Project description:The photosynthetic apparatus is one of the major primary sensors of the plant's external environment. Changes in environmental conditions affect the balance between harvested light energy and the capacity to deal with excited electrons in the stroma, which alters the redox homeostasis of the photosynthetic electron transport chain. Disturbances to redox balance activate photosynthetic regulation mechanisms and trigger signalling cascades that can modify the transcription of nuclear genes. H2O2 and oxylipins have been identified as especially prominent regulators of gene expression in response to excess light stress. This paper explores the hypothesis that photosynthetic imbalance triggers specific signals that target discrete gene profiles and biological processes. Analysis of the major retrograde signalling pathways engaged during high light stress and recovery demonstrates both specificity and overlap in gene targets. This work reveals distinct, time-resolved profiles of gene expression that suggest a regulatory interaction between rapidly activated abiotic stress response and induction of secondary metabolism and detoxification processes during recovery. The findings of this study show that photosynthetic electron transport provides a finely tuned sensor for detecting and responding to the environment through chloroplast retrograde signalling. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
Project description:Six weeks old Arabidopsis plants were transferred to a low CO2 (100 ppm) environment during 24 hours and compared to control plants kept under ambient CO2 conditions. Limited CO2 availability will cause higher rates of photorespiration and affect the plant redox homeostasis. We studied the transcriptomic impact of exposing plants to a lower CO2 environment to further eliculidate the signaling pathways during photorespiratory stress.
Project description:Rhodopin, rhodopinal, and their glucoside derivatives are carotenoids that accumulate in different amounts in the photosynthetic bacterium, Rhodoblastus (Rbl.) acidophilus strain 7050, depending on the intensity of the light under which the organism is grown. The different growth conditions also have a profound effect on the spectra of the bacteriochlorophyll (BChl) pigments that assemble in the major LH2 light-harvesting pigment-protein complex. Under high-light conditions the well-characterized B800-850 LH2 complex is formed and accumulates rhodopin and rhodopin glucoside as the primary carotenoids. Under low-light conditions, a variant LH2, denoted B800-820, is formed, and rhodopinal and rhodopinal glucoside are the most abundant carotenoids. The present investigation compares and contrasts the spectral properties and dynamics of the excited states of rhodopin and rhodopinal in solution. In addition, the systematic differences in pigment composition and structure of the chromophores in the LH2 complexes provide an opportunity to explore the effect of these factors on the rate and efficiency of carotenoid-to-BChl energy transfer. It is found that the enzymatic conversion of rhodopin to rhodopinal by Rbl. acidophilus 7050 grown under low-light conditions results in nearly 100% carotenoid-to-BChl energy transfer efficiency in the LH2 complex. This comparative analysis provides insight into how photosynthetic systems are able to adapt and survive under challenging environmental conditions.
Project description:Photorespiration (PR) is the pathway that detoxifies the product of the oxygenation reaction of Rubisco. It has been hypothesized that in dynamic light environments, PR provides a photoprotective function. To test this hypothesis, we characterized plants with varying PR enzyme activities under fluctuating and non-fluctuating light conditions. Contrasting our expectations, growth of mutants with decreased PR enzyme levels was least affected in fluctuating light compared with wild type. Results for growth, photosynthesis and metabolites combined with thermodynamics-based flux analysis revealed two main causal factors for this unanticipated finding: reduced rates of photosynthesis in fluctuating light and complex re-routing of metabolic fluxes. Only in non-fluctuating light, mutants lacking the glutamate:glyoxylate aminotransferase 1 re-routed glycolate processing to the chloroplast, resulting in photooxidative damage through H2O2 production. Our results reveal that dynamic light environments buffer plant growth and metabolism against photorespiratory perturbations.
Project description:Plants are often confronted with light fluctuations from seconds to minutes due to altering sun angles, mutual shading, and clouds under natural conditions, which causes a massive carbon loss and water waste. The effect of stomatal morphology on the response of leaf gas exchange to fluctuating light remains disputable. In this study, we investigated the differences in leaf stomatal morphology and photosynthetic induction across twelve rice genotypes after a stepwise increase in light intensity. A negative correlation was observed between stomatal size and density across rice genotypes. Smaller and denser stomata contributed to a faster stomatal response under fluctuating light. Plants with faster stomatal opening also showed faster photosynthetic induction and higher biomass accumulation but lower intrinsic water use efficiency ( i WUE) under fluctuating light. Moreover, stomatal morphology seemed to have less effect on the initial and final stomatal conductance, and there was a minimal correlation between steady-state and non-steady-state stomatal conductance among different rice genotypes. These results highlight the important role of stomatal morphology in regulating photosynthetic efficiency and plant growth under fluctuating light conditions. To simultaneously enhance leaf i WUE when improving the photosynthetic efficiency under fluctuating light, it may be necessary to take biochemical processes into account in the future.
Project description:The response of photosynthetic CO2 assimilation to changes of illumination affects plant growth and crop productivity under natural fluctuating light conditions. However, the effects of nitrogen (N) supply on photosynthetic physiology after transition from low to high light are seldom studied. To elucidate this, we measured gas exchange and chlorophyll fluorescence under fluctuating light in tomato (Solanum lycopersicum) seedlings grown with different N conditions. After transition from low to high light, the induction speeds of net CO2 assimilation (A N ), stomatal conductance (g s ), and mesophyll conductance (g m ) delayed with the decline in leaf N content. The time to reach 90% of maximum A N , g s and g m was negatively correlated with leaf N content. This delayed photosynthetic induction in plants grown under low N concentration was mainly caused by the slow induction response of g m rather than that of g s . Furthermore, the photosynthetic induction upon transfer from low to high light was hardly limited by photosynthetic electron flow. These results indicate that decreased leaf N content declines carbon gain under fluctuating light in tomato. Increasing the induction kinetics of g m has the potential to enhance the carbon gain of field crops grown in infertile soil.
Project description:Crop photosynthesis and yield are limited by slow photosynthetic induction in sunflecks. We quantified variation in induction kinetics across diverse genotypes of wheat for the first time. Following a preliminary study that hinted at wide variation in induction kinetics across 58 genotypes, we grew 10 genotypes with contrasting responses in a controlled environment and quantified induction kinetics of carboxylation capacity (Vcmax) from dynamic A versus ci curves after a shift from low to high light (from 50 µmol m-2 s-1 to 1500 µmol m-2 s-1), in five flag leaves per genotype. Within-genotype median time for 95% induction (t95) of Vcmax varied 1.8-fold, from 5.2 min to 9.5 min. Our simulations suggest that non-instantaneous induction reduces daily net carbon gain by up to 15%, and that breeding to speed up Vcmax induction in the slowest of our 10 genotypes to match that in the fastest genotype could increase daily net carbon gain by up to 3.4%, particularly for leaves in mid-canopy positions (cumulative leaf area index ≤1.5 m2 m-2), those that experience predominantly short-duration sunflecks, and those with high photosynthetic capacities.
Project description:The influence of reduced glycine decarboxylase complex (GDC) activity on leaf atmosphere CO2 and 13CO2 exchange was tested in transgenic Oryza sativa with the GDC H-subunit knocked down in leaf mesophyll cells. Leaf measurements on transgenic gdch knockdown and wild-type plants were carried out in the light under photorespiratory and low photorespiratory conditions (i.e. 18.4 kPa and 1.84 kPa atmospheric O2 partial pressure, respectively), and in the dark. Under approximately current ambient O2 partial pressure (18.4 kPa pO2), the gdch knockdown plants showed an expected photorespiratory-deficient phenotype, with lower leaf net CO2 assimilation rates (A) than the wild-type. Additionally, under these conditions, the gdch knockdown plants had greater leaf net discrimination against 13CO2 (Δo) than the wild-type. This difference in Δo was in part due to lower 13C photorespiratory fractionation (f) ascribed to alternative decarboxylation of photorespiratory intermediates. Furthermore, the leaf dark respiration rate (Rd) was enhanced and the 13CO2 composition of respired CO2 (δ13CRd) showed a tendency to be more depleted in the gdch knockdown plants. These changes in Rd and δ13CRd were due to the amount and carbon isotopic composition of substrates available for dark respiration. These results demonstrate that impairment of the photorespiratory pathway affects leaf 13CO2 exchange, particularly the 13C decarboxylation fractionation associated with photorespiration.
Project description:We report that phosphatidylglycerol (PG) biosynthesis in plastid is required for plastid gene expression mediated by plastid-encoded RNA polymerase and light-induced expression of nuclear-encoded photosynthesis-associated genes. A transcription factor GOLDEN-LIKE1 was also found to be involved in the downregulation of nuclear photosynthesis genes in responce to PG deficiency.
Project description:Leaf temperature changes with incident light intensity, but it is unclear how the concurrent changes influence leaf photosynthesis. We examined the time courses of CO2 gas exchanges and chlorophyll fluorescence of seedling leaves in four tropical tree species in response to lightflecks under three different temperature conditions. The three conditions were two constant temperatures at 30°C (T 30) and 40°C (T 40), and a simulated gradually changing temperature from 30 to 40°C (T dyn). The time required to reach 50% of the full photosynthetic induction under T 40 was similar to, or even larger than, that under T 30. However, the induction of assimilation rate (A) and electron transport rate of photosystem II (ETR II) and Rubisco activation process were generally accelerated under T dyn compared to those at either T 30 or T 40. The acceleration in photosynthetic induction under T dyn was significantly greater in the shade-tolerant species than in the shade-intolerant species. A modified photosynthetic limitation analysis indicated that the acceleration was likely to be mainly due to ETR II at the early stage of photosynthetic induction. The study suggests that concurrent increases in leaf temperature with light may increase leaf carbon gain under highly fluctuating light in tropical tree seedlings, particularly in shade-tolerant species.