Efficiency Of Photosynthetic Electron Transport Research Articles

Toxicity of the sunscreen UV filter benzophenone-3 (OBZ) to the microalga Selenastrum capricornutum: An insight into OBZ’s damage to photosynthesis and respiration

Oxybenzone (OBZ; benzophenone-3, CAS# 131–57–7), as a new pollutant and ultraviolet absorbent, shows a significant threat to the survival of phytoplankton. This study aims to explore the acute toxic effects of OBZ on the growth of the microalga Selenastrum capricornutum, as well as the mechanisms for its damage to the primary metabolic pathways of photosynthesis and respiration. The results demonstrated that the concentrations for 50 % of maximal effect (EC50) of OBZ for S. capricornutum were 9.07 mg L−1 and 8.54 mg L−1 at 72 h and 96 h, respectively. A dosage of 4.56 mg L−1 OBZ significantly lowered the photosynthetic oxygen evolution rate of S. capricornutum in both light and dark conditions for a duration of 2 h, while it had no effect on the respiratory oxygen consumption rate under darkness. OBZ caused a significant decline in the efficiency of photosynthetic electron transport due to its damage to photosystem II (PSII), thereby decreasing the photosynthetic oxygen evolution rate. Over-accumulated H2O2 was produced under light due to the damage caused by OBZ to the donor and acceptor sides of PSII, resulting in increased peroxidation of cytomembranes and inhibition of algal respiration. OBZ’s damage to photosynthesis and respiration will hinder the conversion and reuse of energy in algal cells, which is an important reason that OBZ has toxic effects on S. capricornutum. The present study indicated that OBZ has an acute toxic effect on the microalga S. capricornutum. In the two most important primary metabolic pathways in algae, photosynthesis is more sensitive to the toxicity of OBZ than respiration, especially in the dark.

Divergent protein redox dynamics and their relationship with electron transport efficiency during photosynthesis induction.

Various chloroplast proteins are activated/deactivated during the light/dark cycle via the redox regulation system. Although the photosynthetic electron transport chain provides reducing power to redox-sensitive proteins via the ferredoxin (Fd)/thioredoxin (Trx) pathway for their enzymatic activity control, how the redox states of individual proteins are linked to electron transport efficiency remains uncharacterized. Here we addressed this subject with a focus on the photosynthetic induction phase. We used Arabidopsis plants, in which the amount of Fd-Trx reductase (FTR), a core component in the Fd/Trx pathway, was genetically altered. Several chloroplast proteins showed different redox shift responses toward low- and high-light treatments. The light-dependent reduction of Calvin-Benson cycle enzymes fructose 1,6-bisphosphatase (FBPase) and sedoheptulose 1,7-bisphosphatase (SBPase) was partially impaired in the FTR-knockdown ftrb mutant. Simultaneous analyses of chlorophyll fluorescence and P700 absorbance change indicated that the induction of the electron transport reactions was delayed in the ftrb mutant. FTR overexpression also mildly affected the reduction patterns of FBPase and SBPase under high-light conditions, which were accompanied by the modification of electron transport properties. Accordingly, the redox states of FBPase and SBPase were linearly correlated with electron transport rates. In contrast, ATP synthase was highly reduced even when electron transport reactions were not fully induced. Furthermore, the redox response of proton gradient regulation5-like photosynthetic phenotype1 (PGRL1; a protein involved in cyclic electron transport) did not correlate with electron transport rates. Our results provide insights into the working dynamics of the redox regulation system and their differential associations with photosynthetic electron transport efficiency.

Photosynthetic mechanisms underlying NaCl-induced salinity tolerance in rice (Oryza sativa)

BackgroundSalinity stress is an environmental constraint that normally develops concurrently under field conditions, resulting in drastic limitation of rice plant growth and grain productivity. The objective of this study was to explore the alleviating effects of NaCl pre-treatment on rice seedlings as well as the salt tolerance mechanisms by evaluating morph-physiological traits.ResultsVariety Huanghuazhan, either soaked in distilled water or 25 mg/L Prohexadione calcium (Pro-Ca), were first hardened with varying concentrations of NaCl solutions (0 and 50 mM NaCl), and then subjected to varying degrees of salt stress (0 and 100 mM NaCl), indicated by S0, S1, S2 and S3, respectively. Growth analysis suggested that NaCl-pretreatment improved the root/shoot ratio in water-soaked rice plant at DAP 0. Data related to the reaction center density, photosynthetic electron transport efficiency, trapping efficiency were compared before (CK) using performance Index (PIabs). Compared to S2 (Pro-Ca-S2) treatment, PIabs did not show any difference with plants pre-treated with NaCl (S3 or Pro-Ca-S3). Rather than PIabs, significant difference was found in photosynthetic electron transport efficiency (ΨEo). The ΨEo value in Pro-S2 was significantly lowered as compared to Pro-S3 treatment at DAP 7, and the decrease rate was about 6.5%. Correlation analysis indicated leaf PIabs was weak correlated with plant biomass while the quantum yield for reduction of the PSI end electron acceptors, trapped energy flux per reaction center and PSII antenna size displayed strong positive correlation with biomass. Additional analysis revealed that 100 mM NaCl significantly reduced leaf linear electron flux under low-light conditions, regardless of whether seedlings had been pre-treated with 50 mM NaCl or not.ConclusionsNaCl-induced salt tolerance was related to the robust photosynthetic machinery.

Integrating Chlorophyll a Fluorescence and Enzymatic Profiling to Reveal the Wheat Responses to Nano-ZnO Stress.

It has been shown that increased concentrations of zinc oxide nanoparticles (nano-ZnO) in the soil are harmful to plant growth. However, the sensitivity of different wheat cultivars to nano-ZnO stress is still unclear. To detect the physiological response process of wheat varieties with different tolerance to nano-ZnO stress, four wheat cultivars (viz., cv. TS1, ZM18, JM22, and LM6) with different responses to nano-ZnO stress were selected, depending on previous nano-ZnO stress trials with 120 wheat cultivars in China. The results found that nano-ZnO exposure reduced chlorophyll concentrations and photosynthetic electron transport efficiency, along with the depressed carbohydrate metabolism enzyme activities, and limited plant growth. Meanwhile, the genotypic variation in photosynthetic carbon assimilation under nano-ZnO stress was found in wheat plants. Wheat cv. JM22 and LM6 possessed relatively lower Zn concentrations and higher leaf nitrogen per area, less reductions in their net photosynthetic rate, a maximum quantum yield of the PS II (Fv/Fm), electron transport flux per cross-section (ETo/CSm), trapped energy flux per cross-section (TRo/CSm), and total soluble sugar and sucrose concentrations under nano-ZnO stress, showing a better tolerance to nano-ZnO stress than wheat cv. TS1 and ZM18. In addition, the chlorophyll a fluorescence parameters Fv/Fm, ETo/CSm, and TRo/CSm could be used to rapidly screen wheat varieties resistant to nano-ZnO stress. The results here provide a new approach for solving the issues of crop yield decline in regions polluted by heavy metal nanoparticles and promoting the sustainable utilization of farmland with heavy metal pollution.

Exogenous Melatonin Alleviates the Inhibitory Effect of NaHCO3 on Tomato Growth by Regulating the Root pH Value and Promoting Plant Photosynthesis

Soil salinity is a severe threat to agricultural production. Most saline soils turn alkaline, increasing the soil pH and, in turn, hampering the growth and development of crops. In this study, the effects of a foliar spray of melatonin (MT; 100 μmol·L−1) on the pH of the root environment, growth of tomato seedlings, endogenous MT levels, rapid chlorophyll fluorescence induction kinetics, and key enzymes of the Calvin cycle under alkaline (60 mmol·L−1 NaHCO3) stress were studied in Riegel 87-5 tomatoes. The results revealed that the growth and photosynthesis of tomato seedlings were inhibited by increased pH in the root environment under alkali stress; however, the application of exogenous MT reduced the pH of the root environment, alleviated the inhibition of growth of tomato seedlings under alkali stress, increased the content of photosynthetic pigments, alleviated the damage of the donor and acceptor sides of the photosynthetic electron transport chain, increased the activity and efficiency of photosynthetic electron transport, and optimized the share of the light energy allocated to PSII reaction centers. Increased expression levels of Calvin-cycle enzymes, including fructose-1,6-bisphosphate aldolase (FBA), fructose-1,6-bisphosphate esterase (FBP), and phosphoglycerate kinase (PGK), led to enhanced photosynthetic performance in tomato seedlings. Exogenous MT boosted endogenous MT levels and stimulated the production and secretion of organic acids in the root system. This regulation of organic acid content reduced the environmental pH in the inter-root zone, alleviating the damage caused by alkali stress. This study indicated that the exogenous administration of MT may mediate an increase in endogenous MT levels, regulate the efficiency of photosynthesis and root pH levels, and play a crucial role in mitigating injury caused by alkali stress in tomato seedlings.

Photosynthetic Apparatus of Hydrocharis morsus-ranae in Different Solar Lighting.

Hydrocharis morsus-ranae is a free-floating species growing in lakes and slow-flowing rivers near the shore in Europe and Western Asia, and as an invasive plant in the USA and Canada. Light-requiring plants of this species can also grow in the shade, up to about 30% of full sunlight. In this paper we present the data about the photosynthetic apparatus of sunny and shady H. morsus-ranae plants grown in the sun and in the shade in nature. Methods of light and transmission electron microscopy, biochemistry, chlorophyll fluorescence induction as well as the principal component analysis were used. It was found that leaves of plants growing in shade differed from those in the sun with such traits as thickness of a blade, palisade and spongy parenchyma, ultrastructure of chloroplasts, and quantum efficiency of photosynthetic electron transport, the content of chlorophylls and carotenoids, anthocyanins and phenilpropanoids. By these traits, H. morsus-ranae shady plants are similar with shade-bearing plants that indicates their adaptation to light intensity lowering. The ordination plots (PCA) suggested a clear structural and functional shift of plants growing in different lighting showing relationship to light changes in the natural environment. Thus, our results displayed the high phenotypic plasticity of the H. morsus-ranae photosynthetic apparatus, which ensures its acclimation to changing light environment and wide distribution of this species.

Metabolomics revealed the photosynthetic performance and metabolomic characteristics of Euglena gracilis under autotrophic and mixotrophic conditions

Photosynthetic and metabolomic performance of Euglena gracilis was examined and compared under autotrophic and mixotrophic conditions. Autotrophic protozoa (AP) obtained greater biomass (about 33% higher) than the mixotrophic protozoa (MP) after 12 days of growth. AP maintained steady photosynthesis, while MP showed a remarkable decrease in photosynthetic efficiency and dropped to an extremely low level at day 12. In MP, low light absorption and photosynthetic electron transport efficiency, and high energy dissipation were reflected by the chlorophyll (chl a) fluorescence (OJIP) of the protozoa. The values of ΨO, ΦEo, and ETO/RC of MP decreased to extremely low levels, to 1/15, 1/46, and 1/9 those of AP, respectively, while DIO/RC increased to approximately 16 times that of AP. A total of 137 metabolites were showed significant differences between AP and MP. AP accumulated more monosaccharide, lipids, and alkaloids, while MP produced more amino acids, peptides, and long-chain fatty acids including poly-unsaturated fatty acids. The top nine most important enriched pathways obtained from KEGG mapping were related to ABC transporters, biosynthesis of amino acids, purine metabolism, and carbohydrate metabolism. There were significant differences between AP and MP in photosynthetic activity, metabolites, and metabolic pathways. This work presented useful information for the production of high value bioproducts in E. gracilis cultured under different nutritional conditions.

Osmotic regulation and chlorophyll fluorescence characteristics in leaves of wheat seedlings under different salt stresses

The damage mechanism of salt stress on plants has attracted much attention. In order to reveal the damage mechanism of different salt stresses, we compared osmotic regulation and photosynthetic characteristics of seedlings of wheat cultivar Xianhan 3 under sodium salt (150 mmol·L-1) and calcium salt (5, 30 mmol·L-1) treatments alone or in combination. The results showed that sodium salt or calcium salt stress alone significantly inhibited the growth of roots and stems, but increased the amount of soluble sugar and proline, regulatory energy-dissipated electron yield, non-photochemical quenching and relative content of zeaxanthin contents in leaves. In contrast, salt treatments alone significantly decreased the levels of chlorophyll a and chlorophyll b, maximum photochemical efficiency, PSⅡ photochemical efficiency, photochemical quenching and photosynthetic electron transport efficiency. Furthermore, the inhibition of wheat seedling growth was more sensitive to calcium salt than to sodium salt stress, whereas the decreases of chlorophyll content and chlorophyll fluorescence parameters were more prominent in response to sodium salt stress. Except for the amount of soluble protein, lutein and the relative level of zeaxanthin, the changes of other parameters in the leaves due to sodium salt stress were effectively blocked by the application of low calcium concentration, but further increased by the presence of high calcium salt concentration. Taken together, sodium or calcium salt stress alone significantly inhibited seedling growth. The toxicity of sodium salt to wheat seedlings was effectively alleviated by low calcium concentration, but was aggravated by high calcium concentration, which were associated with the changes of photosynthetic pigment content, light energy capture, and photosynthetic electron transport process in the leaves of wheat seedlings. Moreover, osmotic regulators played an important role in enhancing the resistance of wheat seedlings to sodium or/and calcium environment.

Physiological and proteomics analyses reveal the resistance response mechanism to alkali stress in the early seedlings (cotyledons vs. roots) of castor plant (Ricinus communis L.)

Soil alkalinity is a major environmental problem influencing plant growth and productivity in northeastern China. Castor plant (Ricinus communis) is one of the most important oilseed crops worldwide, and has good salt tolerance. The early seedling stage is extremely vulnerable to abiotic stresses, but little is known about the physiological and molecular mechanisms involved in the cotyledons and roots of castor seedlings under alkali stress. In this study, biomass, photosynthesis, root vitality, inorganic ions, organic solutes and antioxidant enzyme activities were measured. Two-dimensional gel electrophoresis-based proteomic approaches were also applied to identify differentially abundant proteins in alkali-treated seedlings. The results showed that alkali stress strongly inhibited seedling growth, especially of the roots. Na+ content increased with increasing alkalinity, and the roots had much higher Na+ and lower K+ than cotyledons. The proline and soluble sugars were both increased in cotyledons, but kept unchanged in the roots under alkali stress. Moreover, proteomic analysis revealed a total of 15 and 25 alkali-responsive proteins in the cotyledons and roots, respectively. For cotyledons, most of the identified proteins were involved in photosynthesis, stress and defense (＞10 %), while those for roots were mainly involved in carbohydrate and energy metabolism, genetic information, stress and defense (＞10 %). These results suggest that cotyledons and roots respond differently to alkali stress. Cotyledons retain efficiency of photosynthetic electron transport and accumulation of osmolytes, while the roots enhance transfer efficiency of the mitochondrial electron transport chain, adjust fatty acid biosynthesis, and promote phosphatidic acid biosynthesis under alkali stress. Additionally, the co-increased abundance of chaperonins indicated that both cotyledons and roots maintained folding of proteins into their proper 3D structures in response to alkali stress. These findings provide new insights into different physiological mechanisms in cotyledon and root responses to alkali stress during the early seedling stage in castor.

Melatonin Alleviates Drought-Induced Damage of Photosynthetic Apparatus in Maize Seedlings

Melatonin plays an important role in the enhancement of plant tolerance to drought stress. The underlying mechanisms of this melatonin-induced protection of the photosynthetic apparatus against drought stress are still not fully understood in maize (Zea mays L.). This study investigated the effects of 100 and 200 μM exogenous melatonin additions on the photosynthetic electron transport process in maize seedlings under drought stress. The chlorophyll a fluorescence transient (OJIP) and modulated 820 nm reflection (MR) analysis showed that drought stress damaged the donor and acceptor side of photosystem II (PSII). Furthermore, the function of PSII reaction centers and the quantum yields of PSI and PSII were significant reduced. These fluorescence parameters were restored in melatonin-treated plants. Energy conversion analysis indicated that melatonin-treated plants maintained a stronger ability to ensure high photosynthetic capacity, as evidenced by higher PSI photochemical quantum yield Y(I) and PSII photochemical quantum yield Y(II). Melatonin treatment decreased the regulated energy dissipation Y(NPQ) and non-regulated energy dissipation Y(NO) in PSII. Moreover, melatonin treatment mitigated the limitations of both the acceptor-side and donor-side of PSI under drought stress, as indicated by lower PSI acceptor side limitation Y(NA) and PSI donor side limitation Y(ND). In addition, 100 μM melatonin was the more effective concentration to alleviate the damage to the photosynthetic apparatus. Thus, exogenous melatonin alleviated the drought stress-induced damage of the photosynthetic apparatus in maize by improving the photosynthetic electron transport efficiency between both photosystems and by enhancing the quantum yields of PSI and PSII photochemistry.

Nano-ZnO priming induces salt tolerance by promoting photosynthetic carbon assimilation in wheat

ABSTRACT High salt seriously reduces plant growth in wheat by depressing photosynthetic carbon assimilation. In this study, wheat plants were firstly primed with nano-ZnO (50 mg L−1), and after 20-day recovery, the plants were then exposed to a 10-day salt stress (200 mM NaCl). The nano-ZnO priming significantly reduced Na concentration and increased leaf water potential under salt stress. In relation to the non-primed plants, the nano-ZnO primed plants possessed more effective oxygen scavenging system as exemplified by the enhanced activities of SOD, APX and CAT, leading to a better maintenance in homeostasis of ROS production under salt stress. The nano-ZnO priming benefited the tolerance of photosynthetic apparatus to subsequent salt stress, which was mainly due to the enhanced trapped energy flux and electron transport flux. The nano-ZnO priming increased the activities of phosphoglucomutase and cytoplasmic invertase, which promoted the sucrose biosynthesis in leaves under salt stress. In addition, the nano-ZnO primed plants had higher shoot dry weight than the non-primed plants under salt stress. Collectively, nano-ZnO priming activated the antioxidant system to depress the oxidative burst and enhanced the efficiency of photosynthetic electron transport and sucrose biosynthesis in leaves under salt stress, hereby improved the salt tolerance in wheat.

Physiological and iTRAQ based proteomics analyses reveal the mechanism of elevated CO2 concentration alleviating drought stress in cucumber (Cucumis sativus L.) seedlings

Carbon dioxide is one of the most important anthropogenic greenhouse gases. We previously confirmed that elevated [CO2] alleviated the negative consequences of drought stress to cucumber seedlings, but the physiological mechanism remains unknown. We investigated the morphological and physiological characteristics as well as iTRAQ-based proteomics analyses in this study under different combinations [CO2] (400 and (800 ± 20) μmol·mol−1) and water conditions (no, moderate and severe drought stress simulated by polyethylene glycol 6000). The results showed: (1) elevated [CO2] significantly increased plant height, stem diameter, leaf area and relative water content (RWC) under drought stress; (2) drought stress significantly increased J and K peaks of the chlorophyll a fluorescence transient, indicating the damage of photosynthetic electron transport chain, while elevated [CO2] decreased them especially under moderate drought condition; (3) iTRAQ-based proteomics analyses indicated that elevated [CO2] increased the abundance of psbJ and the PSI reaction center subunit VI-2 in seedlings exposed to moderate drought stress; (4) the abundance of uroporphyrinogen decarboxylase 2 and tetrapyrrole-binding protein decreased in response to elevated [CO2] under severe drought condition; (5) elevated [CO2] regulated the expression of chloroplast proteins such as those related to stress and defense response, redox homeostasis, metabolic pathways. In conclusion, elevated [CO2] enhanced the efficiency of photosynthetic electron transport, limited the absorption of excess light energy, enhanced the ability of antioxidant and osmotic adjustment, and alleviated the accumulation of toxic substances under drought stress. These findings provide new clues for understanding the molecular basis of elevated [CO2] alleviated plant drought stress.

An Altered Circadian Clock Coupled with a Higher Photosynthesis Efficiency Could Explain the Better Agronomic Performance of a New Coffee Clone When Compared with a Standard Variety.

In a context where climate change is threatening coffee productivity, the management of coffee leaf rust is a challenging issue. Major resistant genes, which have been used for many years, are systematically being overcome by pathogens. Developing healthy plants, able to defend themselves and be productive even when attacked by the pathogen, should be part of a more sustainable alternative approach. We compared one hybrid (GPFA124), selected for its good health in various environments including a reduced rust incidence, and the cv. ‘Caturra’, considered as a standard in terms of productivity and quality but highly susceptible to rust, for phenotypic variables and for the expression of genes involved in the circadian clock and in primary photosynthetic metabolism. The GPFA124 hybrid showed increased photosynthetic electron transport efficiency, better carbon partitioning, and higher chlorophyll content. A strong relationship exists between chlorophyll a fluorescence and the expression of genes related to the photosynthetic electron transport chain. We also showed an alteration of the amplitude of circadian clock genes in the clone. Our work also indicated that increased photosynthetic electron transport efficiency is related to the clone’s better performance. Chlorophyll a fluorescence measurement is a good indicator of the coffee tree’s physiological status for the breeder. We suggest a connection between the circadian clock and carbon metabolism in coffee tree.

Photosynthetic capacity, osmotic adjustment and antioxidant system in sugar beet (Beta vulgaris L.) in response to alkaline stress

Photosynthetic characteristics of sugar beet cultivars KWS0143 and Beta464 were studied under alkaline conditions, including 0 (A0, control), 25 (A1), 50 (A2), 75 (A3), and 100 mM of mixed alkali (Na2CO3:NaHCO3, 1:2). A2, A3, and A4 reduced net photosynthetic rate (PN), stomatal conductance, and transpiration rate, but rose intercellular CO2 concentration. Reduction in PN occurred probably due to nonstomatal limitation. The decrease in efficiency of photosynthetic electron transport might be the main reason for the decrease of PN. The concentrations of photosynthetic pigments were significantly reduced by high (A3 and A4) alkalinity. Changes in chloroplast ultrastructure are the reason for the decrease in chlorophyll content. Sugar beet could resist injury from alkali owing to osmotic substances and antioxidant enzymes if alkaline stress was at a lower level. The better performance of KWS0143 under alkalinity might be associated with its more efficient osmotic and antioxidant systems to resist injury of photosynthetic apparatus caused by alkalinity.

Cold Tolerance of Photosynthetic Electron Transport System Is Enhanced in Wheat Plants Grown Under Elevated CO2.

The effects of CO2 elevation on sensitivity of photosynthetic electron transport system of wheat in relation to low temperature stress are unclear. The performance of photosynthetic electron transport system and antioxidant system in chloroplasts was investigated in a temperature sensitive wheat cultivar Lianmai6 grown under the combination of low temperature (2 days at 2/−1°C in the day/night) and CO2 elevation (800 μmol l−1). It was found that CO2 elevation increased the efficiency of photosynthetic electron transport in wheat exposed to low temperature stress, which was related to the enhanced maximum quantum yield for electron transport beyond QA and the increased quantum yield for reduction of end electron acceptors at the PSI acceptor side in plants under elevated CO2. Also, under low temperature, the activities of ATPases, ascorbate peroxidase, and catalase in chloroplasts were enhanced in wheat under elevated CO2. It suggested that the cold tolerance of photosynthetic electron transport system is enhanced by CO2 elevation.

Fast reactivation of photosynthesis in arctic phytoplankton during the polar night1.

Arctic microalgae experience long periods of continuous darkness during the polar night, when they are unable to photosynthesize. Despite numerous studies on overwintering strategies, such as utilization of stored energy products, formation of resting stages, reduction of metabolic rates and heterotrophic lifestyles, there have been few attempts to assess the insitu physiological state and restoration of the photosynthetic apparatus upon re-illumination. In this study, we found diverse and active marine phytoplankton communities during the polar night at 78°N. Furthermore, we observed rapid changes (≤20min) in the efficiency of photosynthetic electron transport upon re-illumination. High photosynthetic capacity and net primary production were established after 24h of re-illumination. Our results suggest that some Arctic autotrophs maintain fully functional photosystem II and downstream electron acceptors during the polar night even though the low insitu net primary production levels measured in January prove that light was not sufficient to support any measurable primary production. Due to low temperatures resulting in low respiratory rates as well as the absence of photodamage during the polar night, maintenance of basic photosynthetic machinery may actually pose relatively low metabolic costs for algal cells. This could allow Arctic microalgae to endure the polar night without the formation of dormant stages, enabling them to recover and take advantage of light immediately upon the suns return during the winter-spring transition.

Seasonal regulation of the coupling between photosynthetic electron transport and carbon fixation in the Southern Ocean

AbstractActive fluorescence measurements can provide rapid, non‐intrusive estimates of phytoplankton primary production at high spatial and temporal resolution, but there is uncertainty in converting from electrons to ecologically relevant rates of CO2 assimilation. In this study, we examine the light‐dependent rates of photosynthetic electron transport and 13C‐uptake in the Atlantic sector of the Southern Ocean to derive a conversion factor for both winter (July 2015–August 2015) and summer (December 2015–February 2016). The results revealed significant seasonal differences in the light‐saturated chlorophyll specific rate of 13C‐uptake, ( ), with mean summer values 2.3 times higher than mean winter values, and the light limited chlorophyll specific efficiency, (αB), with mean values 2.7 times higher in summer than in winter. Similar patterns were observed in the light‐saturated photosynthetic electron transport rates ( , 1.5 times higher in summer) and light limited photosynthetic electron transport efficiency (αRCII, 1.3 times higher in summer). The conversion factor between carbon and electrons (Φe:C (mol e− mol C−1)) was derived utilizing in situ measurements of the chlorophyll‐normalized number of reaction centers (nRCII), resulting in a mean summer Φe:C which was ∼ 3 times lower than the mean winter Φe:C. Empirical relationships were established between Φe:C, light and NPQ, however they were not consistent across locations or seasons. The seasonal decoupling of Φe:C is the result of differences in Ek‐dependent and Ek‐independent variability, which require new modelling approaches and improvements to bio‐optical techniques to account for these inter‐seasonal differences in both taxonomy and environmental mean conditions.

RAPTOR Controls Developmental Growth Transitions by Altering the Hormonal and Metabolic Balance.

Vegetative growth requires the systemic coordination of numerous cellular processes, which are controlled by regulatory proteins that monitor extracellular and intracellular cues and translate them into growth decisions. In eukaryotes, one of the central factors regulating growth is the serine/threonine protein kinase Target of Rapamycin (TOR), which forms complexes with regulatory proteins. To understand the function of one such regulatory protein, Regulatory-Associated Protein of TOR 1B (RAPTOR1B), in plants, we analyzed the effect of raptor1b mutations on growth and physiology in Arabidopsis (Arabidopsis thaliana) by detailed phenotyping, metabolomic, lipidomic, and proteomic analyses. Mutation of RAPTOR1B resulted in a strong reduction of TOR kinase activity, leading to massive changes in central carbon and nitrogen metabolism, accumulation of excess starch, and induction of autophagy. These shifts led to a significant reduction of plant growth that occurred nonlinearly during developmental stage transitions. This phenotype was accompanied by changes in cell morphology and tissue anatomy. In contrast to previous studies in rice (Oryza sativa), we found that the Arabidopsis raptor1b mutation did not affect chloroplast development or photosynthetic electron transport efficiency; however, it resulted in decreased CO2 assimilation rate and increased stomatal conductance. The raptor1b mutants also had reduced abscisic acid levels. Surprisingly, abscisic acid feeding experiments resulted in partial complementation of the growth phenotypes, indicating the tight interaction between TOR function and hormone synthesis and signaling in plants.

Melatonin alleviates low PS I-limited carbon assimilation under elevated CO2 and enhances the cold tolerance of offspring in chlorophyll b-deficient mutant wheat.

Melatonin is involved in the regulation of carbohydrate metabolism and induction of cold tolerance in plants. The objective of this study was to investigate the roles of melatonin in modulation of carbon assimilation of wild-type wheat and the Chl b-deficient mutant ANK32B in response to elevated CO2 concentration ([CO2 ]) and the transgenerational effects of application of exogenous melatonin (hereafter identified as melatonin priming) on the cold tolerance in offspring. The results showed that the melatonin priming enhanced the carbon assimilation in ANK32B under elevated [CO2 ], via boosting the activities of ATPase and sucrose synthesis and maintaining a relatively higher level of total chlorophyll concentration in leaves. In addition, melatonin priming in maternal plants at grain filling promoted the seed germination in offspring by accelerating the starch degradation and improved the cold tolerance of seedlings through activating the antioxidant enzymes and enhancing the photosynthetic electron transport efficiency. These findings suggest the important roles of melatonin in plant response to future climate change, indicating that the melatonin priming at grain filling in maternal plants could be an effective approach to improve cold tolerance of wheat offspring at seedling stage.

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.