Photosynthetic Acclimation Research Articles

Different Strategies for Photosynthetic Regulation under Fluctuating Light in Two Sympatric Paphiopedilum Species.

Fluctuating light can cause selective photoinhibition of photosystem I (PSI) in angiosperms. Cyclic electron flow (CEF) around PSI and electron flux from water via the electron transport chain to oxygen (the water-water cycle) play important roles in coping with fluctuating light in angiosperms. However, it is unclear whether plant species in the same genus employ the same strategy to cope with fluctuating light. To answer this question, we measured P700 redox kinetics and chlorophyll fluorescence under fluctuating light in two Paphiopedilum (P.) Pftzer (Orchidaceae) species, P. dianthum and P. micranthum. After transition from dark to high light, P. dianthum displayed a rapid re-oxidation of P700, while P. micranthum displayed an over-reduction of P700. Furthermore, the rapid re-oxidation of P700 in P. dianthum was not observed when measured under anaerobic conditions. These results indicated that photo-reduction of O2 mediated by the water-water cycle was functional in P. dianthum but not in P. micranthum. Within the first few seconds after an abrupt transition from low to high light, PSI was highly oxidized in P. dianthum but was highly reduced in P. micranthum, indicating that the different responses of PSI to fluctuating light between P. micranthum and P. dianthum was attributed to the water-water cycle. In P. micranthum, the lack of the water-water cycle was partially compensated for by an enhancement of CEF. Taken together, P. dianthum and P. micranthum employed different strategies to cope with the abrupt change of light intensity, indicating the diversity of strategies for photosynthetic acclimation to fluctuating light in these two closely related orchid species.

Photosynthetic acclimation during low-light-induced leaf senescence in post-anthesis maize plants.

Low light conditions not only induce leaf senescence, but also photosynthetic acclimation. This study aimed to determine whether plants exhibit photosynthetic acclimation during low-light-induced leaf senescence. The influences of shading on leaf senescence and photosynthetic acclimation were explored in post-anthesis maize plants. The results showed that whole shading (WS) of maize plants accelerated leaf senescence, whereas partial shading (PS) slowed leaf senescence. WS led to larger decreases in the photosynthetic rate (Pn) and stomatal conductance (Gs) compared to those of the PS treatment. Interestingly, chlorophyll afluorescence (ChlF) demonstrated that the absorption flux (ABS/CSo) and trapped energy flux (TRo/CSo) per cross section in leaves remained relatively stable under WS, whereas significant decreases in the active PSII reaction centers (RC/CSo) resulted in considerable increases in absorption (ABS/RC) and trapped energy flux (TRo/RC) per reaction center. ABS/CSo, TRo/CSo, ABS/RC, and TRo/RC increased markedly under PS, whereas there were slight decreases in RC/CSo and electron transport activity. These results suggest that the PS treatment resulted in obvious improvements in the absorption and capture of light energy in shaded leaves. Further analysis demonstrated that both the WS and PS treatments resulted in a greater decrease in the activity of Rubisco compared to that of phosphoenolpyruvate carboxylase (PEPC). Moreover, PEPC activity in PS was maintained at a high level. Consequently, the current study proposed that the improvement of the absorption and capture of light energy and the maintenance of PEPC activity of mesophyll cells were due to photosynthetic acclimation of low-light-induced leaf senescence in maize plants. In addition, the rate of senescence of vascular bundle cells in maize leaves exceeded that of mesophyll cells under low light, showing obvious tissue specificity.

Warming and elevated CO2 alter tamarack C fluxes, growth and mortality: evidence for heat stress-related C starvation in the absence of water stress.

Climate warming is increasing the frequency of climate-induced tree mortality events. While drought combined with heat is considered the primary cause of this mortality, little is known about whether moderately high temperatures alone can induce mortality, or whether rising CO2 would prevent mortality at high growth temperatures. We grew tamarack (Larix laricina) under ambient (400p.p.m.) and elevated (750p.p.m.) CO2 concentrations combined with ambient, ambient +4 °C and ambient +8 °C growth temperatures to investigate whether high growth temperatures lead to carbon (C) limitations and mortality. Growth at +8 °C led to 40% mortality in the ambient CO2 (8TAC) treatment, but no mortality in the elevated CO2 treatment. Thermal acclimation of respiration led to similar leaf C balances across the warming treatments, despite a lack of photosynthetic acclimation. Photosynthesis was stimulated under elevated CO2, increasing seedling growth, but not leaf C concentrations. However, growth and foliar C concentrations were lowest in the +8 °C treatments, even with elevated CO2. Dying 8TAC seedlings had lower needle C concentrations and lower ratios of photosynthesis to respiration than healthy 8TAC seedlings, indicating that C limitations were likely the cause of seedling mortality under high growth temperatures.

Growth and Photosynthetic Responses of Seedlings of Japanese White Birch, a Fast-Growing Pioneer Species, to Free-Air Elevated O3 and CO2

Plant growth is not solely determined by the net photosynthetic rate (A), but also influenced by the amount of leaves as a photosynthetic apparatus. To evaluate growth responses to CO2 and O3, we investigated the effects of elevated CO2 (550–560 µmol mol−1) and O3 (52 nmol mol−1; 1.7 × ambient O3) on photosynthesis and biomass allocation in seedlings of Japanese white birch (Betula platyphylla var. japonica) grown in a free-air CO2 and O3 exposure system without any limitation of root growth. Total biomass was enhanced by elevated CO2 but decreased by elevated O3. The ratio of root to shoot (R:S ratio) showed no difference among the treatment combinations, suggesting that neither elevated CO2 nor elevated O3 affected biomass allocation in the leaf. Accordingly, photosynthetic responses to CO2 and O3 might be more important for the growth response of Japanese white birch. Based on A measured under respective growth CO2 conditions, light-saturated A at a light intensity of 1500 µmol m−2 s−1 (A1500) in young leaves (ca. 30 days old) exhibited no enhancement by elevated CO2 in August, suggesting photosynthetic acclimation to elevated CO2. However, lower A1500 was observed in old leaves (ca. 60 days old) of plants grown under elevated O3 (regulated to be twice ambient O3). Conversely, light-limited A measured under a light intensity of 200 µmol m−2 s−1 (A200) was significantly enhanced by elevated CO2 in young leaves, but suppressed by elevated O3 in old leaves. Decreases in total biomass under elevated O3 might be attributed to accelerated leaf senescence by O3, indicated by the reduced A1500 and A200 in old leaves. Increases in total biomass under elevated CO2 might be attributed to enhanced A under high light intensities, which possibly occurred before the photosynthetic acclimation observed in August, and/or enhanced A under limiting light intensities.

Photosynthetic Acclimation and Growth Responses to Elevated CO2 Associate with Leaf Nitrogen and Phosphorus Concentrations in Mulberry (Morus multicaulis Perr.)

Mulberry (Morus spp.) is a multipurpose tree that is worldwide planted because of its economic importance. This study was to investigate the likely consequences of anticipated future elevated CO2 (eCO2) on growth, physiology and nutrient uptake of nitrogen (N), phosphorus (P) and potassium (K) in two most widely cultivated mulberry (Morus multicaulis Perr.) varieties, QiangSang-1 and NongSang-14, in southwest China. A pot experiment was conducted in environmentally auto-controlled growth chambers under ambient CO2 (ACO2, 410/460 ppm, daytime/nighttime) and eCO2 (710/760 ppm). eCO2 significantly increased plant height, stem diameter, leaf numbers and biomass production, and decreased chlorophyll concentrations, net photosynthetic rate, stomatal conductance and transpiration rate of these two mulberry varieties. Under eCO2 leaf N and P, and root N, P and K concentrations in both mulberry varieties decreased, while plant total P and K uptake in both varieties were enhanced, and an increased total N uptake in NongSang-4, but not in QiangSang-1. Nutrient dilution and transpiration rate were the main factors driving the reduction of leaf N and P, whereas changes in plant N and P demand had substantial impacts on photosynthetic inhibition. Our results can provide effective nutrient management strategies for a sustainable mulberry production under global atmosphere CO2 rising scenarios.

A Holistic Approach to Study Photosynthetic Acclimation Responses of Plants to Fluctuating Light.

Plants in natural environments receive light through sunflecks, the duration and distribution of these being highly variable across the day. Consequently, plants need to adjust their photosynthetic processes to avoid photoinhibition and maximize yield. Changes in the composition of the photosynthetic apparatus in response to sustained changes in the environment are referred to as photosynthetic acclimation, a process that involves changes in protein content and composition. Considering this definition, acclimation differs from regulation, which involves processes that alter the activity of individual proteins over short-time periods, without changing the abundance of those proteins. The interconnection and overlapping of the short- and long-term photosynthetic responses, which can occur simultaneously or/and sequentially over time, make the study of long-term acclimation to fluctuating light in plants challenging. In this review we identify short-term responses of plants to fluctuating light that could act as sensors and signals for acclimation responses, with the aim of understanding how plants integrate environmental fluctuations over time and tailor their responses accordingly. Mathematical modeling has the potential to integrate physiological processes over different timescales and to help disentangle short-term regulatory responses from long-term acclimation responses. We review existing mathematical modeling techniques for studying photosynthetic responses to fluctuating light and propose new methods for addressing the topic from a holistic point of view.

Morphological development and photosynthetic acclimation of Panax ginseng seedlings to irradiation by light-emitting diodes (LEDs)

To determine the optimal light intensity and enable plants to cope with various environmental stresses in plant factories, the morphological and photosynthetic characteristics of ginseng seedlings, including the secondary metabolites, were investigated under six light intensities: 25, 50, 75, 100, 125, and 150 μmol m−2 s−1. The shoot length increased with lower light intensity up to 75 μmol m−2 s−1, and the leaf area and specific leaf weight were greatest at 100 and 75 μmol m−2 s−1, respectively. Stomata frequency was higher from 100 μmol m−2 s−1 with higher light intensity, and single stomatal pore length also increased at 150 μmol m−2 s−1. Net photosynthetic rate at light saturation and net photosynthetic rate in growth condition increased sequentially up to 100 μmol m−2 s−1 before rapidly decreasing at 150 μmol m−2 s−1. The dark respiration rate and light compensation point were significantly high at 150 μmol m−2 s−1 only. Fv/Fm and chlorophyll content statistically differed from 63 and 84 days after seedling stand, respectively. Thus, the leaves withered to death with higher light intensity. The ginsenoside content in the roots significantly increased according to the light intensity, and the panaxadiol/panaxatriol (PT) ratio tended to decrease as the PT-type ginsenosides increased further. Taken together, the range of 75–100 μmol m−2 s−1 was found to be beneficial for growth, photosynthetic acclimation response, and total accumulated ginsenosides of ginseng seedlings.

Photosynthetic plasticity of a tropical tree species, Tabebuia rosea, in response to elevated temperature and [CO2

Atmospheric and climate change will expose tropical forests to conditions they have not experienced in millions of years. To better understand the consequences of this change, we studied photosynthetic acclimation of the neotropical tree species Tabebuia rosea to combined 4°C warming and twice-ambient (800 ppm) CO2 . We measured temperature responses of the maximum rates of ribulose 1,5-bisphosphate carboxylation (VCMax ), photosynthetic electron transport (JMax ), net photosynthesis (PNet ), and stomatal conductance (gs ), and fitted the data using a probabilistic Bayesian approach. To evaluate short-term acclimation plants were then switched between treatment and control conditions and re-measured after 1-2 weeks. Consistent with acclimation, the optimum temperatures (TOpt ) for VCMax , JMax and PNet were 1-5°C higher in treatment than in control plants, while photosynthetic capacity (VCMax , JMax , and PNet at TOpt ) was 8-25% lower. Likewise, moving control plants to treatment conditions moderately increased temperature optima and decreased photosynthetic capacity. Stomatal density and sensitivity to leaf-to-air vapour pressure deficit were not affected by growth conditions, and treatment plants did not exhibit stronger stomatal limitations. Collectively, these results illustrate the strong photosynthetic plasticity of this tropical tree species as even fully developed leaves of saplings transferred to extreme conditions partially acclimated.

Future CO2 , warming and water deficit impact white and red Tempranillo grapevine: Photosynthetic acclimation to elevated CO2 and biomass allocation.

Due to the CO2 greenhouse effect, elevated atmospheric concentration leads to higher temperatures, accompanied by episodes of less water availability in semiarid and arid areas or drought periods. Studies investigating these three factors (CO2 , temperature and water availability) simultaneously in grapevine are scarce. The present work aims to analyze the combined effects of high CO2 (700 ppm), high temperature (ambient +4°C) and drought on the photosynthetic activity, biomass allocation, leaf non-structural carbon composition, and carbon/nitrogen (C/N) ratio in grapevine. Two grapevine cultivars, red berry Tempranillo and white berry Tempranillo, were used, the latter being a natural, spontaneous mutant of the red cultivar. The experiment was performed on fruit-bearing cuttings during a 3-month period, from June (fruit set) to August (maturity). The plants were grown in research-oriented facilities, temperature-gradient greenhouses, where temperature, CO2 , and water supply can be modified in a combined way. Drought had the strongest effect on biomass accumulation compared to the other environmental variables, and root biomass allocation was increased under water deficit. CO2 and temperature effects were smaller and depended on cultivar, and on interactions with the other factors. Acclimation effects were observed on both cultivars as photosynthetic rates under high atmospheric CO2 were reduced by long-term exposition to elevated CO2 . Exposure to such high CO2 resulted in increased starch concentration and reduced C/N ratio in leaves. A correlation between the intensity of the reduction in photosynthetic rates and the accumulation of starch in the leaves was found after prolonged exposure to elevated CO2 .

Leaf morpho-anatomical traits in Vigna radiata L. affect plant photosynthetic acclimation to changing vapor pressure deficit

Vapor Pressure Deficit (VPD) influences plant photosynthesis and the hydraulic behaviour associated with stomata regulation. However, it is not clear whether and how changes in leaf morpho-anatomical traits drive photosynthetic acclimation to VPD. Here, we examined the role of leaf anatomy in the eco-physiological responses of Vigna radiata L. to VPD changes in controlled environment. Plants were grown under two VPD levels (high-VPD, HV; low-VPD, LV) and then transferred to the opposite conditions (high-to-low, HLV; low-to-high, LHV). We hypothesised that growth under different VPDs may determine anatomical changes that could affect plant physiological plasticity to VPD variations. HV plant growth (height, leaf area, number of leaves) and gas-exchange (net-photosynthesis, stomatal conductance, water use efficiency) were reduced in a range of 16–47 % compared to LV. This was mostly attributed to reduction in stomatal and vein density and lower stomatal conductance. After transferring these plants to a more favourable environment (HLV), they showed unchanged photosynthesis and conductance while LHV plants reduced their gas-exchange rates to control water loss under high evaporative demand. Morpho-anatomical traits (high density and smaller stomata, higher vein density) in LHV plants showed higher physiological plasticity. Therefore, physiological plasticity induced by anatomical traits should be considered when evaluating how plants would cope with environmental changes in a climate change scenario.

Responses of Forest Carbon Cycle to Drought and Elevated CO2

Forests play a pivotal role in mitigating global warming as an important carbon sink. Recent global greening trends reflect a positive influence of elevated atmospheric CO2 on terrestrial carbon uptake. However, increasingly frequent and intense drought events endanger the carbon sequestration function of forests. This review integrates previous studies across scales to identify potential global trends in forest responses to drought and elevated CO2 as well as to identify data needs in this important research field. The inconsistent responses of ecosystem respiration to drought contributes to the change of forest net CO2 exchange, which depends on the balance of opposite effects of warming and water stress on respiration. Whether CO2 fertilization can offset the effects of drought remains controversial, however, we found a potential overestimation of global CO2 fertilization effects because of increasing water stress and other limitations such as light and nutrients (N, P) as well as the possibility of photosynthetic acclimation.

Regulation of Phaeodactylum plastid gene transcription by redox, light, and circadian signals.

Diatoms are a diverse group of photosynthetic unicellular algae with a plastid of red-algal origin. As prolific primary producers in the ocean, diatoms fix as much carbon as all rainforests combined. The molecular mechanisms that contribute to the high photosynthetic productivity and ecological success of diatoms are however not yet fully understood. Using the model diatom Phaeodactylum tricornutum, here we show rhythmic transcript accumulation of plastid psaA, psbA, petB, and atpB genes as driven by a free running circadian clock. Treatment with the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea overrides the circadian signal by markedly downregulating transcription of psaA, petB, and atpB genes but not the psbA gene. Changes in light quantity produce little change in plastid gene transcription while the effect of light quality seems modest with only the psaA gene responding in a pattern that is dependent on the redox state of the plastoquinone pool. The significance of these plastid transcriptional responses and the identity of the underlying genetic control systems are discussed with relevance to diatom photosynthetic acclimation.

Warm air temperatures increase photosynthetic acclimation to elevated CO2 concentrations in rice under field conditions

Abstract Photosynthetic acclimation to elevated atmospheric CO2 concentration ([CO2]) accompanies decreased leaf nitrogen (N) content. Elevated air temperatures may enhance crop N nutrient content. Whether enhanced leaf N content at high temperatures relieves photosynthetic acclimation to high [CO2] in rice is unclear, so we investigated the effects of elevated [CO2] (eC; ambient [CO2]+200 μmol mol−1 CO2 and ambient temperature), elevated air temperature (eT; ambient+1 °C), and elevated temperature and [CO2] together (eT + eC; ambient+1 °C +200 μmol mol−1 CO2) compared to ambient [CO2] and temperature (Ambient) on photosynthetic and physiological parameters, biomass, and N accumulation and distribution throughout rice grain filling stages in 2015 and 2016. Net leaf photosynthesis (Pn) increased under eC, but the magnitude of Pn increase decreased as grain filling progressed, which was exacerbated under eT + eC. The total leaf N (TLN) content decreased by 7.1 % and increased by 4.7 % on average during the whole grain filling stage under eC and eT compared with Ambient, respectively. However, increasing TLN under elevated temperature did not offset the TLN reduction under [CO2] enrichment, similar to the effects of elevated [CO2] and air temperature on chlorophyll (Chl) and carotenoid (Caro) content. The percentage decrease in Rubisco content was larger under individual changes or the combined elevation of [CO2] and air temperature than the percentage change in TLN under eC. Meanwhile, the maximum rate of Rubisco carboxylation at 25 °C (Vcmax25) and the maximum rate of electron transport driving RuBP regeneration at 25 °C (Jmax25) declined significantly under eT + eC. Vcmax25 had a positive relationship with Rubisco content, and Jmax25 had a positive relationship with Chl and Caro content. At the crop level, eC enhanced biomass but reduced N distribution in leaves. Furthermore, the decrease in biomass had a greater effect than the increase in TLN under eT, reducing N distribution in leaves. Photosynthetic acclimation was mainly due to the reduction in TLN and crop N distribution and the increased reduction in leaf N distribution to Rubisco under eT + eC. Therefore, an air temperature increase of approximately 1 °C exacerbated photosynthetic acclimation under eC. These results further elucidated the photosynthesis responses in rice to future climate conditions.

Differential Flag Leaf and Ear Photosynthetic Performance Under Elevated (CO2) Conditions During Grain Filling Period in Durum Wheat.

Elevated concentrations of CO2 (CO2) in plants with C3 photosynthesis metabolism, such as wheat, stimulate photosynthetic rates. However, photosynthesis tends to decrease as a function of exposure to high (CO2) due to down-regulation of the photosynthetic machinery, and this phenomenon is defined as photosynthetic acclimation. Considerable efforts are currently done to determine the effect of photosynthetic tissues, such us spike, in grain filling. There is good evidence that the contribution of ears to grain filling may be important not only under good agronomic conditions but also under high (CO2). The main objective of this study was to compare photoassimilate production and energy metabolism between flag leaves and glumes as part of ears of wheat (Triticum turgidum L. subsp. durum cv. Amilcar) plants exposed to ambient [a(CO2)] and elevated [e(CO2)] (CO2) (400 and 700 μmol mol–1, respectively). Elevated CO2 had a differential effect on the responses of flag leaves and ears. The ears showed higher gross photosynthesis and respiration rates compared to the flag leaves. The higher ear carbohydrate content and respiration rates contribute to increase the grain dry mass. Our results support the concept that acclimation of photosynthesis to e(CO2) is driven by sugar accumulation, reduction in N concentrations and repression of genes related to photosynthesis, glycolysis and the tricarboxylic acid cycle, and that these were more marked in glumes than leaves. Further, important differences are described on responsiveness of flag leaves and ears to e(CO2) on genes linked with carbon and nitrogen metabolism. These findings provide information about the impact of e(CO2) on ear development during the grain filling stage and are significant for understanding the effects of increasing (CO2) on crop yield.

Triose phosphate utilization limitation: an unnecessary complexity in terrestrial biosphere model representation of photosynthesis

Triose phosphates are the principal product of photosynthesis. They are used within the chloroplast for starch synthesis, or translocated to the cytosol where they are used to fuel sucrose synthesis. Use of triose phosphate releases inorganic phosphate, and is under strict metabolic control that matches the supply of triose phosphate from the Calvin-Benson cycle to the demand for carbon by sinks (Heldt & Heldt, 2011; McClain & Sharkey, 2019). However, a low rate of triose phosphate utilization (TPU) can deplete the phosphate pool, restrict ATP synthesis and reduce the availability of ATP to power the Calvin-Benson cycle, thereby limiting photosynthesis (Sharkey, 1985).

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 (qL) 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.

Mechanisms underlying photosynthetic acclimation to high temperature are different between Vitis vinifera cv. Syrah and Grenache

Photosynthesis acclimation to high temperature differs among and within species. Grapevine intra-specific variation in photosynthetic acclimation to elevated temperature has been scarcely assessed. Our objectives were to (i) evaluate the mechanisms underlying long-term acclimation of photosynthesis to elevated temperature in grapevine, and (ii) determine whether these responses are similar among two varieties. A warming experiment with well irrigated Grenache and Syrah field-grown plants was performed during two growing seasons comparing plants exposed at ambient temperature (control) with plants in open-top chambers (heating) that increased mean air temperature between 1.5 and 3.6°C. Photosynthetic acclimation was assessed through the response of net assimilation (An), Rubisco carboxylation rate (Vcmax) and electron transport rate (Jmax), at leaf temperatures from 20 to 40°C. Our results evidenced different mechanisms for photosynthetic acclimation to elevated temperature. Compared with control, Grenache heated increased An, maintaining higher Vcmax and Jmax at temperatures above 35°C. By contrast, Syrah heated and control presented similar values of An, Vcmax and Jmax, evidencing an adjustment of photosynthesis without increasing C assimilation. Both varieties increased the optimum temperature for An, but to a lesser extent when growth temperature was higher. Our study provides evidence that grapevine varieties present different acclimation mechanisms to expected warming.

Developmental acclimation of the thylakoid proteome to light intensity in Arabidopsis.

Photosynthetic acclimation, the ability to adjust the composition of the thylakoid membrane to optimise the efficiency of electron transfer to the prevailing light conditions, is crucial to plant fitness in the field. While much is known about photosynthetic acclimation in Arabidopsis, to date there has been no study that combines both quantitative label-free proteomics and photosynthetic analysis by gas exchange, chlorophyll fluorescence and P700 absorption spectroscopy. Using these methods we investigated how the levels of 402 thylakoid proteins, including many regulatory proteins not previously quantified, varied upon long-term (weeks) acclimation of Arabidopsis to low (LL), moderate (ML) and high (HL) growth light intensity and correlated these with key photosynthetic parameters. We show that changes in the relative abundance of cytb6 f, ATP synthase, FNR2, TIC62 and PGR6 positively correlate with changes in estimated PSII electron transfer rate and CO2 assimilation. Improved photosynthetic capacity in HL grown plants is paralleled by increased cyclic electron transport, which positively correlated with NDH, PGRL1, FNR1, FNR2 and TIC62, although not PGR5 abundance. The photoprotective acclimation strategy was also contrasting, with LL plants favouring slowly reversible non-photochemical quenching (qI), which positively correlated with LCNP, while HL plants favoured rapidly reversible quenching (qE), which positively correlated with PSBS. The long-term adjustment of thylakoid membrane grana diameter positively correlated with LHCII levels, while grana stacking negatively correlated with CURT1 and RIQ protein abundance. The data provide insights into how Arabidopsis tunes photosynthetic electron transfer and its regulation during developmental acclimation to light intensity.

Identification and Characterization of the Heat-Induced Plastidial Stress Granules Reveal New Insight Into Arabidopsis Stress Response.

Plants exhibit different physiological and molecular responses to adverse changes in their environment. One such molecular response is the sequestration of proteins, RNAs, and metabolites into cytoplasmic bodies called stress granules (cSGs). Here we report that, in addition to cSGs, heat stress also induces the formation of SG-like foci (cGs) in the chloroplasts of the model plant Arabidopsis thaliana. Similarly to the cSGs, (i) cpSG assemble rapidly in response to stress and disappear when the stress ceases, (ii) cpSG formation is inhibited by treatment with a translation inhibitor (lincomycin), and (iii) cpSG are composed of a stable core and a fluid outer shell. A previously published protocol for cSG extraction was successfully adapted to isolate cpSG, followed by protein, metabolite, and RNA analysis. Analogously to the cSGs, cpSG sequester proteins essential for SG formation, dynamics, and function, also including RNA-binding proteins with prion-like domain, ATPases and chaperones, and the amino acids proline and glutamic acid. However, the most intriguing observation relates to the cpSG localization of proteins, such as a complete magnesium chelatase complex, which is involved in photosynthetic acclimation to stress. These data suggest that cpSG have a role in plant stress tolerance.

Metabolic flux from the chloroplast provides signals controlling photosynthetic acclimation to cold in Arabidopsis thaliana.

Photosynthesis is especially sensitive to environmental conditions, and the composition of the photosynthetic apparatus can be modulated in response to environmental change, a process termed photosynthetic acclimation. Previously, we identified a role for a cytosolic fumarase, FUM2 in acclimation to low temperature in Arabidopsis thaliana. Mutant lines lacking FUM2 were unable to acclimate their photosynthetic apparatus to cold. Here, using gas exchange measurements and metabolite assays of acclimating and non-acclimating plants, we show that acclimation to low temperature results in a change in the distribution of photosynthetically fixed carbon to different storage pools during the day. Proteomic analysis of wild-type Col-0 Arabidopsis and of a fum2 mutant, which was unable to acclimate to cold, indicates that extensive changes occurring in response to cold are affected in the mutant. Metabolic and proteomic data were used to parameterize metabolic models. Using an approach called flux sampling, we show how the relative export of triose phosphate and 3-phosphoglycerate provides a signal of the chloroplast redox state that could underlie photosynthetic acclimation to cold.