Showing papers on "Photosynthesis published in 2000"
TL;DR: Results indicate that PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis, a finding that has implications for the functional evolution of pigment-binding proteins.
Abstract: Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules, thereby protecting the plant against photo-oxidative damage. To identify specific proteins that are involved in nonphotochemical quenching, we have isolated mutants of Arabidopsis thaliana that cannot dissipate excess absorbed light energy. Here we show that the gene encoding PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis. These results indicate that PsbS may be the site for nonphotochemical quenching, a finding that has implications for the functional evolution of pigment-binding proteins.
1,427 citations
TL;DR: This review considers photosynthesis as a whole-cell process, in which O2 and AOS are involved in reactions at both photosystems, enzyme regulation in the chloroplast stroma, photorespiration, and mitochondrial electron transport in the light, and oxidants and antioxidants are discussed as metabolic indicators of redox status, acting as sensors and signal molecules leading to acclimatory responses.
Abstract: summary The gradual but huge increase in atmospheric O # concentration that followed the evolution of oxygenic photosynthesis is one consequence that marks this event as one of the most significant in the earth’s history. The high redox potential of the O # }water couple makes it an extremely powerful electron sink that enables energy to be transduced in respiration. In addition to the tetravalent interconversion of O # and water, there exist a plethora of reactions that involve the partial reduction of O # or photodynamic energy transfer to produce active oxygen species (AOS). All these redox reactions have become integrated during evolution into the aerobic photosynthetic cell. This review considers photosynthesis as a whole-cell process, in which O # and AOS are involved in reactions at both photosystems, enzyme regulation in the chloroplast stroma, photorespiration, and mitochondrial electron transport in the light. In addition, oxidants and antioxidants are discussed as metabolic indicators of redox status, acting as sensors and signal molecules leading to acclimatory responses. Our aim throughout is to assess the insights gained from the application of mutagenesis and transformation techniques to studies of the role of O # and related redox components in the integrated regulation of photosynthesis.
809 citations
760 citations
TL;DR: The possible role of photorespiration under stress conditions, such as drought, high salt concentrations and high light intensities encountered by alpine plants, is discussed.
Abstract: Photorespiration results from the oxygenase reaction catalysed by ribulose–1,5–bisphosphate carboxylase/oxygenase. In this reaction glycollate–2–phosphate is produced and subsequently metabolized in the photorespiratory pathway to form the Calvin cycle intermediate glycerate–3–phosphate. During this metabolic process, CO2 and NH3 are produced and ATP and reducing equivalents are consumed, thus making photorespiration a wasteful process. However, precisely because of this inefficiency, photorespiration could serve as an energy sink preventing the overreduction of the photosynthetic electron transport chain and photoinhibition, especially under stress conditions that lead to reduced rates of photosynthetic CO2 assimilation. Furthermore, photorespiration provides metabolites for other metabolic processes, e.g. glycine for the synthesis of glutathione, which is also involved in stress protection. In this review, we describe the use of photorespiratory mutants to study the control and regulation of photorespiratory pathways. In addition, we discuss the possible role of photorespiration under stress conditions, such as drought, high salt concentrations and high light intensities encountered by alpine plants.
701 citations
TL;DR: In this article, selectable traits are discussed in the context of increasing total above-ground biomass under favorable conditions, and the importance of these traits will depend on the environment in which the crop is grown.
Abstract: The grain yield of cereals has almost doubled this century as a result of genetic manipulation by plant breeding. Surprisingly, there has been no change in the rate of photosynthesis per unit leaf area to accompany these increases. However, total photosynthesis has increased as a result of an increase in leaf area, daily duration of photosynthesis or leaf area duration. There remain substantial opportunities to continue to improve total photosynthesis and crop yield genetically using conventional breeding practices. Selectable traits are discussed here in the context of increasing total above-ground biomass under favourable conditions. Opportunities exist to alter crop duration and the timing of crop development to match it better to radiation, temperature and vapour pressure during crop growth, and to increase the rate of development of early leaf area to achieve rapid canopy closure. The importance of these traits will depend on the environment in which the crop is grown. Increases in crop photosynthesis through breeding are also likely to come via indirect means. Selection for a high and sustained stomatal conductance during the period of stem elongation is one way. Increasing assimilate allocation to the reproductive primordia so as to establish a large potential sink should also indirectly increase total crop photosynthesis. Evidence in the major grain crops suggests that by anthesis the capacity for photosynthesis is high and that photosynthesis is not limiting during grain filling. To use this surplus capacity it is suggested that carbon and nitrogen partitioning to the reproductive meristem be increased so as to establish a high potential grain number and the potential for a large grain size. It is then expected that additional photosynthesis will follow, either by a longer daily duration of photosynthesis or by an extended leaf area duration.
688 citations
TL;DR: The results indicate that, as temperature increases, the rate of Rubisco deactivation exceeds the capacity of activase to promote activation, and that this response was inconsistent with the response predicted from the properties of fully activated Rubisco.
Abstract: Net photosynthesis (Pn) is inhibited by moderate heat stress. To elucidate the mechanism of inhibition, we examined the effects of temperature on gas exchange and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation in cotton and tobacco leaves and compared the responses to those of the isolated enzymes. Depending on the CO2 concentration, Pn decreased when temperatures exceeded 35–40°C. This response was inconsistent with the response predicted from the properties of fully activated Rubisco. Rubisco deactivated in leaves when temperature was increased and also in response to high CO2 or low O2. The decrease in Rubisco activation occurred when leaf temperatures exceeded 35°C, whereas the activities of isolated activase and Rubisco were highest at 42°C and >50°C, respectively. In the absence of activase, isolated Rubisco deactivated under catalytic conditions and the rate of deactivation increased with temperature but not with CO2. The ability of activase to maintain or promote Rubisco activation in vitro also decreased with temperature but was not affected by CO2. Increasing the activase/Rubisco ratio reduced Rubisco deactivation at higher temperatures. The results indicate that, as temperature increases, the rate of Rubisco deactivation exceeds the capacity of activase to promote activation. The decrease in Rubisco activation that occurred in leaves at high CO2 was not caused by a faster rate of deactivation, but by reduced activase activity possibly in response to unfavorable ATP/ADP ratios. When adjustments were made for changes in activation state, the kinetic properties of Rubisco predicted the response of Pn at high temperature and CO2.
652 citations
TL;DR: The water-water cycle in chloroplasts is the photoreduction of dioxygen to water in photosystem I (PS I) by the electrons generated in photoystem II (PS II) from water.
Abstract: The waterwater cycle in chloroplasts is the photoreduction of dioxygen to water in photosystem I (PS I) by the electrons generated in photosystem II (PS II) from water. In the waterwater cycle, the...
547 citations
TL;DR: Phylogenetic analyses of multiple magnesium-tetrapyrrole biosynthesis genes using a combination of distance, maximum parsimony, and maximum likelihood methods indicate that heliobacteria are closest to the last common ancestor of all oxygenic photosynthetic lineages and that green sulfur bacteria and green nonsulfur bacteria are each other's closest relatives.
Abstract: The origin and evolution of photosynthesis have long remained enigmatic due to a lack of sequence information of photosynthesis genes across the entire photosynthetic domain. To probe early evolutionary history of photosynthesis, we obtained new sequence information of a number of photosynthesis genes from the green sulfur bacterium Chlorobium tepidum and the green nonsulfur bacterium Chloroflexus aurantiacus. A total of 31 open reading frames that encode enzymes involved in bacteriochlorophyll/porphyrin biosynthesis, carotenoid biosynthesis, and photosynthetic electron transfer were identified in about 100 kilobase pairs of genomic sequence. Phylogenetic analyses of multiple magnesium-tetrapyrrole biosynthesis genes using a combination of distance, maximum parsimony, and maximum likelihood methods indicate that heliobacteria are closest to the last common ancestor of all oxygenic photosynthetic lineages and that green sulfur bacteria and green nonsulfur bacteria are each other's closest relatives. Parsimony and distance analyses further identify purple bacteria as the earliest emerging photosynthetic lineage. These results challenge previous conclusions based on 16S ribosomal RNA and Hsp60/Hsp70 analyses that green nonsulfur bacteria or heliobacteria are the earliest phototrophs. The overall consensus of our phylogenetic analysis, that bacteriochlorophyll biosynthesis evolved before chlorophyll biosynthesis, also argues against the long-held Granick hypothesis.
467 citations
Book•
01 Jan 2000
TL;DR: This chapter discusses thephysiology of Plants with Crassulacean Acid Metabolism with a focus on C4 Photosynthesis and the role of carbonic Anhydrase in this process.
Abstract: Preface. Color Plates. 1. Introduction R.C. Leegood, et al. 2. The Calvin Cycle and Its Regulation W. Martin, et al. 3. Rubisco: Assembly and Mechanism H. Roy, T.J. Andrews. 4. Rubisco: Physiology in Vivo S. von Caemmerer, W.P. Quick. 5. Photorespiration R. Douce, H.-W. Heldt. 6. Metabolite Transport Across the Chloroplast Envelope of C3-Plants U.-I. Flugge. 7. Photosynthesis, Carbohydrate Metabolism and Respiration in Leaves of Higher Plants O.K. Atkin, et al. 8. Regulation of Carbon Fluxes in the Cytosol: Coordination of Sucrose Synthesis, Nitrate Reduction and Organic Acid and Amino Acid Biosynthesis C.H. Foyer, et al. 9. Starch Metabolism in Leaves R.N. Trethewey, A.M. Smith. 10. Control of Photosynthesis, Allocation and Partitioning by Sugar Regulated Gene Expression I.A. Graham, T. Martin. 11. Intercellular Transport and Phloem Loading of Sucrose, Oligosaccharides and Amino Acids C. Schobert, et al. 12. Regulation of Sugar Alcohol Biosynthesis W.H. Loescher, J.D. Everard. 13. Fructans: Synthesis and Regulation A.J. Cairns, et al. 14. Acquisition and Diffusion of CO2 in Higher Plant Leaves J.R. Evans, F. Loreto. 15. Carbonic Anhydrase and Its Role in Photosynthesis J.R. Coleman. 16. CO2 Acquisition, Concentration and Fixation in Cyanobacteria and Algae M.R. Badger, M.H. Spalding. 17. Photosynthetic Fractionation of Carbon Isotopes E. Brugnoli, G.D. Farquhar. 18. C4Photosynthesis: Mechanism and Regulation R.T. Furbank, et al. 19. Transport During C4 Photosynthesis R.C. Leegood. 20. Developmental Aspects of C4 Photosynthesis N.G. Dengler, W.C. Taylor. 21. The Physiological Ecology of C4 Photosynthesis R.F. Sage, R.W. Pearcy. 22. CO2 Assimilation in C3-C4 Intermediate Plants R.K. Monson, S. Rawsthorne. 23. Induction of Crassulacean Acid Metabolism -- Molecular Aspects J.C. Cushman, et al. 24. Ecophysiology of Plants with Crassulacean Acid Metabolism A.M. Borland, et al. Index.
377 citations
TL;DR: A number of recent and past studies with higher plants, algae and cyanobacteria that have attempted to quantify O2 fluxes under various conditions and their contributions to a number of roles, including photon energy dissipation are reviewed.
Abstract: Linear electron transport in chloroplasts produces a number of reduced components associated with photosystem I (PS I) that may subsequently participate in reactions that reduce O2. The two primary reactions that have been extensively studied are: first, the direct reduction of O2 to superoxide by reduced donors associated with PS I (the Mehler reaction), and second, the rubisco oxygenase (ribulose 1,5-bisphosphate carboxylase oxygenase EC 4.1.1.39) reaction and associated peroxisomal and mitochondrial reactions of the photorespiratory pathway. This paper reviews a number of recent and past studies with higher plants, algae and cyanobacteria that have attempted to quantify O2 fluxes under various conditions and their contributions to a number of roles, including photon energy dissipation. In C3 and Crassulacean acid metabolism (CAM) plants, a Mehler O2 uptake reaction is unlikely to support a significant flow of electron transport (probably less than 10%). In addition, if it were present it would appear to scale with photosynthetic carbon oxidation cycle (PCO) and photosynthetic carbon reduction cycle (PCR) activity This is supported by studies with antisense tobacco plants with reduced rubisco at low and high temperatures and high light, as well as studies with potatoes, grapes and madrone during water stress. The lack of significant Mehler in these plants directly argues for a strong control of Mehler reaction in the absence of ATP consumption by the PCR and PCO cycles. The difference between C3 and C4 plants is primarily that the level of light-dependent O2 uptake is generally much lower in C4 plants and is relatively insensitive to the external CO2 concentration. Such a major difference is readily attributed to the operation of the C4 CO2 concentrating mechanism. Algae show a range of light-dependent O2 uptake rates, similar to C4 plants. As in C4 plants, the O2 uptake appears to be largely insensitive to CO2, even in species that lack a CO2 concentrating mechanism and under conditions that are clearly limiting with respect to inorganic carbon supply. A part explanation for this could be that many algal rubsicos have considerably different oxygenase kinetic properties and exhibit far less oxygenase activity in air. This would lead to the conclusion that perhaps a greater proportion of the observed O2 uptake may be due to a Mehler reaction and less to rubisco, compared with C3 plants. In contrast to algae and higher plants, cyanobacteria appear to have a high capacity for Mehler O2 uptake, which appears to be not well coupled or limited by ATP consumption. It is likely that in all higher plants and algae, which have a well-developed non-photochemical quenching mechanism, non-radiative energy dissipation is the major mechanism for dissipating excess photons absorbed by the light-harvesting complexes under stressful conditions. However, for cyanobacteria, with a lack of significant non-photochemical quenching, the situation may well be different.
358 citations
01 Jan 2000
TL;DR: In this paper, the application of carbon isotope discrimination to physiological and ecophysiological studies and to selection of genotypes with improved water-use efficiency and drought tolerance is reviewed.
Abstract: During photosynthetic CO2 fixation fractionation of stable carbon isotopes occurs and, consequently, plants are generally depleted in the heavier isotope 13C. Carbon isotope discrimination (Δ) is a measure of this process and depends on fractionation during diffusion and during enzymatic carboxylation reactions. Discrimination during photosynthesis has a significant, though relatively small, effect on the isotopic composition of atmospheric CO2 both at regional and global level; hence stable isotopes find relevant applications in the study of the global carbon cycle. In addition to variation in Δ among plants with different photosynthetic pathways, large variations are found within plant groups, resulting from genetic and environmental influences on the ratio of partial pressures of CO2 at the sites of carboxylation and that in the free turbulent atmosphere. Experimental evidences confirming the theory of carbon isotope discrimination and known complications are discussed. Carbon isotope composition also varies among different metabolites, compartments and plant organs as a result of fractionation during secondary metabolism and variation in the ratio of diffusional and carboxylation limitations. Special emphases are given to measurements of Δ in different carbon pools such as bulk dry matter, cellulose, starch and sucrose, with different turnover rates and different integration of p1/p8 and to the links with water-use efficiency. The application of carbon isotope discrimination to physiological and ecophysiological studies and to selection of genotypes with improved water-use efficiency and drought tolerance and the recent progress in this field are reviewed.
TL;DR: It is predicted that increasing UV-B due to future stratospheric ozone depletion is unlikely to have any significant impact on the photosynthetic productivity of olive, lavender and rosemary in the field.
Abstract: The effects of drought on the photosynthetic characteristics of three Mediterranean plants (olive, Olea europea L.; rosemary, Rosmarinus officinalis L.; lavender, Lavandula stoechas L.) exposed to elevated UV-B irradiation in a glasshouse were investigated over a period of weeks. Drought conditions were imposed on 2-year-old plants by withholding water. During the onset of water stress, analyses of the response of net carbon assimilation of leaves to their intercellular CO2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bisphosphate on photosynthesis. Measurements of chlorophyll fluorescence were used to determine changes in the efficiency of light utilization for electron transport, the occurrence of photoinhibition of photosystem II photochemistry and the possibility of stomatal patchiness across leaves. The first stages of water stress produced decreases in the light-saturated rate of CO2 assimilation which were accompanied by decreases in the maximum carboxylation velocity and the capacity for regeneration of ribulose 1,5-bisphosphate in the absence of any significant photodamage to photosystem II. Leaves of rosemary and lavender were more sensitive than those of olive during the first stages of the drought treatment and also exhibited increases in stomatal limitation. With increasing water stress, significant decreases in the maximum quantum efficiency of photosystem II photochemistry occurred in lavender and rosemary, and stomatal limitation was increased in olive. No indication of any heterogeneity of photosynthesis was found in any leaves. Drought treatment significantly decreased leaf area in all species, an important factor in drought-induced decreases in photosynthetic productivity. Exposure of plants to elevated UV-B radiation (0.47 W m(-2)) prior to and during the drought treatment had no significant effects on the growth or photosynthetic activities of the plants. Consequently, it is predicted that increasing UV-B due to future stratospheric ozone depletion is unlikely to have any significant impact on the photosynthetic productivity of olive, lavender and rosemary in the field.
TL;DR: Investigation of ascorbate-deficient Arabidopsis thaliana vtc mutants shows that they have reduced zeaxanthin-dependent non-photochemical quenching, confirming that asCorbate is the cofactor for violaxanth in de-epoxidase and that availability of thylakoid lumen ascorBate could limit this reaction.
Abstract: Ascorbate (vitamin C) can reach very high concentrations in chloroplasts (20-300 mM). The pool size in leaves and chloroplasts increases during acclimation to high light intensity and the highest concentrations recorded are in high alpine plants. Multiple functions for ascorbate in photosynthesis have been proposed, including scavenging of active oxygen species generated by oxygen photoreduction and photorespiration, regeneration of alpha-tocopherol from alpha-tocopheryl radicals, cofactor for violaxanthin de-epoxidase and donation of electrons to photosystem II. Hydrogen peroxide scavenging is catalysed by ascorbate peroxidase (Mehler peroxidase reaction) and the subsequent regeneration of ascorbate by reductant derived from photosystem I allows electron flow in addition to that used for CO2 assimilation. Ascorbate is synthesized from guanosine diphosphate-mannose via L-galactose and L-galactono-1,4-lactone. The last step, catalysed by L-galactono-1,4-lactone dehydrogenase, is located on the inner mitochondrial membrane and uses cytochrome c as electron acceptor. L-galactono-1,4-lactone oxidation to ascorbate by intact leaves is faster in high-light acclimated leaves and is also enhanced by high light, suggesting that this step contributes to the control of pool size by light. Ascorbate-deficient Arabidopsis thaliana vtc mutants are hypersensitive to a number of oxidative stresses including ozone and ultraviolet B radiation. Further investigation of these mutants shows that they have reduced zeaxanthin-dependent non-photochemical quenching, confirming that ascorbate is the cofactor for violaxanthin de-epoxidase and that availability of thylakoid lumen ascorbate could limit this reaction. The vtc mutants are also more sensitive to photo-oxidation imposed by combined high light and salt treatments.
TL;DR: Evidence is presented that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms.
Abstract: Nearly 50 years ago, inorganic carbon was shown to be fixed in microalgae as the C3 compound phosphoglyceric acid. The enzyme responsible for C3 carbon fixation, ribulose-1,5-bisphosphate carboxylase (Rubisco), however, requires inorganic carbon in the form of CO2 (ref. 2), and Rubisco enzymes from diatoms have half-saturation constants for CO2 of 30-60 microM (ref. 3). As a result, diatoms growing in seawater that contains about 10 microM CO2 may be CO2 limited. Kinetic and growth studies have shown that diatoms can avoid CO2 limitation, but the biochemistry of the underlying mechanisms remains unknown. Here we present evidence that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms. If C4 photosynthesis is common among marine diatoms, it may account for a significant portion of carbon fixation and export in the ocean, and would explain the greater enrichment of 13C in diatoms compared with other classes of phytoplankton. Unicellular C4 carbon assimilation may have predated the appearance of multicellular C4 plants.
TL;DR: The first biophysical evidence demonstrating that aerobic bacterial photosynthesis is widespread is reported, indicating that these organisms account for 2–5% of the photosynthetic electron transport in the upper ocean.
Abstract: The oxidation of the global ocean by cyanobacterial oxygenic photosynthesis, about 2,100 Myr ago, is presumed to have limited anoxygenic bacterial photosynthesis to oceanic regions that are both anoxic and illuminated. The discovery of oxygen-requiring photosynthetic bacteria about 20 years ago changed this notion, indicating that anoxygenic bacterial photosynthesis could persist under oxidizing conditions. However, the distribution of aerobic photosynthetic bacteria in the world oceans, their photosynthetic competence and their relationship to oxygenic photoautotrophs on global scales are unknown. Here we report the first biophysical evidence demonstrating that aerobic bacterial photosynthesis is widespread in tropical surface waters of the eastern Pacific Ocean and in temperate coastal waters of the northwestern Atlantic. Our results indicate that these organisms account for 2-5% of the photosynthetic electron transport in the upper ocean.
TL;DR: It is suggested that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems.
Abstract: We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI = (maximum value - minimum)/maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems.
TL;DR: The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions and the photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition.
TL;DR: Phytoplankton respond to variations in light intensity as they are mixed through the water column to modulate the rate of photosynthesis in situ, which influences light harvesting and Calvin cycle activity.
TL;DR: Little is known about the physiological ecology of seagrasses in carbon acquisition and metabolism, but the role of carbon metabolism in salt tolerance, growth under resource-limited conditions, and survival through periods of dormancy - remain to be resolved as directions in future research.
TL;DR: In this paper, the responses of photosynthetic gas exchange and Chi fluorescence to nitrogen nutrition were studied under well-watered and drought conditions in winter wheat leaves, and the results showed that nitrogen deficiency and water deficit strongly reduced the photosynthesis activity at light saturation level.
TL;DR: The above findings suggest that the increase in GB content is important in adaptation to salt stress in Amaranthus plants, although photosynthesis and transpiration responses occurred immediately after salt-stress.
Abstract: SummaryWe examined changes in leaf growth and chemical composition, including chlorophyll content, ribulose bisphosphate carboxylase-oxygenase (RuBisCO), and glycine betaine (GB) in relation to photosynthesis and transpiration responses to salt stress in Amaranthus tricolor leaves. To induce salt stress, plants were transferred to a growth medium containing 300 mM NaCl for 7 d followed by 7 d of relief from salinity. A decrease in leaf enlargement began 3 d after salt stress, and leaves subsequently showed the same degree of regrowth as controls after relief in non-salt medium. Chlorophyll content expressed on a leaf-area basis increased under conditions of salinity due to a reduction in leaf tissue water content. The decrease in chlorophyll content continued throughout the 7 d of relief from salinity. The RuBisCO and soluble protein contents when expressed on a leaf dry-weight basis decreased in response to salinity, and then gradually increased during the relief period. GB content increased slightly up ...
TL;DR: The results indicate that trienoic fatty acids are important to ensure the correct biogenesis and maintenance of chloroplasts during growth of plants at low temperatures.
Abstract: The chloroplast membranes of all higher plants contain very high proportions of trienoic fatty acids. To investigate how these lipid structures are important in photosynthesis, we have generated a triple mutant line of Arabidopsis that contains negligible levels of trienoic fatty acids. For mutant plants grown at 22°C, photosynthetic fluorescence parameters were indistinguishable from wild type at 25°C. Lowering the measurement temperature led to a small decrease in photosynthetic quantum yield, Φ II , in the mutant relative to wild-type controls. These and other results indicate that low temperature has only a small effect on photosynthesis in the short term. However, long-term growth of plants at 4°C resulted in decreases in fluorescence parameters, chlorophyll content, and thylakoid membrane content in triple-mutant plants relative to wild type. Comparisons among different mutant lines indicated that these detrimental effects of growth at 4°C are strongly correlated with trienoic fatty acid content with levels of 16:3 + 18:3, approximately one-third of wild type being sufficient to sustain normal photosynthetic function. In total, our results indicate that trienoic fatty acids are important to ensure the correct biogenesis and maintenance of chloroplasts during growth of plants at low temperatures.
TL;DR: Results argue against the importance of exogenous organic carbon supply as a significant energy source to freshwater planktonic communities in oligotrophic to mesotrophic Shield lakes.
Abstract: A precise oxygen method was used to measure primary production, community respiration and to determine the importance of exogenous organic carbon as an energy source to planktonic communities in the epilimnion of 12 oligotrophic to mesotrophic Shield lakes. Median photosynthetic parameters observed with the oxygen method were up to twice as high as those measured with 14 C in other oligotrophic Shield lakes. Gross photosynthesis was almost always larger than community respiration, with a median P : R ratio of 1.7. We observed strong relationships between respiration and gross photosynthesis, but could not detect any significant trend between respiration or the P : R ratio and the concentration of dissolved organic carbon (DOC). DOC appeared to depress both photosynthesis and respiration. These results argue against the importance of exogenous organic carbon supply as a significant energy source to freshwater planktonic communities. Previously low P : R ratios reported for oligotrophic fresh waters may be due to the uncertain meaning of 14 C production data.
TL;DR: Differences of photosynthesis versus irradiance curves between cells acclimated to high-light versus low-light could be accounted for largely in terms of changes in cell chlorophyll a contents, which may indicate that control of light-saturated photosynthesis shifts from enzymes of the carbon dioxide reduction cycle in low-lights to the photosynthetic electron transfer chain in high-lights.
Abstract: Photoacclimation was examined in the marine diatom Skeletonema costatum, which was subjected to reciprocal shifts between irradiances of 50 (low-light) and 1,200 (high-light) mmol photons m 22 s 21 . Cell chlorophyll a and fucoxanthin contents were higher but diadinoxanthin and diatoxanthin contents lower in cells grown at 50 mmol photons m 22 s 21 than in cells shifted to 1200 mmol photons m 22 s 21 . Cell carbon contents measured at the start of the light period were similar in both high-light and low-light treatments. However, b y 6 h into the light period, the carbon contents in the high-light cells were about twofold higher than in the low-light cells. Dark respiration rates, dark Chl a synthesis rates, and dark cell-division rates were greater in the high-light acclimated cells than in the low-light cells. Thus, there was a greater uncoupling of carbon assimilation from cell division during the day in the high-light cells, but pigment synthesis and cell division continued in darkness. Cell-specific, light saturated photosynthesis rates, and chlorophyll a specific light-limited photosynthesis rates were constant during reciprocal shifts between growth irradiances of 50 and 1200 mmol photons m 22 s 21 . Thus, differences of photosynthesis versus irradiance curves between cells acclimated to high-light versus low-light could be accounted for largely in terms of changes in cell chlorophyll a contents. Although the chlorophyll a-specific initial slope, a chl , was constant, the chlorophyll a-specific light absorbtion coeffecient, a chl , increased and the maximum quantum efficiency of photosynthesis (fm) declined following the shift to high light. The increase of a chl was most likely due to a decreased package effect. The decline of fm was most likely due to accumulation of xanthophyll cycle pigments. Carbonspecific, light-saturated photosynthesis rates were lower in high-light than in low-light cells; this observation may indicate that control of light-saturated photosynthesis shifts from enzymes of the carbon dioxide reduction cycle (Calvin cycle) in low-light cells to the photosynthetic electron transfer chain in high-light cells.
Book•
01 Jul 2000
TL;DR: The chloroplast structure and development, metabolism and regulation of plastid genes, and application in biotechnology are studied.
Abstract: Part I. Cell and Molecular Biology of Chloroplasts: 1. Chloroplast structure and development J. K. Hoober 2. Light harvesting complexes of higher plants D. T. Morishige and B. W. Dreyfuss 3. Photosystems I and II W.-Z. He and R. Malkin 4. Chloroplast pigments: chlorophylls and carotenoids G. Sandmann and H. Scheer 5. Import, assembly and degradation of proteins P. Chitnis 6. Expression and regulation of plastid genes S. Kapoor and M. Sugiura 7. Electron transport and energy transduction W. Junge Part II. Physiology and Biochemistry: 8. Photosynthetic carbon reduction T. D. Sharkey 9. C4 pathway R. T. Furbank 10. Crassulacean acid metabolism U. Luttge 11. C3-C4 intermediate photosynthesis S. Rawsthorne and H. Bauwe 12. Starch-sucrose metabolism and assimilate partitioning S. C. Hoober 13. Photorespiration and the C2 cycle D. J. Oliver 14. Assimilation of non-carbohydrate compounds G. Schultz 15. Interaction with respiration and nitrogen metabolism K. Padmasree and A. S. Raghavendra Part III. Agronomy and Environmental Factors: 16. Leaf/canopy photosynthesis and crop productivity R. Ishii 17. Water and salt stress G. A. Berkowitz 18. Photosynthesis at low growth temperature V. Hurry, N. Huner, E. Selstam, P. Gardestrom and G. Oquist 19. Acclimation to sun and shade R. W. Pearcy 20. Photoinhibition C. Critchley 21. Photosynthesis, respiration and global climatic change B. G. Drake, J. Jacob and M. A. Gonzales-Meler Part IV. Special Topics and Applications: 22. Evolution W. Nitschke, U. Muhlenhoff and U. Liebl 23. Modelling leaf/canopy photosynthesis W. R. Beyschlag and R. J. Ryel 24. Chlorophyll fluorescence as a diagnostic tool U. Schreiber, W. Bilger, H. Hormann and C. Neubauer 25. Action of modern herbicides P. Boger and G. Sandmann 26. Application in biotechnology D. Heineke Index.
TL;DR: Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen during a 72-h exposure to UV radiation, finding that different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field.
Abstract: Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen (Monostroma arcticum, Laminaria solidungula, Alaria esculenta, Palmaria palmata, Phycodrys rubens) during a 72-h exposure to UV radiation. Maximal quantum yield of photochemistry (Fv/Fm) and maximal electron transport rate (ETRmax) were measured with a pulse-amplitude-modulated fluorometer; the activity of the Calvin cycle enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric test. Proteins of crude extracts were separated by SDS gel electrophoresis and changes in cellular concentrations of Rubisco were determined. Moreover, the concentration of chlorophyll a (Chl a), and protein content, were measured photometrically. In all species, Chl a content, maximal quantum yield as well as ETRmax decreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gels showed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradation of the enzyme. However, in A. esculenta, the formation of a high-molecular-weight polypeptide was observed. In all species, the activity of Rubisco was more strongly impaired than that of G3PDH. Exposure to UV resulted in loss of total protein only in the deepwater species L. solidungula and P. rubens. The different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field.
TL;DR: It is concluded that low phosphate plays an important role in triggering cold acclimatization of leaves, leading in particular to an increase of Rubisco expression, changes in other Calvin cycle enzymes to minimize sequestration of phosphate in metabolites, and increased expression of sucrose biosynthesis enzymes.
Abstract: Summary
Low temperature inhibits sucrose synthesis, leading to a phosphate-limitation of photosynthesis. We have used the Arabidopsis pho1-2 and pho2-1 mutants with decreased and increased shoot phosphate, respectively, to investigate whether low phosphate triggers cold acclimatization of photosynthetic carbon metabolism. Wild-type Arabidopsis, pho1-2 and pho2-1 were grown at 23°C and transferred to 5°C to investigate acclimatization in pre-existing leaves and in new leaves developing at 5°C. The development of frost tolerance and the accumulation of proline and sugars was unaltered or improved in pho1-2, and impaired in pho2-1. Sucrose phosphate synthase and cytoplasmic fructose-1,6-bisphosphatase activity and protein increase after transfer to 5°C. This increase was accentuated in pho1-2 and attenuated in pho2-1. RBCS and LHCB2 transcript levels decrease in pre-formed wild-type leaves after transfer to 5°C and recover in new leaves that develop at 5°C. The initial decrease was attenuated in pho1-2, and accentuated in pho2-1, where the recovery in new leaves was also suppressed. Rubisco activity increased in wild-type leaves that developed at 5°C. This increase was accentuated in pho1-2 and absent in pho2-1. NADP-glyceraldehyde-3-phosphate dehydrogenase, plastidic fructose-1,6-bisphosphatase and aldolase activity increase relative to phosphoglycerate kinase, transketolase and phosphoribulokinase in wild-type leaves at 5°C. This shift was accentuated in pho1-2 and reversed in pho2-1. Transcript levels for COR genes increase transiently 1 day after transfer to 5°C but were very low in leaves that developed at 5°C in wild-type Arabidopsis, pho1-2 and pho2-1. We conclude that low phosphate plays an important role in triggering cold acclimatization of leaves, leading in particular to an increase of Rubisco expression, changes in other Calvin cycle enzymes to minimize sequestration of phosphate in metabolites, and increased expression of sucrose biosynthesis enzymes.
TL;DR: In this salt-sensitive genotype, both photosynthesis and growth were negatively correlated with fructose, glucose and sucrose accumulation in both mature and young leaves, suggesting a blockage in their use for growth.
Abstract: The different growth responses under salinity in relation to the carbon partitioning and sucrose metabolism in both sink and source organs have been studied in a salt-tolerant (cv. Pera) and in a salt-sensitive (cv. Volgogradskij) tomato genotype (Lycopersicon esculentum Mill.). After 3 weeks of salinization, the plant dry weight was reduced by 12-34% in cv. Pera and by 45-58% in cv. Volgogradskij. Photosynthesis was positively correlated to plant growth in cv. Pera but not in cv. Volgogradskij. In this salt-sensitive genotype, both photosynthesis and growth were negatively correlated with fructose, glucose and sucrose accumulation in both mature and young leaves, suggesting a blockage in their use for growth. The transient accumulation of sucrose and hexoses in the young leaves of cv. Pera was linked to increases in all soluble sucrolytic activities, mainly acid invertase (EC 3.2.1.25) and sucrose synthase (EC 2.4.1.13), which was related to sink activity and growth capacity. The sucrose-phosphate synthase activity (EC 2.4.1.14) was related to the ability of mature leaves to regulate assimilate production, accumulation and export. The salt-tolerant cv. Pera accumulated a higher amount of total carbohydrates, but cv. Volgogradskij showed the highest soluble fraction under salinity. The carbohydrate availability and the photosynthetic rate do not seem to be the first limiting factors for plant growth under saline conditions, but the different behavior observed in both genotypes concerning the distribution and use of photoassimilates could help to explain their different salt-tolerance degrees.
TL;DR: The particular absorptive characteristics of chlorophylls a and b appear to perform two contradictory, but necessary functions in higher plants, which may have been the selective force that gave rise to the extremely successful terrestrial plants, that evolved from green algae.
Abstract: The physiological reason that higher plants are green is unknown. Other photosynthetic organisms utilize pigments that strongly absorb green light; therefore, there must have been natural forces that ‘selected’ the photosynthetic pigments found in higher plants. Based on previously published data and our recent findings about green light and photosynthesis within leaves (Sun et al.), a specific functional role is described for the primary photosynthetic pigments of higher plants, that were derived from green algal progenitors. The particular absorptive characteristics of chlorophylls a and b appear to perform two contradictory, but necessary functions in higher plants. Firstly, chlorophylls a and b absorb light for maximum utilization under non-saturating conditions, a function that is well understood. Secondly, they can act as protective pigments under over-saturating light conditions, when absorbed light is dissipated as heat. Under such conditions, a significant portion of light can also be efficiently utilized, especially in the bottom portion of the leaf, that is mainly illuminated by green light and not down-regulated. The second function may have been the selective force that gave rise to the extremely successful terrestrial plants, that evolved from green algae.
TL;DR: Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco plants showing delayed leaf senescence through a novel type of enhanced cytokinIn synthesis, targeted to senescing leaves and negatively auto-regulated (PSAG12‐IPT), thus preventing developmental abnormalities.
Abstract: We studied the impact of delayed leaf senescence on the functioning of plants growing under conditions of nitrogen remobilization. Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco (Nicotiana tabacum L.) plants showing delayed leaf senescence through a novel type of enhanced cytokinin synthesis, i.e. targeted to senescing leaves and negatively auto-regulated (PSAG12‐IPT), thus preventing developmental abnormalities. Plants were grown with growthlimiting nitrogen supply. Compared to the wild-type, endogenous levels of free zeatin (Z)- and Z riboside (ZR)type cytokinins were increased up to 15-fold (total ZR up to 100-fold) in senescing leaves, and twofold in younger leaves of PSAG12‐IPT. In these plants, the senescenceassociated declines in N, protein and Rubisco levels and photosynthesis rates were delayed. Senescing leaves accumulated more ( 15 N-labelled) N than younger leaves, associated with reduced shoot N accumulation (‐60%) and a partially inverted canopy N profile in PSAG12‐IPT plants. While root N accumulation was not affected, N translocation to non-senescing leaves was progressively reduced. We discuss potential consequences of these modified sink‐source relations, associated with delayed leaf senescence, for plant productivity and the efficiency of utilization of light and minerals.