Showing papers on "Photoinhibition published in 2007"
TL;DR: It is postulate that most types of environmental stress inhibit the fixation of CO(2) with the resultant generation of ROS, which, in turn, inhibit protein synthesis, which is required for the repair of PSII.
1,245 citations
TL;DR: Different differences between water deficit and salinity were revealed and water-deficit-treated plants appear to have a higher demand than salinized plants to adjust osmotically, detoxify free radicals (reactive oxygen species), and cope with photoinhibition.
Abstract: Grapes are grown in semiarid environments, where drought and salinity are common problems. Microarray transcript profiling, quantitative reverse transcription-PCR, and metabolite profiling were used to define genes and metabolic pathways in Vitis vinifera cv. Cabernet Sauvignon with shared and divergent responses to a gradually applied and long-term (16 days) water-deficit stress and equivalent salinity stress. In this first-of-a-kind study, distinct differences between water deficit and salinity were revealed. Water deficit caused more rapid and greater inhibition of shoot growth than did salinity at equivalent stem water potentials. One of the earliest responses to water deficit was an increase in the transcript abundance of RuBisCo activase (day 4), but this increase occurred much later in salt-stressed plants (day 12). As water deficit progressed, a greater number of affected transcripts were involved in metabolism, transport, and the biogenesis of cellular components than did salinity. Salinity affected a higher percentage of transcripts involved in transcription, protein synthesis, and protein fate than did water deficit. Metabolite profiling revealed that there were higher concentrations of glucose, malate, and proline in water-deficit-treated plants as compared to salinized plants. The metabolite differences were linked to differences in transcript abundance of many genes involved in energy metabolism and nitrogen assimilation, particularly photosynthesis, gluconeogenesis, and photorespiration. Water-deficit-treated plants appear to have a higher demand than salinized plants to adjust osmotically, detoxify free radicals (reactive oxygen species), and cope with photoinhibition.
541 citations
TL;DR: It is proposed that the NDH-dependent cyclic pathway around PSI participates to the ATP supply in conditions of high ATP demand and together with PTOX regulates cyclic electron transfer activity by tuning the redox state of intersystem electron carriers.
Abstract: Besides major photosynthetic complexes of oxygenic photosynthesis, new electron carriers have been identified in thylakoid membranes of higher plant chloroplasts. These minor components, located in the stroma lamellae, include a plastidial NAD(P)H dehydrogenase (NDH) complex and a plastid terminal plastoquinone oxidase (PTOX). The NDH complex, by reducing plastoquinones (PQs), participates in one of the two electron transfer pathways operating around photosystem I (PSI), the other likely involving a still uncharacterized ferredoxin-plastoquinone reductase (FQR) and the newly discovered PGR5. The existence of a complex network of mechanisms regulating expression and activity of the NDH complex, and the presence of higher amounts of NDH complex and PTOX in response to environmental stress conditions the phenotype of mutants, indicate that these components likely play a role in the acclimation of photosynthesis to changing environmental conditions. Based on recently published data, we propose that the NDH-dependent cyclic pathway around PSI participates to the ATP supply in conditions of high ATP demand (such as high temperature or water limitation) and together with PTOX regulates cyclic electron transfer activity by tuning the redox state of intersystem electron carriers. In response to severe stress conditions, PTOX associated to the NDH and/or the PGR5 pathway may also limit electron pressure on PSI acceptor and prevent PSI photoinhibition.
387 citations
TL;DR: RNAi technology was applied to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat and increase photosynthetic efficiencies under high-light conditions, resulting in an increased efficiency of cell cultivation under elevated light conditions.
Abstract: The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical 'fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H-2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII.
331 citations
TL;DR: Photosystem I light harvesting function was shown to be regulated through different mechanisms like the control of photosystem I to photosystem II ratio and the association or dissociation of Lhcb polypeptides to photoystem I.
290 citations
TL;DR: Estuarine species show a higher and more flexible capacity for photoprotection than oceanic and coastal species, and when exposed to excess light, the impairment of their photosynthetic capacity because of photoinhibition was reduced, resulting in maintenance of growth in a fluctuating light regime.
Abstract: In this study, we show a fundamental difference between diatom species from different marine habitats in their ability to cope with changes in irradiance. Estuarine species show a higher and more flexible capacity for photoprotection than oceanic and coastal species, and when exposed to excess light, the impairment of their photosynthetic capacity because of photoinhibition was reduced. This resulted in maintenance of growth in a fluctuating light regime, conferring the estuarine species an adaptive advantage. The ability of diatoms, and to a larger extent other phytoplankton, to occupy a wide range of ecological niches depends critically on their capacity to exploit the differences in underwater light climate. These results might explain how diatoms adapt to the challenge of maintaining optimal photosynthetic production in turbulent waters, in which the rate of light change is high.
228 citations
TL;DR: It is concluded that the drought-induced inhibition of photosynthesis under different irradiances in the rice was due to both diffusive and metabolic limitations.
Abstract: Photoprotection mechanisms of rice plants were studied when its seedlings were subjected to the combined stress of water and high light. The imposition of water stress, induced by PEG 6000 which was applied to roots, resulted in substantial inhibition of stomatal conductance and net photosynthesis under all irradiance treatments. Under high light stress, the rapid decline of photosynthesis with the development of water stress was accompanied by decreases in the maximum velocity of RuBP carboxylation by Rubisco (V(cmax)), the capacity for ribulose-1,5-bisphosphate regeneration (J(max)), Rubisco and stromal FBPase activities, and the quantum efficiency of photosystem II, in the absence of any stomatal limitation of CO(2) supply. Water stress significantly reduced the energy flux via linear electron transport (J(PSII)), but increased light-dependent and DeltapH- and xanthophyll-mediated thermal dissipation (J(NPQ)). It is concluded that the drought-induced inhibition of photosynthesis under different irradiances in the rice was due to both diffusive and metabolic limitations. Metabolic limitation of photosynthesis may be related to the adverse effects of some metabolic processes and the oxidative damage to the chloroplast. Meanwhile, an enhanced thermal dissipation is an important process to minimize the adverse effects of drought and high irradiance when CO(2) assimilation is suppressed.
223 citations
TL;DR: Results suggest that Deg1 cooperates with the stroma-exposed proteases FtsH and Deg2 in degrading D1 protein during repair from photoinhibition by cleaving lumen-exp exposed regions of the protein.
Abstract: Deg1 is a Ser protease peripherally attached to the lumenal side of the thylakoid membrane. Its physiological function is unknown, but its localization makes it a suitable candidate for participation in photoinhibition repair by degradation of the photosystem II reaction center protein D1. We transformed Arabidopsis thaliana with an RNA interference construct and obtained plants with reduced levels of Deg1. These plants were smaller than wild-type plants, flowered earlier, were more sensitive to photoinhibition, and accumulated more of the D1 protein, probably in an inactive form. Two C-terminal degradation products of the D1 protein, of 16 and 5.2 kD, accumulated at lower levels compared with the wild type. Moreover, addition of recombinant Deg1 to inside-out thylakoid membranes isolated from the mutant could induce the formation of the 5.2-kD D1 C-terminal fragment, whereas the unrelated proteases trypsin and thermolysin could not. Immunoblot analysis revealed that mutants containing less Deg1 also contain less FtsH protease, and FtsH mutants contain less Deg1. These results suggest that Deg1 cooperates with the stroma-exposed proteases FtsH and Deg2 in degrading D1 protein during repair from photoinhibition by cleaving lumen-exposed regions of the protein. In addition, they suggest that accumulation of Deg1 and FtsH proteases may be coordinated.
210 citations
TL;DR: The results suggest that the increased thermotolerance induced by accumulation of glycinebetaine in vivo was associated with the enhancement of the repair of PSII from heat-enhanced photo inhibition, which might be due to less accumulation of reactive oxygen species in transgenic plants.
Abstract: Genetically engineered tobacco (Nicotiana tabacum L.) with the ability to accumulate glycinebetaine was established. The wild type and transgenic plants were exposed to heat treatment (25-50 degrees C) for 4 h in the dark and under growth light intensity (300 mumol m(-2) s(-1)). The analyses of oxygen-evolving activity and chlorophyll fluorescence demonstrated that photosystem II (PSII) in transgenic plants showed higher thermotolerance than in wild type plants in particular when heat stress was performed in the light, suggesting that the accumulation of glycinebetaine leads to increased tolerance to heat-enhanced photoinhibition. This increased tolerance was associated with an improvement on thermostability of the oxygen-evolving complex and the reaction center of PSII. The enhanced tolerance was caused by acceleration of the repair of PSII from heat-enhanced photoinhibition. Under heat stress, there was a significant accumulation of H(2)O(2), O (2) (-) and catalytic Fe in wild type plants but this accumulation was much less in transgenic plants. Heat stress significantly decreased the activities of catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase in wild type plants whereas the activities of these enzymes either decreased much less or maintained or even increased in transgenic plants. In addition, heat stress increased the activity of superoxide dismutase in wild type plants but this increase was much greater in transgenic plants. Furthermore, transgenic plants also showed higher content of ascorbate and reduced glutathione than that of wild type plants under heat stress. The results suggest that the increased thermotolerance induced by accumulation of glycinebetaine in vivo was associated with the enhancement of the repair of PSII from heat-enhanced photo inhibition, which might be due to less accumulation of reactive oxygen species in transgenic plants.
185 citations
TL;DR: The results suggest that the photorespiratory pathway helps avoid inhibition of the synthesis of the D1 protein, which is important for the repair of photodamaged PSII upon interruption of the Calvin cycle.
Abstract: Oxygenation of ribulose-1,5-bisphosphate catalyzed by Rubisco produces glycolate-2-P. The photorespiratory pathway, which consists of photorespiratory carbon and nitrogen cycles, metabolizes glycolate-2-P to the Calvin cycle intermediate glycerate-3-P and is proposed to be important for avoiding photoinhibition of photosystem II (PSII), especially in C3 plants. We show here that mutants of Arabidopsis (Arabidopsis thaliana) with impairment of ferredoxin-dependent glutamate synthase, serine hydroxymethyltransferase, glutamate/malate transporter, and glycerate kinase had accelerated photoinhibition of PSII by suppression of the repair of photodamaged PSII and not acceleration of the photodamage to PSII. We found that suppression of the repair process was attributable to inhibition of the synthesis of the D1 protein at the level of translation. Our results suggest that the photorespiratory pathway helps avoid inhibition of the synthesis of the D1 protein, which is important for the repair of photodamaged PSII upon interruption of the Calvin cycle.
183 citations
TL;DR: The results suggest that DEG5 and DEG8 have a synergistic function in the primary cleavage of the CD loop of the PSII reaction center protein D1.
Abstract: The widely distributed DEGP proteases play important roles in the degradation of damaged and misfolded proteins. Arabidopsis thaliana contains 16 DEGP-like proteases, four of which are located in the chloroplast. Here, we show that DEG5 and DEG8 form a hexamer in the thylakoid lumen and that recombinant DEG8 is proteolytically active toward both a model substrate (β-casein) and photodamaged D1 protein of photosystem II (PSII), producing 16-kD N-terminal and 18-kD C-terminal fragments. Inactivation of DEG5 and DEG8 resulted in increased sensitivity to photoinhibition. Turnover of newly synthesized D1 protein in the deg5 deg8 double mutant was impaired, and the degradation of D1 in the presence of the chloroplast protein synthesis inhibitor lincomycin under high-light treatment was slowed in the mutants. Thus, DEG5 and DEG8 are important for efficient turnover of the D1 protein and for protection against photoinhibition in vivo. The deg5 deg8 double mutant showed increased photosensitivity and reduced rates of D1 degradation compared with single mutants of deg5 and deg8. A 16-kD N-terminal degradation fragment of the D1 protein was detected in wild-type plants but not in the deg5 deg8 mutant following in vivo photoinhibition. Therefore, our results suggest that DEG5 and DEG8 have a synergistic function in the primary cleavage of the CD loop of the PSII reaction center protein D1.
TL;DR: It is suggested that the protein/lipid interface is the active site for the antioxidant activity of zeaxanthin, which mediates stress tolerance by the protection of bound lipids in transformed plants.
TL;DR: It is concluded that neoxanthin preserves PSII from photoinactivation and protects membrane lipids from photooxidation by reactive oxygen species.
Abstract: The aba4-1 mutant completely lacks neoxanthin but retains all other xanthophyll species. The missing neoxanthin in light-harvesting complex (Lhc) proteins is compensated for by higher levels of violaxanthin, albeit with lower capacity for photoprotection compared with proteins with wild-type levels of neoxanthin. Detached leaves of aba4-1 were more sensitive to oxidative stress than the wild type when exposed to high light and incubated in a solution of photosensitizer agents. Both treatments caused more rapid pigment bleaching and lipid oxidation in aba4-1 than wild-type plants, suggesting that neoxanthin acts as an antioxidant within the photosystem II (PSII) supercomplex in thylakoids. While neoxanthin-depleted Lhc proteins and leaves had similar sensitivity as the wild type to hydrogen peroxide and singlet oxygen, they were more sensitive to superoxide anions. aba4-1 intact plants were not more sensitive than the wild type to high-light stress, indicating the existence of compensatory mechanisms of photoprotection involving the accumulation of zeaxanthin. However, the aba4-1 npq1 double mutant, lacking zeaxanthin and neoxanthin, underwent stronger PSII photoinhibition and more extensive oxidation of pigments than the npq1 mutant, which still contains neoxanthin. We conclude that neoxanthin preserves PSII from photoinactivation and protects membrane lipids from photooxidation by reactive oxygen species. Neoxanthin appears particularly active against superoxide anions produced by the Mehler's reaction, whose rate is known to be enhanced in abiotic stress conditions.
TL;DR: In this article, an 8-year-old olive (Olea europaea L., cv. Cobrancosa) commercial orchard located in northeast Portugal was subjected to a rainfed control (T0) and three treatments (T1, T2, T3) that received a seasonal water amount equivalent to 30, 60% and 100% of the estimated local evaporative demand by a drip irrigation system.
Abstract: Irrigation effects were investigated on an 8-year-old olive (Olea europaea L., cv. Cobrancosa) commercial orchard located in northeast Portugal. Trees were subjected to a rainfed control (T0) and three treatments (T1, T2, T3) that received a seasonal water amount equivalent to 30%, 60% and 100% of the estimated local evaporative demand by a drip irrigation system. Irrigation increases the photosynthetic activity of olive trees, in association with increases in water status, and reduces the midday and afternoon depression in gas exchange. The closely association between photosynthetic rate (A) and stomatal conductance (gs) revealed that the decline in net photosynthesis over the course of the day was largely a consequence of stomatal limitation. However, the ratio of intercellular to atmospheric CO2 concentration increased markedly from morning to midday in non-irrigated plants, in spite of lower gs, suggesting that non-stomatal limitations of photosynthesis also occur when environmental conditions become more stressful. The occurrence of perturbations at chloroplastic level in rainfed plants was demonstrated by a lower maximum photochemical efficiency of photosystem II during the afternoon. Chlorophyll fluorescence measurements also revealed the occurrence of a dynamic photoinhibition in irrigated trees, mainly in T2 and T3, which seemed to be effective in protecting the photosynthetic apparatus from photodamage. Irrigation enhances antioxidant protection and decreases the oxidative damage at leaf level. Leaves grown under rainfed conditions revealed symptoms of oxidative stress, like the reduction (14%) in chlorophyll concentration and the increased levels (57%) of lipid peroxidation. We also found that the scavenging function of superoxide dismutase was impaired in rainfed plants. In contrast, the low thiobarbituric acid reactive substances concentration in T3 indicates that irrigation enhances the repairing mechanisms and decreases the oxidative damage by lipid peroxidation. Accordingly, leaves in T3 treatment had high levels of –SH compounds and the highest antioxidant potential. Meanwhile, the finding that guaiacol peroxidase activity increased in rainfed plants, associated with the appearance of oxidative damage, suggests that this enzyme has no major antioxidative function in olive.
TL;DR: In depth analysis of the mutant phenotypes suggests that α-br branch (lutein) and β-branch (zeaxanthin, violaxanth in, and neoxanthin) xanthophylls have distinct and complementary roles in antenna protein assembly and in the mechanisms of photoprotection.
TL;DR: Evidence is provided that singlet oxygen stimulates GPXH expression by activating a signaling mechanism outside the thylakoid membrane, indicating that single oxygen can stimulate a response farther from its production site than generally believed.
TL;DR: The differences in repair rate correspond to the light and nutrient conditions that characterize the site of origin of the Prochlorococcus and Synechococcus isolates, and determine the upward fluctuation in irradiance they can tolerate, indicating that photoinhibition due to transient high-light exposure influences their distribution in the ocean.
Abstract: Prochlorococcus and Synechococcus picocyanobacteria are dominant contributors to marine primary production over large areas of the ocean. Phytoplankton cells are entrained in the water column and are thus often exposed to rapid changes in irradiance within the upper mixed layer of the ocean. An upward fluctuation in irradiance can result in photosystem II photoinactivation exceeding counteracting repair rates through protein turnover, thereby leading to net photoinhibition of primary productivity, and potentially cell death. Here we show that the effective cross-section for photosystem II photoinactivation is conserved across the picocyanobacteria, but that their photosystem II repair capacity and protein-specific photosystem II light capture are negatively correlated and vary widely across the strains. The differences in repair rate correspond to the light and nutrient conditions that characterize the site of origin of the Prochlorococcus and Synechococcus isolates, and determine the upward fluctuation in irradiance they can tolerate, indicating that photoinhibition due to transient high-light exposure influences their distribution in the ocean.
TL;DR: The light-dependent multiple and differential phosphorylation of CP29 linker protein in the green algae is suggested to control photosynthetic state transitions and uncoupling of light harvesting proteins from photosystem II under high light.
TL;DR: In this article, cells of a calcifying strain of Emiliania huxleyi were grown at three irradiances (30, 300, and 800 mmol photons m22 s21) in combination with four calcium (Ca) concentrations (0.1, 1, 2.5, and 10 mmol L21) leading to different degrees of calcification in the same strain.
Abstract: Various protective and metabolic functions for coccolithophore calcification have been proposed such as providing a means to supply CO2 for photosynthesis. It has also been speculated that calcification helps to dissipate excess energy under high irradiance, thereby circumventing photoinhibition. To address these questions, cells of a calcifying strain of Emiliania huxleyi were grown at three irradiances (30, 300, and 800 mmol photons m22 s21) in combination with four calcium (Ca) concentrations (0.1, 1, 2.5, and 10 mmol L21) leading to different degrees of calcification in the same strain. Growth rates (m), particulate organic carbon (POC), and inorganic carbon (PIC) production as well as carbon isotope fractionation (ep) were determined. Photosynthetic O2 evolution and CO2 and HCO { uptake rates were measured by membrane inlet mass spectrometry (MIMS). The application of this multimethod approach provides new information on the role of calcification in E. huxleyi. Noncalcifying cells showed POC production rates as high as calcifying ones. No differences in ep were observed under different Ca concentrations. MIMS measurements indicate that noncalcifying cells can photosynthesize as efficiently as, or even more efficiently than, calcifying ones and that both use HCO { as the main carbon source. The ratio of photosynthetic HCO { uptake relative to net fixation did not differ among cells acclimated to 10 mmol L21 or to 0.1 mmol L21 Ca. These results indicate that (1) calcification is not involved in photosynthetic carbon acquisition, and (2) calcification does not provide a means of energy dissipation under high irradiances.
TL;DR: This is the first study to investigate the sub-lethal effects of chronic herbicide-induced photoinhibition on symbiotic corals and provides evidence of a link between reduced energy acquisition due to PSII photoin inhibition and reduced reproductive output in zooxanthellate corals.
Abstract: The photosystem II (PSII) herbicide diuron is commonly used within catchments that drain into the Great Barrier Reef lagoon, where it potentially reduces photosynthesis in Symbiodinium, the dinoflagellate symbiont associated with reef corals. Here we examine the importance of energy (carbohydrates) derived from photosynthesis to the gametogenesis of corals following long-term, experimental exposures to diuron. Two broadcast spawning corals, Acropora tenuis and A. valida, and a brooding coral, Pocillopora damicornis, were exposed to 0 (controls), 1.0 (low) and 10 (moderate) µg l–1 diuron treatments for 2 to 3 mo prior to spawning or planulation. Diuron caused photoinhibition in each species, with pulse amplitude modulation (PAM) fluorometery recording consistent declines in effective quantum yields of 20% at 1.0 µg l–1 and 75% at 10 µg l–1 diuron compared to control corals. A. valida and P. damicornis were both sensitive to chronic diuron-induced photoinhibition, becoming severely bleached (loss of Symbiodinium spp. and/or reductions in light-harvesting pigments), especially at 10 µg l–1 diuron. At this moderate concentration, A. valida sustained both partial and full colony mortality. A. tenuis was more resistant to these concentrations of diuron, and neither bleached nor sustained partial mortality in any of the treatments. We found 2.5- to 5-fold reductions in total lipid content (coral tissue, oocytes and planulae) for the 3 species in the presence of diuron, indicating significant use of storage lipid to meet nutritional demands under conditions of chronic photoinhibition. Polyp fecundity was reduced by 6-fold in A. valida and both A. valida and P. damicornis were unable to spawn or planulate following long-term exposures to 10 µg l–1 diuron. This is the first study to investigate the sub-lethal effects of chronic herbicide-induced photoinhibition on symbiotic corals and provides evidence of a link between reduced energy acquisition due to PSII photoinhibition and reduced reproductive output in zooxanthellate corals.
TL;DR: The results suggest that salt stress enhanced photoinhibition by inhibiting repair of PSII and that the katE transgene increased the resistance of the chloroplast's translational machinery to salt stress by scavenging hydrogen peroxide.
Abstract: During photoinhibition of photosystem II (PSII) in cyanobacteria, salt stress inhibits the repair of photodamaged PSII and, in particular, the synthesis of the D1 protein (D1). We investigated the effects of salt stress on the repair of PSII and the synthesis of D1 in wild-type tobacco ( Nicotiana tabacum ‘Xanthi’) and in transformed plants that harbored the katE gene for catalase from Escherichia coli . Salt stress due to NaCl enhanced the photoinhibition of PSII in leaf discs from both wild-type and katE- transformed plants, but the effect of salt stress was less significant in the transformed plants than in wild-type plants. In the presence of lincomycin, which inhibits protein synthesis in chloroplasts, the activity of PSII decreased rapidly and at similar rates in both types of leaf disc during photoinhibition, and the observation suggests that repair of PSII was protected by the transgene-coded enzyme. Incorporation of [ 35 S]methionine into D1 during photoinhibition was inhibited by salt stress, and the transformation mitigated this inhibitory effect. Northern blotting revealed that the level of psbA transcripts was not significantly affected by salt stress or by the transformation. Our results suggest that salt stress enhanced photoinhibition by inhibiting repair of PSII and that the katE transgene increased the resistance of the chloroplast9s translational machinery to salt stress by scavenging hydrogen peroxide.
TL;DR: A hypothetical scheme for the cyanobacterial photosynthesis is proposed that moderate heat stress inhibits the translation machinery and glycinebetaine protects it against the heat-induced inactivation of photosystem II.
TL;DR: In this article, a proteome analysis of Arabidopsis thaliana thylakoid-associated polysome nascent chain complexes was performed to find novel proteins involved in the biogenesis, maintenance and turnover of PSII.
Abstract: A proteome analysis of Arabidopsis thaliana thylakoid-associated polysome nascent chain complexes was performed to find novel proteins involved in the biogenesis, maintenance and turnover of thylakoid protein complexes, in particular the PSII (photosystem II) complex, which exhibits a high turnover rate. Four unknown proteins were identified, of which TLP18.3 (thylakoid lumen protein of 18.3 kDa) was selected for further analysis. The Arabidopsis mutants (SALK_109618 and GABI-Kat 459D12) lacking the TLP18.3 protein showed higher susceptibility of PSII to photoinhibition. The increased susceptibility of ΔTLP18.3 plants to high light probably originates from an inefficient reassembly of PSII monomers into dimers in the grana stacks, as well as from an impaired turnover of the D1 protein in stroma exposed thylakoids. Such dual function of the TLP18.3 protein is in accordance with its even distribution between the grana and stroma thylakoids. Notably, the lack of the TLP18.3 protein does not lead to a severe collapse of the PSII complexes, suggesting a redundancy of proteins assisting these particular repair steps to assure functional PSII. The ΔTLP18.3 plants showed no clear visual phenotype under standard growth conditions, but when challenged by fluctuating light during growth, the retarded growth of ΔTLP18.3 plants was evident.
TL;DR: Prolonged exposure to UV radiation at the nonstressful temperature of 27 °C conferred protection against independent, thermally induced photoinhibition in all four species.
Abstract: Experiments were performed on coral species containing clade A (Stylophora pistillata, Montipora aequi- tuberculata) or clade C (Acropora sp., Pavona cactus) zooxanthellae. The photosynthetic efficiency (Fv/Fm )o f the corals was first assessed during a short-term increase in temperature (from 27 °C to 29 °C, 32 °C, and 34 °C) and acute exposure to UV radiation (20.5 W m 2 UVA and 1.2 Wm 2 UVB) alone or in combination. Increasing temper- ature to 34 °C significantly decreased the Fv/Fm in S. pistillata and M. aequituberculata. Increased UV radiation alone significantly decreased the Fv/Fm of all coral species, even at 27 °C. There was a combined effect of temperature and UV radiation, which reduced Fv/Fm in all corals by 25% to 40%. During a long-term exposure to UV radiation (17 days) the Fv /Fm was significantly reduced after 3 days' exposure in all species, which did not recover their initial values, even after 17 days. By this time, all corals had synthesized mycosporine-like amino acids (MAAs). The concentration and diversity of MAAs differed among spe- cies, being higher for corals containing clade A zooxanthel- lae. Prolonged exposure to UV radiation at the nonstressful temperature of 27 °C conferred protection against indepen- dent, thermally induced photoinhibition in all four species.
TL;DR: The results highlight the interspecific variability of gross photosynthesis in the stem and its correlation with structural traits like those found for leaves and suggest that the selection of photosynthetic traits has operated under similar constraints in stems and leaves.
Abstract: The photosynthetic characteristics of current-year stems of six deciduous tree species, two evergreen tree species and ginkgo (Ginkgo biloba L.) were compared. Gas exchange, chlorophyll concentration, nitrogen concentration and maximum quantum yield of PSII were measured in stems in summer and winter. A light-induced decrease in stem CO(2) efflux was observed in all species. The apparent gross photosynthetic rate in saturating light ranged from 0.72 micromol m(-2 )s(-1) (ginkgo, in winter) to 3.73 micromol m(-2) s(-1) (Alnus glutinosa (L.) Gaertn., in summer). Despite this variability, a unique correlation (slope = 0.75), based on our results and those reported in the literature, was found between gross photosynthetic rate and dark respiration rate. Mass-based gross photosynthetic rate decreased with stem mass per area and correlated to chlorophyll concentration and nitrogen concentration, both in summer and winter. The radial distribution of stem chlorophyll differed among species, but all species except ginkgo had chlorophyll as deep as the pith. In summer, the maximum quantum yield of stem PSII (estimated from the ratio of variable to maximal fluorescence; F (v)/F (m)) of all species was near the optimal value found for leaves. By contrast, the values were highly variable in winter, suggesting large differences in sensitivity to low-temperature photoinhibition. The winter values of Fv/Fm were only 31-60% of summer values for the deciduous species, whereas the evergreen conifer species maintained high F (v)/F (m) in winter. The results highlight the interspecific variability of gross photosynthesis in the stem and its correlation with structural traits like those found for leaves. The structural correlations suggest that the selection of photosynthetic traits has operated under similar constraints in stems and leaves.
TL;DR: Results indicate that overexpression of LeGPAT increased the levels of PG cis-unsaturated fatty acids in thylakoid membrane, which was beneficial for the recovery of chilling-induced PS I photoinhibition in tomato.
Abstract: A tomato (Lycopersicon esculentum Mill.) glycerol-3-phosphate acyltransferase gene (LeGPAT) was isolated. The deduced amino acid sequence revealed that LeGPAT contained four acyltransferase domains, showing high identities with GPAT in other plant species. A GFP fusion protein of LeGPAT was targeted to chloroplast in cowpea mesophyll protoplast. RNA gel blot showed that the mRNA accumulation of LeGPAT in the wild type (WT) was induced by chilling temperature. Higher expression levels were observed when tomato leaves were exposed to 4°C for 4 h. RNA gel and western blot analysis confirmed that the sense gene LeGPAT was transferred into the tomato genome and overexpressed under the control of 35S-CaMV. Although tomato is classified as a chilling-sensitive plant, LeGPAT exhibited selectivity to 18:1 over 16:0. Overexpression of LeGPAT increased total activity of LeGPAT and cis-unsaturated fatty acids in PG in thylakoid membrane. Chilling treatment induced less ion leakage from the transgenic plants than from the WT. The photosynthetic rate and the maximal photochemical efficiency of PS II (Fv/Fm) in transgenic plants decreased more slowly during chilling stress and recovered faster than in WT under optimal conditions. The oxidizable P700 in both WT and transgenic plants decreased obviously at chilling temperature under low irradiance, but the oxidizable P700 recovered faster in transgenic plants than in the WT. These results indicate that overexpression of LeGPAT increased the levels of PG cis-unsaturated fatty acids in thylakoid membrane, which was beneficial for the recovery of chilling-induced PS I photoinhibition in tomato.
TL;DR: It is proposed that the successful growth leading to the proliferation of these two differently pigmented strains may largely depend on the combined conditions of light and temperature, and could be considered as two ecotypes that are adapted to different light andTemperature environments.
Abstract: The effects of temperature, light intensity, and quality on the growth of the cyanobacteria Planktothrix agardhii (Gomont) Anag. et Komarek and P. rubescens (Gomont) Anag. et Komarek were assessed in batch cultures. The relative competitiveness of the green-pigmented P. agardhii and the red-pigmented P. rubescens was evaluated in separate and mixed cultures, under different light intensities and qualities (green, red, and white), and at two different temperatures, chosen as representative of the natural conditions favoring the respective blooms of each species. In monocultures, the P. rubescens strain appeared to be particularly well adapted to low intensities of green light and displayed a strong photoinhibition under high irradiance levels. The P. agardhii strain appeared less specialized with regard to light quality and also less sensitive to photoinhibition at higher irradiances. In competition experiments, temperature (15°C vs. 25°C) was the most important parameter in determining relative fitness of the species and competitive success. At 15°C, P. rubescens appeared to be much more competitive than P. agardhii, while P. agardhii was more competitive at 25°C. Under low irradiance, however, the pigmentation of these strains was of primary importance in determining the outcomes of the competition experiments. On the basis of our experimental results and on field observations, we propose that the successful growth leading to the proliferation of these two differently pigmented strains may largely depend on the combined conditions of light and temperature. The two strains, being genetically close relatives, could therefore be considered as two ecotypes that are adapted to different light and temperature environments. Competition experiments showed that the combination of these parameters largely controls the success of one strain in comparison to the other.
TL;DR: Investigation of photoinhibition in Synechocystis sp.
Abstract: Recent investigations of photoinhibition have revealed that photodamage to photosystem II (PSII) involves two temporally separated steps: the first is the inactivation of the oxygen-evolving complex by light that has been absorbed by the manganese cluster and the second is the impairment of the photochemical reaction center by light that has been absorbed by chlorophyll. Our studies of photoinhibition in Synechocystis sp. PCC 6803 at various temperatures demonstrated that the first step in photodamage is not completed at low temperatures, such as 10°C. Further investigations suggested that an intermediate state, which is stabilized at low temperatures, might exist at the first stage of photodamage. The repair of PSII involves many steps, including degradation and removal of the D1 protein, synthesis de novo of the precursor to the D1 protein, assembly of the PSII complex, and processing of the precursor to the D1 protein. Detailed analysis of photodamage and repair at various temperatures has demonstrated that, among these steps, only the synthesis of the precursor to D1 appears to proceed at low temperatures. Investigations of photoinhibition at low temperatures have also indicated that prolonged exposure of cyanobacterial cells or plant leaves to strong light diminishes their ability to repair PSII. Such non-repairable photoinhibition is caused by inhibition of the processing of the precursor to the D1 protein after prolonged illumination with strong light at low temperatures.
TL;DR: The hypothesis that a decrease in the redox potential of QA causes an increase in singlet oxygen-mediated photoinhibition by favoring the back-reaction route that involves formation of the reaction center chlorophyll triplet is supported.
TL;DR: Growth of Arabidopsis in a UV-B-enhanced light regime increased tolerance to high light exposure and drought stress and higher tolerance to drought stress may be attributed to both increased proline content and decreased stomatal conductance.
Abstract: Arabidopsis thaliana grown in a light regime that included ultraviolet-B (UV-B) radiation (6 kJ m−2 d−1) had similar light-saturated photosynthetic rates but up to 50% lower stomatal conductance rates, as compared to plants grown without UV-B radiation. Growth responses of Arabidopsis to UV-B radiation included lower leaf area (25%) and biomass (10%) and higher UV-B absorbing compounds (30%) and chlorophyll content (52%). Lower stomatal conductance rates for plants grown with UV-B radiation were, in part, due to lower stomatal density on the adaxial surface. Plants grown with UV-B radiation had more capacity to down regulate photochemical efficiency of photosystem II (PSII) as shown by up to 25% lower φPSII and 30% higher non-photochemical quenching of chlorophyll fluorescence under saturating light. These contributed to a smaller reduction in the maximum photochemical efficiency of PSII (Fv/Fm), greater dark-recovery of Fv/Fm, and higher light-saturated carbon assimilation and stomatal conductance and transpiration rates after a four-hour high light treatment for plants grown with UV-B radiation. Plants grown with UV-B were more tolerant to a 12 day drought treatment than plants grown without UV-B as indicated by two times higher photosynthetic rates and 12% higher relative water content. UV-B-grown plants also had three times higher proline content. Higher tolerance to drought stress for Arabidopsis plants grown under UV-B radiation may be attributed to both increased proline content and decreased stomatal conductance. Growth of Arabidopsis in a UV-B-enhanced light regime increased tolerance to high light exposure and drought stress.