear gene that is necessary for efficient photosynthetic electron transport in chloroplasts of Arabidopsis.

Chloroplast NAD Kinase is Essential for Energy Transduction Through the Xanthophyll Cycle in Photosynthesis

Photosynthetic parameters of the nadk2 mutant of Arabidopsis thaliana, which is defective in chloroplast NAD kinase, were investigated. In this plant, the effective efficiency of photosynthetic electron transport (PhiII) and the quantum yield of open reaction centers of photosystem II (Fv'/Fm') were decreased. Furthermore, an increase in non-photochemical quenching attributed to energy dissipation from the xanthophyll cycle was observed. The mutant showed an aberrant de-epoxidation state of xanthophyll cycle carotenoids and had a high level of zeaxanthin even under low light conditions. These results indicate that chloroplast NAD kinase, catalyzing phosphorylation of NAD, is essential for the proper photosynthetic machinery of PSII and the xanthophyll cycle.

Photosynthesis and photoinhibition in a tropical alpine giant rosette plant, Lobelia rhynchopetalum.

Carbodioxide uptake, oxygen evolution and chlorophyll fluorescence of leaves of Lobelia Lobelia rhynchopetalum Hemsl., a giant rosette plant of the tropical alpine regions of Ethiopia, were studied under field conditions at 4000 m above sea level. Our objective was to investigate the photosynthetic adaptation to the combination of wide fluctuation in diurnal temperature, high photon flux densities (PFD) and low CO2 partial pressure encountered in these regions. At an ambient CO2 partial pressure of c. 17 Pa, maximal rates of CO2 uptake were low, ranging between 4 and 6 μmol m-2 s-1 . Such rates, however, required high PFDs and were observed only at levels of 1500 μmol photons m-2 s-2 . Carbon dioxide uptake was significantly inhibited when PFD was ≤ 2000 μmol photons m-2 s-1 . On the other hand, at saturating CO2 levels, maximal photosynthetic oxygen evolution was higher (30 μmol C2 m-2 s-1 ). saturating at the same PFD as CO2 uptake. Quantum efficiency of CO2 uptake (0.006 mol CO2 mol photons-1 , at high altitude and a low CO, partial pressure of 17 Pa) and even of oxygen evolution under CO2 -saturating conditions in the leaf O2 electrode (0.05 mol O2 mo) photons-1 ) indicated reduced photosynthetic efficiency. Electron transport rate (ETR) was strongly correlated with the leaf temperature. Non-photochemical quenching (NPQ) responded inversely to leaf temperature and stomatal conductance. The results indicated that in the morning, when the sun irradiates the partly frozen leaves with closed stomata, NPQ is the principal mechanism by which Lobelia leaves protect their photosynthetic apparatus. However, during the day, the predominant upright inclination of the leaves significantly contributes to protecting the leaves from excess light absorption. A comparison of the chlorophyll fluorescence of young and old leaves revealed that the former had high ETR and quantum efficiency of photosynthetic electron transport but a lower capacity for NPQ. Extremely high NPQ values but low ETR and low quantum efficiency were recorded for the old leaves. Thus, in the course of maturation the leaves apparently lose photosynthetic efficiency but increase their capability for protective non-photochemical quenching.

Photosynthetic CO 2-Assimilation, Chlorophyll Fluorescence and Zeaxanthin Accumulation in Field Grown Maple Trees in the Course of a Sunny and a Cloudy Day

Changes in photosynthetic CO 2 fixation, variable chlorophyll fluorescence ratios, carotenoid composition, zeaxanthin accumulation and the de-epoxidation state DEPS of the zeaxanthin cycle were simultaneously determined in leaves of field-grown maple trees (Acer platanoides L.) on a sunny and a cloudy day in August. In the course of the sunny day the photosynthetic net CO 2 assimilation rates P N rose with the PPFD in the morning and were then predominantly determined by the stomata opening (partial closure at noon and further closure in the afternoon as seen from the decrease in gH 2 O-values). When the rate of Co 2 -fixation began to decrease at a high sun irradiance (high PPFD) at about 10 :00 am (partial closure of stomata), large zeaxanthin amounts were accumulated in a biphasic process : 1) by a fast phototransformation of existing violaxanthin into zeaxanthin and 2) by a slow but continuous increase of the zeaxanthin level of 50 to 60% via de novo biosynthesis. A strong zeaxanthin accumulation depends on a high proton gradient and only proceeded when P N was light-saturated and was reduced by a partial closure of stomata. The zeaxanthin accumulation in the morning followed the rise in PPFD with some delay as well as the zeaxanthin retransformation to violaxanthin at the PPFD decrease in the late afternoon and evening. On the sunny day the photochemical and non-photochemical quenching coefficients of the chlorophyll fluorescence, qP and qN, showed an inverse relationship. With increasing PPFD qP declined to very low values (below 0.1) and qN increased to high values >0.9. The variable chlorophyll fluorescence ratios Fv'/Fm' and ΔF/Fm', indicators of the quantum efficiency of photosynthetic electron transport of photosystem II, declined parallel to the high PPFD-induced decline of qP and the rise in qN. There was, however, no clear correlation between the changes in chlorophyll fluorescence parameters and the rise and fall of zeaxanthin in the course of the sunny day. In fact, in the afternoon the zeaxanthin level decreased much earlier than the decline in qN and the rise and regeneration of the initial values of qP, Fv'/Fm' or ΔF/Fm'. Despite the strong increase in qN and the large decrease in qP, Fv'/Fm' and ΔF/Fm', the net CO 2 assimilation rates P N of maple leaves only declined by 22 % as compared to the maximum P N values at 10 :15 am indicating that the photosynthetic apparatus was only marginally photoinhibited. It is assumed that only a small fraction of chloroplasts at the upper leaf side became photoinhibited and functioned as a light filter for the other chloroplasts in the lower mesophyll parts which remained photosynthetically active. The results demonstrate that the changes of the chlorophyll fluorescence parameters qP and qN as well as of the ratios Fv'/Fm' or ΔF/Fm', measured with the PAM fluorometer at the upper leaf side, are not representative of the total pool of leaf chloroplasts. For this reason it is suggested to measure the chlorophyll fluorescence parameters not only at the upper but also at the lower leaf side in order to obtain more representative information on the chloroplasts of the whole leaf. In addition, chlorophyll fluorescence measurements should always be complemented by net CO 2 fixation measurements in order to investigate to which degree a presumed photoinhibition really exists at the whole leaf level. On the cloudy day up to 3 pm the PPFD was very low, yet net photosynthesis (P N ) was performed at good rates.

Photosynthetic electron transport in tobacco leaves infected with tobacco mosaic virus

Tobacco (Nicotiana tabacum L. cv. Samsun) plants inoculated with different strains of tobacco mosaic virus (TMV) inducing mosaic symptoms of widely varying severity were studied with in vivo chlorophyll fluorescence. This method was used to deduce photosynthetic electron transport efficiency in relation to symptom expression. The quantum yields of photosystem II (PS II) electron transport rate were significantly diminished in virus strains inducing loss of chlorophyll. The reduction in young mosaic‐diseased leaves appeared to be due in part to a reduction in the fraction of open reaction centers, whereas in older leaves exhibiting less pronounced symptoms the reduction was mainly caused by a reduced efficiency of capture of excitation energy of open PS II reaction centers. Upon infection with any of the five virus strains PS II seemed to be irreversibly damaged in the inoculated leaves and the ones directly above, indicative of a possible increased susceptibility to photoinhibition in these leaves (Somersalo and Krause 1989) even when no symptoms were apparent. Symptom expression did not appear to be related to the influence of the virus on PS II activity, because the severest effects occurred in the inoculated leaves, which either remained symptomless or developed slight yellowing only. This study demonstrates the usefulness or modulated chlorophyll fluorescence measurements for the investigation of plant‐virus interactions. It is particularly important when visual symptoms are absent.

Adjustments of photosystem stoichiometry in chloroplasts improve the quantum efficiency of photosynthesis.

The efficiency of photosynthetic electron transport depends on the coordinated interaction of photosystem II (PSII) and photosystem I (PSI) in the electron-transport chain. Each photosystem contains distinct pigment-protein complexes that harvest light from different regions of the visible spectrum. The light energy is utilized in an endergonic electron-transport reaction at each photosystem. Recent evidence has shown a large variability in the PSII/PSI stoichiometry in plants grown under different environmental irradiance conditions. Results in this work are consistent with the notion of a dynamic, rather than static, thylakoid membrane in which the stoichiometry of the two photosystems is adjusted and optimized in response to different light quality conditions. Direct evidence is provided that photosystem stoichiometry adjustments in chloroplasts are a compensation strategy designed to correct unbalanced absorption of light by the two photosystems. Such adjustments allow the plant to maintain a high quantum efficiency of photosynthesis under diverse light quality conditions and constitute acclimation that confers to plants a significant evolutionary advantage over that of a fixed photosystem stoichiometry in thylakoid membranes.