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Showing papers on "Photosynthesis published in 2005"


Journal ArticleDOI
TL;DR: In this article, it was shown that an increase in capacity of bean root cells to oxidize NADPH when exposed to K deficiency was up to 8-fold higher in plants with low K supply than in K-sufficient plants.
Abstract: Plants exposed to environmental stress factors, such as drought, chilling, high light intensity, heat, and nutrient limitations, suffer from oxidative damage catalyzed by reactive oxygen species (ROS), e.g., superoxide radical (O2 -), hydrogen peroxide (H2O2) and hydroxyl radical (OH ). Reactive O2 species are known to be primarily responsible for impairment of cellular function and growth depression under stress conditions. In plants, ROS are predominantly produced during the photosynthetic electron transport and activation of membrane-bound NAD(P)H oxidases. Increasing evidence suggests that improvement of potassium (K)-nutritional status of plants can greatly lower the ROS production by reducing activity of NAD(P)H oxidases and maintaining photosynthetic electron transport. Potassium deficiency causes severe reduction in photosynthetic CO2 fixation and impairment in partitioning and utilization of photosynthates. Such disturbances result in excess of photosynthetically produced electrons and thus stimulation of ROS production by intensified transfer of electrons to O2. Recently, it was shown that there is an impressive increase in capacity of bean root cells to oxidize NADPH when exposed to K deficiency. An increase in NADPH oxidation was up to 8-fold higher in plants with low K supply than in K-sufficient plants. Accordingly, K deficiency also caused an increase in NADPH-dependent O2 - generation in root cells. The results indicate that increases in ROS production during both photosynthetic electron transport and NADPH-oxidizing enzyme reactions may be involved in membrane damage and chlorophyll degradation in K-deficient plants. In good agreement with this suggestion, increases in severity of K deficiency were associated with enhanced activity of enzymes involved in detoxification of H2O2 (ascorbate peroxidase) and utilization of H2O2 in oxidative processes (guaiacol peroxidase). Moreover, K-deficient plants are highly light-sensitive and very rapidly become chlorotic and necrotic when exposed to high light intensity. In view of the fact that ROS production by photosynthetic electron transport and NADPH oxidases is especially high when plants are exposed to environmental stress conditions, it seems reasonable to suggest that the improvement of K-nutritional status of plants might be of great importance for the survival of crop plants under environmental stress conditions, such as drought, chilling, and high light intensity. Several examples are presented here emphasizing the roles of K in alleviating adverse effects of different abiotic stress factors on crop production.

1,059 citations


BookDOI
29 Mar 2005
TL;DR: The principles of Photosynthesis Mechanisms, Mechanisms of Photosynthetic Oxygen Evolution and the Fundamental Hypotheses of photosynthesis, and Recent Advances in Chloroplast Development in Higher Plants are explained.
Abstract: Preface Principles of Photosynthesis Mechanisms of Photosynthetic Oxygen Evolution and the Fundamental Hypotheses of Photosynthesis (Yuzeir Zeinalov) Thermoluminescence as a Tool in the study of Photosynthesis (Anil S. Bhagwat and Swapan K. Bhattachrjee) Biochemistry of Photosynthesis Chlorophyll Biosynthesis - A review (Benoit Schoefs and Martine Bertrand) Chloroplast Biogenesis 90, Probing the Relationship between Chlorophyll Biosynthetic Routes and the Topography of Chloroplast Biogenesis by Resonance Excitation Energy Transfer Determinations (Constantin A. Rebeiz, Karen J. Kopetz, and Vladimir L. Kolossov, USA) Protochlorophyllide Photoreduction - A review (Martine Bertrand and Benoit Schoefs) Formation and Demolition of Chloroplast during Leaf Ontogeny (Basanti Biswal) Role of Phosphorus in Photosynthetic Carbon Metabolism (Anna M. Rychter and I.M. Rao) Inhibition on Inactivation of Higher Plant Chloroplast Electron Transport (Rita Barr and Frederick L. Crane) Molecular Aspects of Photosynthesis: Photosystems, Photosynthetic Enzymes and Genes Photosystem I Structures and Functions (Teisuo Hiyama) Covalent Modification of Photosystem II Reaction-Center Polypeptides (Julian P. Whitelegge) Reactive Oxygen Species as Signaling Molecules Controlling Stress Adaptation in Plants (Tsanko Gechev, Ilya Gadjev, Stefan Dukiandjiev, and Ivan Minkov) Plastid Morphogenesis (Jan Hudak, Eliska Galova, and Lenka Zemanova) Plastid Proteases (Dennis E. Buetow) Supramolecular Organization of Water-Soluble Photosynthetic Enzymes Along the Thylakoid Membranes in Chloroplasts (Jayashree K. Sainis and Michael Melzer) Cytochrome C6 Genes in Cyanobacteria and Higher Plants (Kwok Ki Ho) Atmospheric and Environmental Factors Affecting Photosynthesis External and Internal Factors Responsible for Midday Depression of Photosynthesis (Da-Quan Xu and Yun-Kang Shen) Root Oxygen Depravation and the Reduction of Leaf Stomatal Aperture and Gas Exchange Effects on Photosynthesis (R.E. Sojka, H.D. Scott, and D.M. Oosterhuis) Rising Atmospheric CO2 and C4 Photosynthesis (Joseph C.V. Vu) Influence of High Light Intensity on Photosynthesis: Photoinhibition and Energy Dissipation (Robert Carpentier) Development of Functional Thylakoid Membranes: Regulation by Light and Hormones (Peter Nyitrai) Photosynthetic Pathways in Various Crop Plants Photosynthetic Carbon Assimilation of C3, C4 and CAM Pathways (Anil S. Bhagwat) Photosynthesis in Non-Typical C4 Species (Maria Valeria Lara and Carlos Santiago Andreo) Photosynthesis in Lower and Monocellular Plants Regulation of Phycobilisome Biosynthesis and Degradation in Cyanobacteria (Johannes Geiselmann, Jean Houmard, and Benoit Schoefs) Photosynthesis in Higher Plants Short-Term and Long-Term Regulation of Photosynthesis During Leaf Development (Dan Stessman, Martin Spalding, and Steven Rodermel) Recent Advances in Chloroplast Development in Higher Plants (Ilia D. Denev, Galina T. Yahubian, and Ivan N. Minkov) Photosynthesis in Different Plant Parts Photosynthesis in Leaf, Stem, Flower, and Fruit (Abdul Wahid, and Ejaz Rasul) Photosynthesis and Plant/Crop Productivity and Photosynthetic Products Photosynthetic Plant Productivity (Lubomir Natr and David W. Lawlor) Photosynthates Formation and Partitioning in Crop Plants (Alberto A. Iglesias and F.E. Podesta) Photosynthesis and Plant Genetics Crop Radiation Use Efficiency - Avenue for Genetic Improvement (G.V. Subbarao, O. Ito, and W.L. Berry) Physiological Perspectives on Improving Crop Adaptation to Drought - Justification for a Systemic Compnent-Based Approach (G.V. Subbarao, O. Ito, R. Serraj, J.H. Crouch, S. Tobita, K. Okada, C.T. Hash, R. Ortiz, and W.L. Berry) Photosynthetic Activity Measurements and Analysis of Photosynthetic Pigments Whole-Plant CO2 Exchange as a Non-Invasive Tool for Measuring Growth (Evangelos D. Leonardos, and Bernard Grodzinski) Approaches to Measuring Plant Photosynthetic Activity (Elena Masarovicova and Katarina Kralova) Analysis of Photosynthetic Pigments: An Update (Martine Bertrand, Jose L. Garrido, and Benoit Schoefs) Photosynthesis and Its Relationship with other Plant Physiological Processes Photosynthesis, Respiration, and the Limits to Growth (Bruce N. Smith, Heidi A. Summers, Emily A. Keller, and Tonya Thygerson) Nitrogen Assimilation and Carbon Metabolism (Alberto A. Iglesias, Maria J. Estrella, and Fernando Pieckenstain) Leaf Senescence (Agnieszka Mostowska) Photosynthesis Under Environmental Stress Conditions Photosynthesis in Plants under Stressful Conditions (Rama Shanker Dubey) Photosynthetic Response of Green Plants to Environmental Stress: Inhibition of Photosynthesis and Adaptational Mechanisms (Basanti Biswal) Salt and Drought Stress Effects on Photosynthesis, Enzyme Cohesion and High Turn Over Metabolite Shuttling, Essential for Functioning of Pathways, Is Impaired by Changes in Cytosolic Water Potential (B, Huchzermeyer and H.W. Koyro) Photosynthetic Carbon Metabolism of Crops under Salt Stress (Bruria Heuer) Photosynthesis under Drought Stress (Habib-ur-Rahman Athar and Muhammad Ashraf) Role of Plant Growth Regulators in Stomatal Limitation to Photosynthesis During Water Stress (Jana Pospisilova and Ian C. Dodd) Adverse Effects of UV-B Light on the Structure and Function of the Photosynthetic Apparatus (Imre Vass, Andras Szilard, and Cosmin Sicora) Heavy Metal Toxicity Induced Alterations in Photosynthetic Metabolism in Plants (Shruti Mishra and R.S, Dubey) Effects of Heavy Metals on Chlorophyll-Protein Complexes in Higher Plants: Causes and Consequences (Eva Sarvari) Photosynthesis in the Past, Present, and Future The Origin and Evolution of C4 Photosynthesis (Bruce N. Smith)

569 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that moderate heat stress can stimulate dark reduction of plastoquinone and cyclic electron flow in the light and increase thylakoid leakiness.
Abstract: Photosynthesis is particularly sensitive to heat stress and recent results provide important new insights into the mechanisms by which moderate heat stress reduces photosynthetic capacity. Perhaps most surprising is that there is little or no damage to photosystem II as a result of moderate heat stress even though moderate heat stress can reduce the photosynthetic rate to near zero. Moderate heat stress can stimulate dark reduction of plastoquinone and cyclic electron flow in the light. In addition, moderate heat stress may increase thylakoid leakiness. At the same time, rubisco deactivates at moderately high temperature. Relationships between effects of moderate heat on rubisco activation and thylakoid reactions are not yet clear. Reactive oxygen species such as H 2 O 2 may also be important during moderate heat stress. Rubisco can make hydrogen peroxide as a result of oxygenase side reactions and H 2 O 2 production by rubisco was recently shown to increase substantially with temperature. The ability to withstand moderately high temperature can be improved by altering thylakoid lipid composition or by supplying isoprene. In my opinion this indicates that thylakoid reactions are important during moderate heat stress. The deactivation of rubisco at moderately high temperature could be a parallel deleterious effect or a regulatory response to limit damage to thylakoid reactions.

539 citations


Journal ArticleDOI
TL;DR: Heat led to a sun-type adaptation response of the photosynthesis pigment apparatus for the Nagcarlang genotype, but not for Campbell-28, and thus an increase in chlorophyll a/b ratio and a decrease inchlorophyll/carotenoid ratio were shown in Nag carlang stressed plants.

522 citations


Journal ArticleDOI
TL;DR: The SPAD-502 has been shown to be a good tool to diagnose the integrity of the photosynthetic system in coffee leaves, and can thus help in the advanced interpretations of the photochemical process of these plants.

498 citations


Journal ArticleDOI
TL;DR: The model provides a synthetic, mechanistic framework for linking global biogeochemical cycles to cellular-, individual- and community-level processes and supports the hypothesis that the combined effects of body size and temperature on individual metabolic rate impose important constraints on the global C cycle.
Abstract: Summary 1. We present a model that yields ecosystem-level predictions of the flux, storage and turnover of carbon in three important pools (autotrophs, decomposers, labile soil C) based on the constraints of body size and temperature on individual metabolic rate. 2. The model predicts a 10 000-fold increase in C turnover rates moving from tree- to phytoplankton-dominated ecosystems due to the size dependence of photosynthetic rates. 3. The model predicts a 16-fold increase in rates controlled by respiration (e.g. decomposition, turnover of labile soil C and microbial biomass) over the temperature range 0‐30 °C due to the temperature dependence of ATP synthesis in respiratory complexes. 4. The model predicts only a fourfold increase in rates controlled by photosynthesis (e.g. net primary production, litter fall, fine root turnover) over the temperature range 0‐30 °C due to the temperature dependence of Rubisco carboxylation in chloroplasts. 5. The difference between the temperature dependence of respiration and photosynthesis yields quantitative predictions for distinct phenomena that include acclimation of plant respiration, geographic gradients in labile C storage, and differences between the short- and long-term temperature dependence of whole-ecosystem CO2 flux. 6. These four sets of model predictions were tested using global compilations of data on C flux, storage and turnover in ecosystems. 7. Results support the hypothesis that the combined effects of body size and temperature on individual metabolic rate impose important constraints on the global C cycle. The model thus provides a synthetic, mechanistic framework for linking global biogeochemical cycles to cellular-, individual- and community-level processes.

469 citations


Journal ArticleDOI
Fashui Hong1, Juan Zhou1, Chao Liu1, Fan Yang1, Cheng Wu1, Lei Zheng1, Ping Yang1 
TL;DR: It is suggested that photosynthesis promoted by nano-TiO2 might be related to activation of photochemical reaction of chloroplasts of spinach.
Abstract: The effects of nano-TiO2 (rutile) on the photochemical reaction of chloroplasts of spinach were studied. The results showed that when spinach was treated with 0.25% nano-TiO2, the Hill reaction, such as the reduction rate of FeCy, and the rate of evolution oxygen of chloroplasts was accelerated and noncyclic photophosphorylation (nc-PSP) activity of chloroplasts was higher than cyclic photophosphorylation (c-PSP) activity, the chloroplast coupling was improved and activities of Mg2+-ATPase and chloroplast coupling factor I (CF1)-ATPase on the thylakoid membranes were obviously activated. It suggested that photosynthesis promoted by nano-TiO2 might be related to activation of photochemical reaction of chloroplasts of spinach.

387 citations


Journal ArticleDOI
TL;DR: It is shown that photosynthetic capacity per unit area and plant yield can be increased by overexpressing a single native plant enzyme, SBPase, and that this gives an advantage to the growth of these plants from an early phase of vegetative growth.
Abstract: Activity of the Calvin cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase) was increased by overexpression of an Arabidopsis (Arabidopsis thaliana) cDNA in tobacco (Nicotiana tabacum) plants. In plants with increased SBPase activity, photosynthetic rates were increased, higher levels of Suc and starch accumulated during the photoperiod, and an increase in leaf area and biomass of up to 30% was also evident. Light saturated photosynthesis increased with increasing SBPase activity and analysis of CO2 response curves revealed that this increase in photosynthesis could be attributed to an increase in ribulose 1,5-bisphosphate regenerative capacity. Seedlings with increased SBPase activity had an increased leaf area at the 4 to 5 leaf stage when compared to wild-type plants, and chlorophyll fluorescence imaging of these young plants revealed a higher photosynthetic capacity at the whole plant level. Measurements of photosynthesis, made under growth conditions integrated over the day, showed that mature plants with increased SBPase activity fixed 6% to 12% more carbon than equivalent wild-type leaves, with the young leaves having the highest rates. In this paper, we have shown that photosynthetic capacity per unit area and plant yield can be increased by overexpressing a single native plant enzyme, SBPase, and that this gives an advantage to the growth of these plants from an early phase of vegetative growth. This work has also shown that it is not necessary to bypass the normal regulatory control of SBPase, exerted by conditions in the stroma, to achieve improvements in carbon fixation.

366 citations


Journal ArticleDOI
TL;DR: It is shown that the repression of this mitochondrially localized enzyme improves both carbon assimilation and aerial growth in a crop species.
Abstract: Transgenic tomato (Solanum lycopersicum) plants expressing a fragment of the mitochondrial malate dehydrogenase gene in the antisense orientation and exhibiting reduced activity of this isoform of malate dehydrogenase show enhanced photosynthetic activity and aerial growth under atmospheric conditions (360 ppm CO2). In comparison to wild-type plants, carbon dioxide assimilation rates and total plant dry matter were up to 11% and 19% enhanced in the transgenics, when assessed on a whole-plant basis. Accumulation of carbohydrates and redox-related compounds such as ascorbate was also markedly elevated in the transgenics. Also increased in the transgenic plants was the capacity to use l-galactono-lactone, the terminal precursor of ascorbate biosynthesis, as a respiratory substrate. Experiments in which ascorbate was fed to isolated leaf discs also resulted in increased rates of photosynthesis providing strong indication for an ascorbate-mediated link between the energy-generating processes of respiration and photosynthesis. This report thus shows that the repression of this mitochondrially localized enzyme improves both carbon assimilation and aerial growth in a crop species.

335 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined kidney bean plants, with developing gradually water stress for several days after watering and then permitted to recover by re-watering, showing that the critical time for the recovery of photosynthesis was recognized.

324 citations


Journal ArticleDOI
TL;DR: This work describes the isolation and cultivation of a previously unknown green sulfur bacterial species from a deep-sea hydrothermal vent, where the only source of light is geothermal radiation that includes wavelengths absorbed by photosynthetic pigments of this organism.
Abstract: The abundance of life on Earth is almost entirely due to biological photosynthesis, which depends on light energy. The source of light in natural habitats has heretofore been thought to be the sun, thus restricting photosynthesis to solar photic environments on the surface of the Earth. If photosynthesis could take place in geothermally illuminated environments, it would increase the diversity of photosynthetic habitats both on Earth and on other worlds that have been proposed to possibly harbor life. Green sulfur bacteria are anaerobes that require light for growth by the oxidation of sulfur compounds to reduce CO 2 to organic carbon, and are capable of photosynthetic growth at extremely low light intensities. We describe the isolation and cultivation of a previously unknown green sulfur bacterial species from a deep-sea hydrothermal vent, where the only source of light is geothermal radiation that includes wavelengths absorbed by photosynthetic pigments of this organism.

Journal ArticleDOI
TL;DR: A review of recent findings regarding the nature of singlet-oxygen responses in the chloroplast will discuss some intriguing new findings in that area, focusing on recent findings about responses to singlet oxygen.
Abstract: Photosynthetic organisms constantly face the threat of photo-oxidative stress from fluctuating light conditions and environmental stress. Plants and algae have developed an array of defences to protect the chloroplast from reactive oxygen species. Genetic and physiological studies have shown that antioxidant responses are important to high-light acclimation, both by directly scavenging or quenching reactive oxygen intermediates and by contributing reducing power for alternative electron transport pathways and excess energy dissipation. At present, the signalling events leading to up-regulation of antioxidant defences in high light remain a mystery. Recent advances toward understanding acclimation to oxidative stress in both photosynthetic and non-photosynthetic model organisms may illuminate how plants and algae respond to high-light stress. Although the role of hydrogen peroxide in high-light acclimation has been investigated, less is known about responses to singlet oxygen, a form of reactive oxygen that poses a significant threat specifically to photosynthetic organisms. This review will discuss some intriguing new findings in that area, focusing on recent findings regarding the nature of singlet-oxygen responses in the chloroplast.

Journal ArticleDOI
TL;DR: Investigation of mature non-senescent leaves of Laurus nobilis, Olea europea and Quercus ilex demonstrates that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations.
Abstract: Leaf age-dependent changes in structure, nitrogen content, internal mesophyll diffusion conductance ( g m ), the capacity for photosynthetic electron transport ( J max ) and the maximum carboxylase activity of Rubisco ( V cmax ) were investigated in mature non-senescent leaves of Laurus nobilis L., Olea europea L. and Quercus ilex L. to test the hypothesis that the relative significance of biochemical and diffusion limitations of photosynthesis changes with leaf age. The leaf life-span was up to 3 years in L. nobilis and O. europea and 6 years in Q. ilex . Increases in leaf age resulted in enhanced leaf dry mass per unit area ( M A ), larger leaf dry to fresh mass ratio, and lower nitrogen contents per dry mass ( N M ) in all species, and lower nitrogen contents per area ( N A ) in L. nobilis and Q. ilex . Older leaves had lower g m , J max and V cmax . Due to the age-dependent increase in M A , mass-based g m , J max and V cmax declined more strongly (7- to 10-fold) with age than area-based (5- to 7-fold) characteristics. Diffusion conductance was positively associated with foliage photosynthetic potentials. However, this correlation was curvilinear, leading to lower ratio of chloroplastic to internal CO 2 concentration ( C c / C i ) and larger drawdown of CO 2 from leaf internal air space to chloroplasts ( D C ) in older leaves with lower g m . Overall the agedependent decreases in photosynthetic potentials were associated with decreases in N M and in the fraction of N in photosynthetic proteins, whereas decreases in g m were associated with increases in M A and the fraction of cell walls. These age-dependent modifications altered the functional scaling of foliage photosynthetic potentials with M A , N M , and N A . The species primarily differed in the rate of agedependent modifications in foliage structural and functional characteristics, but also in the degree of agedependent changes in various variables. Stomatal openness was weakly associated with leaf age, but due to species differences in stomatal openness, the distribution of total diffusion limitation between stomata and mesophyll varied among species. These data collectively demonstrate that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations. Age-dependent changes in g m and photosynthetic capacities do not occur in a co-ordinated manner in these species such that mesophyll diffusion constraints curb photosynthesis more in older than in younger leaves.

Journal ArticleDOI
TL;DR: Light increases the survival of terrestrial plants under water, indicating that photosynthesis commonly occurs under these submerged conditions, and thereby alleviates the adverse effects of flooding.

Journal ArticleDOI
TL;DR: In vivo probes of the proton circuit in wild-type and a mutant strain of Arabidopsis thaliana show that regulation of light capture is modulated primarily by altering the resistance of proton efflux from the thylakoid lumen, whereas modulation of propton influx through cyclic electron flow around photosystem I is suggested to play a role in regulating the ATP/NADPH output ratio of the light reactions.
Abstract: In higher plant chloroplasts, transthylakoid proton motive force serves both to drive the synthesis of ATP and to regulate light capture by the photosynthetic antenna to prevent photodamage. In vivo probes of the proton circuit in wild-type and a mutant strain of Arabidopsis thaliana show that regulation of light capture is modulated primarily by altering the resistance of proton efflux from the thylakoid lumen, whereas modulation of proton influx through cyclic electron flow around photosystem I is suggested to play a role in regulating the ATP/NADPH output ratio of the light reactions.

Journal ArticleDOI
TL;DR: Cd2+ in the low-microM range inhibited photoactivation in Chlamydomonas reinhardtii and in isolated Photosystem II, suggesting that this event is also involved in the Cd2-induced inhibition of photosynthesis in vivo.

Journal ArticleDOI
TL;DR: The stable population of green sulfur bacteria in the Black Sea chemocline represents the most extremely low-light-adapted and slowest-growing type of phototroph known to date.
Abstract: The biomass, phylogenetic composition, and photoautotrophic metabolism of green sulfur bacteria in the Black Sea was assessed in situ and in laboratory enrichments. In the center of the western basin, bacteriochlorophyll e (BChl e) was detected between depths of 90 and 120 m and reached maxima of 54 and 68 ng liter−1. High-pressure liquid chromatography analysis revealed a dominance of farnesyl esters and the presence of four unusual geranyl ester homologs of BChl e. Only traces of BChl e (8 ng liter−1) were found at the northwestern slope of the Black Sea basin, where the chemocline was positioned at a significantly greater depth of 140 m. Stable carbon isotope fractionation values of farnesol indicated an autotrophic growth mode of the green sulfur bacteria. For the first time, light intensities in the Black Sea chemocline were determined employing an integrating quantum meter, which yielded maximum values between 0.0022 and 0.00075 μmol quanta m−2 s−1 at the top of the green sulfur bacterial layer around solar noon in December. These values represent by far the lowest values reported for any habitat of photosynthetic organisms. Only one 16S rRNA gene sequence type was detected in the chemocline using PCR primers specific for green sulfur bacteria. This previously unknown phylotype groups with the marine cluster of the Chlorobiaceae and was successfully enriched in a mineral medium containing sulfide, dithionite, and freshly prepared yeast extract. Under precisely controlled laboratory conditions, the enriched green sulfur bacterium proved to be capable of exploiting light intensities as low as 0.015 μmol quanta m−2 s−1 for photosynthetic 14CO2 fixation. Calculated in situ doubling times of the green sulfur bacterium range between 3.1 and 26 years depending on the season, and anoxygenic photosynthesis contributes only 0.002 to 0.01% to total sulfide oxidation in the chemocline. The stable population of green sulfur bacteria in the Black Sea chemocline thus represents the most extremely low-light-adapted and slowest-growing type of phototroph known to date.

Journal ArticleDOI
TL;DR: Results show that up-regulation of the respiratory AOX pathway protects the photosynthetic electron transport chain from the harmful effects of excess light.
Abstract: The aim of this study was to explore the role of the mitochondrial alternative oxidase (AOX) in the protection of photosynthesis during drought in wheat leaves. The relative water contents of water-replete and drought-exposed wheat plants were 97.2+/-0.3 and 75+/-2, respectively. Drought increased the amount of leaf AOX protein and also enhanced the rate of AOX-dependent O(2) uptake by the respiratory electron transport chain. The amount of the reduced, active form of the AOX protein was specifically increased by drought. The AOX inhibitor salicylhydroxamic acid (1 mM; SHAM) inhibited 70% of AOX activity in vivo in both water-replete and drought-exposed plants. Plants treated with SHAM were then exposed to low (100), high (350), or excess light (800 mumol photons m(-2) s(-1)) for 90 min. SHAM did not modify chlorophyll a fluorescence quenching parameters in water-replete controls after any of these treatments. However, while the maximal quantum yield of photosystem II (PSII) electron transport (F(v)/F(m)) was not affected by SHAM, the immediate quantum yield of PSII electron transport (Phi(PSII)) and photochemical quenching (qP) were gradually reduced by increasing irradiance in SHAM-treated drought-exposed plants, the decrease being most pronounced at the highest irradiance. Non-photochemical quenching (NPQ) reached near maximum levels in plants subjected to drought at high irradiance. However, a combination of drought and low light caused an intermediate increase in NPQ, which attained higher values when AOX was inhibited. Taken together, these results show that up-regulation of the respiratory AOX pathway protects the photosynthetic electron transport chain from the harmful effects of excess light.

Journal ArticleDOI
TL;DR: It is proposed that in photoautotrophic leaves, photosynthesis and assimilatory metabolism must be switched off to initiate respiration and other processes required for defence.
Abstract: The metabolic and cellular changes in source leaves of Nicotiana tabacum L. cv SNN during an incompatible interaction with Phytophthora nicotianae van Breda de Haan were investigated and compared with defence reactions. Hypersensitive cell death was preceded by a rapid and highly localized shift to non-assimilatoric metabolism. During the first 6 h post infection (hpi), reactive oxygen species (ROS) accumulated. Callose was deposited at the interface of adjacent mesophyll cells (≥1 hpi), the export of sucrose collapsed and its content in the apoplast increased. Stomata closed and photosynthetic flux was reallocated from CO 2 assimilation in favour of photorespiration. This was accompanied by an increase in respiration, glucose-6-phosphate dehydrogenase (G6PDH) activity, apoplastic invertase and hexose content. Later (>6 hpi) the photosynthetic electron transport chain was interrupted and photosynthesis completely collapsed. This was accompanied by a further increase in apoplastic invertase and carbohydrates, respiration and oxidative pentose phosphate pathway (OPPP) and followed by further burst in ROS release. Hypersensitive cell death did not appear until photosynthesis completely declined. Photosynthesis was visualized by chlorophyll-a fluorescence imaging on a macro- and microscopic scale. Decline in photosynthesis and defence reactions were highly localized processes, which occur in single mesophyll cells. We propose that in photoautotrophic leaves, photosynthesis and assimilatory metabolism must be switched off to initiate respiration and other processes required for defence. An early blockage of intercellular sugar transportation, due to callose deposition, in conjunction with enhanced apoplastic invertase activity could facilitate this metabolic shift.

Journal ArticleDOI
TL;DR: Photosynthetic acclimation to low temperature in spinach leaves was due not only to the change in the balance of the absolute rates of RuBP regeneration and carboxylation but also to the largechange in the optimum temperature of Ru BP carboxesylation.
Abstract: Spinach (Spinacia oleracea) plants were grown under the day/night temperature regime of 15/10 °C (LT) or 30/25 °C (HT). The plants were also transferred from HT to LT when the sample leaves were at particular developmental stages (HL-transfer). With fully mature leaves, the light-saturated photosynthetic rate (A) at the ambient CO2 concentration (Ca) of 1500 µL L−1 (A1500) and the initial slope of A versus intercellular CO2 concentration (Ci) at low Ci region (IS) were obtained to assess capacities of RuBP regeneration and carboxylation. Photosynthetic components including Rubisco and cytochrome f (Cyt f) were also determined. The optimum temperatures for A at Ca of 360 µL L−1 (A360), A1500 and IS in HT leaves were 27, 36 and 24 °C, whereas those in LT leaves were 18, 30 and 18 °C. The optimum temperatures in HL-transfer leaves approached those of LT leaves with the increase in the duration at LT. The shift in the optimum temperature was greater and quicker for IS than A1500. By the HL-transfer, the maximum values of A1500 and IS also increased. The maximum A1500 and Cyt f content increased more promptly than IS and Rubisco content. Changes in the Cyt f/Rubisco ratio were reflected to those in the A1500/IS ratio. Taken together, photosynthetic acclimation to low temperature in spinach leaves was due not only to the change in the balance of the absolute rates of RuBP regeneration and carboxylation but also to the large change in the optimum temperature of RuBP carboxylation.

Journal ArticleDOI
TL;DR: Experimental data will be provided showing that the isozyme from pea leaf chloroplasts is activated by reduced thioredoxin f or m in a similar way, and recent evidence will be discussed showing that key enzymes of de novo fatty acid synthesis and ammonium assimilation are regulated by reversible disulphide-bond formation similar to AGPase.
Abstract: Redox signals generated by the photosynthetic electron transport chain are known to be involved in regulating the Calvin cycle, ATP synthesis, and NADPH export from chloroplasts in response to light. The signal cascade involves transfer of electrons from photosystem I via the ferredoxin-thioredoxin system to target enzymes that are activated by reduction of regulatory disulphide bonds. The purpose of this review is to discuss recent findings showing that this concept can be extended to the regulation of carbon storage and partitioning in plants. Starch is the major carbon store in plants, and ADP-glucose pyrophosphorylase (AGPase) is the key regulatory enzyme of starch synthesis in the plastid. It has been shown that AGPase from potato tubers is subject to post-translational redox modification, and here experimental data will be provided showing that the isozyme from pea leaf chloroplasts is activated by reduced thioredoxin f or m in a similar way. Recent reports will be summarized providing in planta evidence that this mechanism regulates storage starch synthesis in response to light and sugars. Post-translational redox activation of AGPase in response to sugars is part of a signalling mechanism linking the rate of starch synthesis to the availability of carbon in diverse plant tissues. Some of the components of the signalling pathway reporting changes in the cytosolic sugar status to the plastid have been postulated, but detailed work is in progress to confirm the exact mode of action. Recent evidence will be discussed showing that key enzymes of de novo fatty acid synthesis (acetyl-CoA carboxylase) and ammonium assimilation (glutamine synthetase and glutamine:oxoglutarate amino transferase) are regulated by reversible disulphide-bond formation similar to AGPase. Redox regulation is proposed to be the preferred strategy of plastidial enzymes to regulate various metabolic processes such as carbon fixation, starch metabolism, lipid synthesis, and amino acid synthesis in response to physiological and environmental inputs.

Journal ArticleDOI
TL;DR: In conclusion, superior N-use efficiency of NADP-ME relative to NAD-ME grasses was achieved with less leaf N, soluble protein, and Rubisco having a faster kcat.
Abstract: In 27 C4 grasses grown under adequate or deficient nitrogen (N) supplies, N-use efficiency at the photosynthetic (assimilation rate per unit leaf N) and whole-plant (dry mass per total leaf N) level was greater in NADP-malic enzyme (ME) than NAD-ME species. This was due to lower N content in NADP-ME than NAD-ME leaves because neither assimilation rates nor plant dry mass differed significantly between the two C4 subtypes. Relative to NAD-ME, NADP-ME leaves had greater in vivo (assimilation rate per Rubisco catalytic sites) and in vitro Rubisco turnover rates (kcat; 3.8 versus 5.7 s−1 at 25°C). The two parameters were linearly related. In 2 NAD-ME (Panicum miliaceum and Panicum coloratum) and 2 NADP-ME (Sorghum bicolor and Cenchrus ciliaris) grasses, 30% of leaf N was allocated to thylakoids and 5% to 9% to amino acids and nitrate. Soluble protein represented a smaller fraction of leaf N in NADP-ME (41%) than in NAD-ME (53%) leaves, of which Rubisco accounted for one-seventh. Soluble protein averaged 7 and 10 g (mmol chlorophyll)−1 in NADP-ME and NAD-ME leaves, respectively. The majority (65%) of leaf N and chlorophyll was found in the mesophyll of NADP-ME and bundle sheath of NAD-ME leaves. The mesophyll-bundle sheath distribution of functional thylakoid complexes (photosystems I and II and cytochrome f) varied among species, with a tendency to be mostly located in the mesophyll. In conclusion, superior N-use efficiency of NADP-ME relative to NAD-ME grasses was achieved with less leaf N, soluble protein, and Rubisco having a faster kcat.

Journal ArticleDOI
TL;DR: Data indicate that several metabolic down-regulations (glycolysis, Krebs cycle) accompany the light/dark transition and emphasize the decrease of the Krebs Cycle decarboxylations as a metabolic basis of the light-dependent inhibition of mitochondrial respiration.
Abstract: 13 C-enriched compounds. Using different positional 13 C-enrichments, it is shown that the Krebs cycle is reduced by 95% in the light and that the pyruvate dehydrogenase reaction is much less reduced, by 27% or less. Glucose molecules are scarcely metabolized to liberate CO 2 in the light, simply suggesting that they can rarely enter glycolysis. Nuclear magnetic resonance analysis confirmed this view; when leaves are fed with 13 C-glucose, leaf sucrose and glucose represent nearly 90% of the leaf 13 C content, demonstrating that glucose is mainly directed to sucrose synthesis. Taken together, these data indicate that several metabolic down-regulations (glycolysis, Krebs cycle) accompany the light/dark transition and emphasize the decrease of the Krebs cycle decarboxylations as a metabolic basis of the light-dependent inhibition of mitochondrial respiration. Illuminated leaves simultaneously assimilate CO 2 through the photosynthetic carbon reduction cycle and lose CO 2 through photorespiration and day respiration. In darkness, leaves no longer assimilate CO 2 via the photosynthetic carbon reduction cycle but produce CO 2 through dark respiration. Although dark respiration is known to involve glycolysis and CO 2 production through pyruvate dehydrogenation and the degradative Krebs cycle (Trethewey and ap Rees, 1994; Plaxton, 1996), the carbon metabolism that is responsible for the CO 2 respiratory release in the light is almost unknown. This is so because the day respiratory CO 2 flux is very low and masked by the photosynthetic carbon fixation and the photorespiratory CO2 production in the light, and is thus difficult to study. Nevertheless, it has been repeatedly shown, using either the Laisk’s (Laisk, 1977) or Kok’s method (Kok, 1948), that the rate of day respiration (Rd) is less than that of dark respiration (Rn; for review, see Atkin et al., 2000) so that light is known to inhibit respiration, with a R d /R n value (usually denoted as m) ranging from 30% to 100% (for a recent study, see Peisker and Apel, 2001). Pioneering gas exchange measurements on mustard suggested that some enzymatic activities are inhibited in the light so that substrates accumulate (Cornic, 1973), explaining the respiratory burst when leaves are darkened: the light enhanced dark respiration. More recently, it has been shown in the unicellular alga Selenastrum minutum that pyruvate kinase (Lin et al., 1989) is inhibited by light. It is also the case of the pyruvate dehydrogenase complex that is partly inactivated by (reversible) phosphorylation in extracts from illuminated leaves (Budde and Randall, 1990;

Journal ArticleDOI
TL;DR: Rapidly inducible non‐photochemical quenching (NPQ) is a short‐term response by which plants and eukaryotic algae dissipate excitation energy as heat.
Abstract: Efficient photosynthesis is of fundamental importance for plant survival and fitness. However, in oxygenic photosynthesis, the complex apparatus responsible for the conversion of light into chemical energy is susceptible to photodamage. Oxygenic photosynthetic organisms have therefore evolved several protective mechanisms to deal with light energy. Rapidly inducible non-photochemical quenching (NPQ) is a short-term response by which plants and eukaryotic algae dissipate excitation energy as heat. This review focuses on recent advances in the elucidation of the molecular mechanisms underlying this protective quenching pathway in higher plants.

Journal ArticleDOI
TL;DR: In this paper, the effects of exogenous application of glycinebetaine (GB) (10 mM) on growth, leaf water content, water use efficiency, photosynthetic gas exchange, and photosystem II photochemistry were investigated in maize plants subjected to salt stress (50 and 100 mM NaCI).
Abstract: The effects of exogenous application of glycinebetaine (GB) (10 mM) on growth, leaf water content, water use efficiency, photosynthetic gas exchange, and photosystem II photochemistry were investigated in maize plants subjected to salt stress (50 and 100 mM NaCI) Salt stress resulted in the decrease in growth and leaf relative water content as well as net photosynthesis and the apparent quantum yield of photosynthesis Stomatal conductance, evaporation rate, and water use efficiency were decreased in salt-stressed plants Salt stress also caused a decrease in the actual efficiency of PSII (Φ PSII ), the efficiency of excitation energy capture by open PSII reaction centers (F v '/F m '), and the coefficients of photochemical quenching (qp) but caused an increase in non-photochemical quenching (NPQ) Salt stress showed no effects on the maximal efficiency of PSII photochemistry (F v /F m ) On the other hand, in salt-stressed plants, GB application improved growth, leaf water content, net photosynthesis, and the apparent quantum yield of photosynthesis GB application also increased stomatal conductance, leaf evaporation rate, and water use efficiency In addition, GB application increased Φ PSII , F v '/F m ', and qp but decreased NPQ However, GB application showed no effects on F v /F m These results suggest that photosynthesis was improved by GB application in salt-stressed plants and such an improvement was associated with an improvement in stomatal conductance and the actual PSII efficiency

Journal ArticleDOI
TL;DR: Temperature and light-dependence of photosynthesis, and plastid and extraplastid red pigment composition of red snow algae (Chlamydomonas nivalis) from snow patches in the high Alps of Austria are studied to support the cryophilic adaptation of snow algal cells.
Abstract: Snow algae inhabit most of the cold regions worldwide, where long-lasting snow fields are common. The ecophysiology of snow algae has been studied intensively in North America and occasionally in polar regions. In the European Alps, the systematics of snow algae have been studied mainly by light microscopy. We studied temperature and light-dependence of photosynthesis, and plastid and extraplastid red pigment composition of red snow algae (Chlamydomonas nivalis) from snow patches in the high Alps of Austria. Both photosynthetic and respiratory data support the cryophilic adaptation of snow algal cells, but C. nivalis produced oxygen without any inhibition at temperatures up to 20°C and maintained this for 1 h, at irradiances up to 1800 µmol m−2s−1. Chlorophyll and primary carotenoid pigment composition was similar to that found in most other Chlorophyta. Additionally, large amounts of free and esterified astaxanthin were located in cytoplasmic lipid globules. Light and electron microscopy showed that the ...

Journal ArticleDOI
12 Jan 2005-Planta
TL;DR: It is demonstrated that the better performance of the ear under water stress (compared to the flag leaf) is not related to C4 or CAM photosynthesis, and drought tolerance of theEar is explained by its higher RWC in drought, and osmotic adjustment and xeromorphic traits of ear parts may be responsible.
Abstract: The photosynthetic characteristics of the ear and flag leaf of well-watered (WW) and water-stressed (WS) durum wheat (Triticum turgidum L. var. durum) were studied in plants grown under greenhouse and Mediterranean field conditions. Gas exchange measurements simultaneously with modulated chlorophyll fluorescence were used to study the response of the ear and flag leaf to CO2 and O2 during photosynthesis. C4 metabolism was identified by assessing the sensitivity of photosynthetic rate and electron transport to oxygen. The presence of CAM metabolism was assessed by measuring daily patterns of stomatal conductance and net CO2 assimilation. In addition, the histological distribution of Rubisco protein in the ear parts was studied by immunocytochemical localisation. Relative water content (RWC) and osmotic adjustment (osmotic potential at full turgor) were also measured in these organs. Oxygen sensitivity of the assimilation rate and electron transport, the lack of Rubisco compartmentalisation in the mesophyll tissues and the gas-exchange pattern at night indicated that neither C4 nor CAM metabolism occurs in the ear of WW or WS plants. Nevertheless, photosynthetic activity of the flag leaf was more affected by WS conditions than that of the ear, under both growing conditions. The lower sensitivity under water stress of the ear than of the flag leaf was linked to higher RWC and osmotic adjustment in the ear bracts and awns. We demonstrate that the better performance of the ear under water stress (compared to the flag leaf) is not related to C4 or CAM photosynthesis. Rather, drought tolerance of the ear is explained by its higher RWC in drought. Osmotic adjustment and xeromorphic traits of ear parts may be responsible.

Journal ArticleDOI
24 Feb 2005-Nature
TL;DR: This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat by demonstrating photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates in a shaded niche enriched in near-infrared light.
Abstract: The cyanobacterium known as Acaryochloris marina is a unique phototroph that uses chlorophyll d as its principal light-harvesting pigment instead of chlorophyll a, the form commonly found in plants, algae and other cyanobacteria; this means that it depends on far-red light for photosynthesis Here we demonstrate photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates (didemnid ascidians) in a shaded niche enriched in near-infrared light This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat

Journal ArticleDOI
01 Jan 2005-Planta
TL;DR: This first analysis of limitations to soybean photosynthesis under fully open-air conditions reveals important differences to prior studies that have used enclosures to elevate [CO2], most significantly a smaller response of Asat and an apparent shift in resources away from Rubisco relative to capacity for electron transport.
Abstract: Down-regulation of light-saturated photosyn- thesis (Asat) at elevated atmospheric CO2 concentration, (CO2), has been demonstrated for many C3 species and is often associated with inability to utilize additional photosynthate and/or nitrogen limitation. In soybean, a nitrogen-fixing species, both limitations are less likely than in crops lacking an N-fixing symbiont. Prior studies have used controlled environment or field enclosures where the artificial environment can modify responses to (CO2). A soybean free air (CO2) enrichment (FACE) facility has provided the first opportunity to analyze the effects of elevated (CO2) on photosynthesis under fully open-air conditions. Potential ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (Vc,max) and electron transport through photosystem II (Jmax) were determined from the responses of Asat to intercel- lular (CO2 )( Ci) throughout two growing seasons. Mesophyll conductance to CO2 (gm) was determined from the responses of Asat and whole chain electron transport (J) to light. Elevated (CO2) increased Asat by 15-20% even though there was a small, statistically significant, decrease in Vc,max. This differs from previous studies in that Vc,max/Jmax decreased, inferring a shift in resource investment away from Rubisco. This raised the Ci at which the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred. The decrease in Vc,max was not the result of a change in gm, which was unchanged by elevated (CO2). This first analysis of limitations to soy- bean photosynthesis under fully open-air conditions re- veals important differences to prior studies that have used enclosures to elevate (CO2), most significantly a smaller response of Asat and an apparent shift in re- sources away from Rubisco relative to capacity for electron transport.

Journal ArticleDOI
TL;DR: Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments more effectively than gas exchange measurements alone, and physiological restrictions to photosynthesis in leaves of water stressed cotton plants in a series of greenhouse experiments were investigated.
Abstract: Water stress may reduce leaf net photosynthetic carbon assimilation (AN) through both stomatal effects, which reduce the leaf internal CO 2 concentration (C 1 ), and nonstomatal effects, which result in reduced AN at a given level of C 1 . However, the leaf gas exchange techniques used to calculate C 1 are susceptible to important artifacts when applied to water-stressed leaves, making such C 1 estimates unreliable. As an alternative to C 1 , the CO 2 concentration in the chloroplast (C C ) can be calculated from simultaneous measurements of AN from gas exchange measurements, and the thylakoid electron flux from chlorophyll fluorometry. This permits diffusional effects (stomatal plus mesophyll limitations to CO 2 diffusion) to be differentiated from chloroplast-level effects. We used this method to investigate physiological restrictions to photosynthesis in leaves of water stressed cotton (Gossypium hirsutum L.) plants in a series of greenhouse experiments. A null-balance lysimeter was used to slowly induce four distinct levels of water stress. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments more effectively than gas exchange measurements alone. All treatments reduced C C , but only the two most severe stress treatments significantly increased nondiffusional restrictions, detectable as a reduction in the slope of AN on C C . In a second experiment, recovery of leaf photosynthesis was determined 24 and 48 h after relief of a severe stress by rewatering. Recovery of the A N /C C relationship was substantial but incomplete after 24 h and did not recover further by 48 h after rewatering, indicating lasting chloroplast-level injury as a result of the stress. Similar experiments should be conducted under field conditions to determine if water stress results in irreversible chloroplast-level injury in field-grown cotton.