Showing papers on "Photosynthesis published in 1987"

Photoinhibition and zeaxanthin formation in intact leaves : a possible role of the xanthophyll cycle in the dissipation of excess light energy.

Abstract: Comparative studies of chlorophyll a fluorescence, measured with a pulse amplitude modulated fluorometer, and of the pigment composition of leaves, suggest a specific role of zeaxanthin, a carotenoid formed in the xanthophyll cycle, in protecting the photosynthetic apparatus against the adverse effects of excessive light. This conclusion is based on the following findings: (a) exposure of leaves of Populus balsamifera, Hedera helix, and Monstera deliciosa to excess excitation energy (high light, air; weak light, 2% O2, 0% CO2) led to massive formation of zeaxanthin and a decrease in violaxanthin. Over a wide range of conditions, there was a linear relationship between either variable, Fv, or maximum fluorescence, Fm, and the zeaxanthin content of leaves. (b) When exposed to photoinhibitory light levels in air, shade leaves of H. helix had a higher capacity for zeaxanthin formation, at the expense of β-carotene, than shade leaves of M. deliciosa. Changes in fluorescence characteristics suggested that, in H. helix, the predominant response to high light was an increase in the rate of nonradiative energy dissipation, whereas, in M. deliciosa, photoinhibitory damage to photosystem II reaction centers was the prevailing effect. (c) Exposure of a sun leaf of P. balsamifera to increasing photon flux densities in 2% O2 and 0% CO2 resulted initially in increasing levels of zeaxanthin (matched by decreases in violaxanthin) and was accompanied by fluorescence changes indicative of increased nonradiative energy dissipation. Above the light level at which no further increase in zeaxanthin content was observed, fluorescence characteristics indicated photoinhibitory damage. (d) A linear relationship was obtained between the ratio of variable to maximum fluorescence, Fv/Fm, determined with the modulated fluorescence technique at room temperature, and the photon yield of O2 evolution, similar to previous findings (O Bjorkman, B Demmig 1987 Planta 170: 489-504) on chlorophyll fluorescence characteristics at 77 K and the photon yield of photosynthesis.

The light-harvesting and protective functions of carotenoids in photosynthetic membranes

Abstract: Siefermann-Harms, D. 1987. The light-harvesting and protective functions of carotenoids in photosynthetic membranes.

Temperature effects on photosynthetic capacity, respiration, and growth rates of bloom-forming cyanobacteria

Abstract: The literature was reviewed to determine the direct temperature effects on photosynthetic capacity (Pmax), specific respiration rate (Rest), and growth rate of bloom‐forming cyanobacteria (Anabaena, Aphanizomenon, Microcystis, Oscillatoria) and to assess the importance of direct tern‐perature effects on cyanobacterial dominance in lakes. This analysis is supported by field studies of Microcystis aeruginosa in a hypertrophic lake. The literature and field data show that Pmax, Rest, and growth rate are temperature‐dependent with optima usually at 25 °C or greater. The four genera varied in their response to low temperatures with Microcystis being most severely limited belw about 15 °C. Oscillatoria tended to tolerate the widest range of temperatures. However, an examination of field data from representative lakes around the world indicated that direct temperature effects were secondary to indirect temperature effects (mixing) and nutrients in determining the dominance of bloom‐forming cyanobacteria...

Effects of water deficit on photosynthetic capacity

Abstract: Under drought, CO2 assimilation rates decrease already at small leaf water deficits. At least part of the inhibition is attributed to non-stomata1 effects at the chloroplast level, with electron transport and phosphorylation being main targets of inhibition. These findings are questioned by direct measurements of photosynthetic capacity with systems that are not Limited by stomata, e.g. leaf slices in solution or leaves at ex-ternal CO2 concentrations exceeding 5%. Here, photosynthesis was rather insensitive to dehydration down to 50–70% relative water content, and different plant species re-sponded in a very similar way. More severe dehydration affected not only pboto-synthesis, but also dark CO2 fixation and presumably also photorespiration. Rever-sible and unspecific inhibition is thought to be mediated mainly by increased concen-trations of solutes in dehydrated cells. Inhibition of photorespiration might favour photoinhibition when long-term water stress is coupled with full sunlight. Photo-inhibition, together with general senescence phenomena might be involved in long-term effects of water stress under natural drought conditions. This offers an explanation for the conflicting results of short-term water stress experiments and studies carried out under field conditions.

Chilling-enhanced photooxidation : evidence for the role of singlet oxygen and superoxide in the breakdown of pigments and endogenous antioxidants.

Abstract: Chilling temperatures (5°C) and high irradiance (1000 microeinsteins per square meter per second) were used to induce photooxidation in detached leaves of cucumber (Cucumis sativus L.), a chilling-sensitive plant. Chlorophyll a, chlorophyll b, β carotene, and three xanthophylls were degraded in a light-dependent fashion at essentially the same rate. Lipid peroxidation (measured as ethane evolution) showed an O2 dependency. The levels of three endogenous antioxidants, ascorbate, reduced glutathione, and α tocopherol, all showed an irradiance-dependent decline. α-Tocopherol was the first antioxidant affected and appeared to be the only antioxidant that could be implicated in long-term protection of the photosynthetic pigments. Results from the application of antioxidants having relative selectivity for 1O2, O2−, or OH indicated that both 1O2 and O2− were involved in the chilling- and light-induced lipid peroxidation which accompanied photooxidation. Application of D2O (which enhances the lifetime of 1O2) corroborated these results. Chilling under high light produced no evidence of photooxidative damage in detached leaves of chilling-resistant pea (Pisum sativum L.). Our results suggest a fundamental difference in the ability of pea to reduce the destructive effects of free-radical and 1O2 production in chloroplasts during chilling in high light.

Mechanism of toxicity of ionic copper and copper complexes to algae

Abstract: The mechanism of toxicity of ionic copper and copper complexes to growth, photosynthesis, respiration, ATP levels and mitochondrial electron-transport chain-activity in two marine diatoms, Nitzschia closterium (Ehrenberg) W. Smith (Hasle, 1964) and Asterionella glacialis Castracane, and one freshwater green alga, Chlorella pyrenoidosa Chick was investigated. Copper ions depressed both cell division and photosynthesis in A. glacialis and C. pyrenoidosa, whereas ionic copper concentrations which were inhibitory to cell division in N. closterium had no effect on photosynthesis, respiration, ATP production, electron transport or membrane ultrastructure. This suggests that in N. closterium, copper does not act on the chloroplast, the mitochondrion, or the cell membrane, since if it did, the above parameters should be affected. Copper-ethylxanthogenate was exceptional amongst the copper complexes in that it stimulated respiration, mitochondrial electrontransport and ATP formation in N. closterium under conditions of strongly inhibited cell division and slightly stimulated photosynthesis. Ionic copper toxicity may result from an intracellular reaction between copper and reduced glutathione (GSH), leading to a lowering of the GSH:GSSG ratio and suppression of mitosis. In addition, copper inhibits the enzyme catalase and reduces cell defence mechanisms against H2O2 and oxygen-free radicals. Lipid-soluble copper complexes are more toxic than ionic copper because both the metal and the ligand are introduced into the cell. Toxicity of ionic copper is ameliorated by trivalent metal ions in the growth medium, including those of Mn, Co, Al, Fe and Cr which form a layer of metal (III) hydroxide around the algal cell, adsorb copper and reduce its penetration into the cell. The degree of insolubility of the metal (III) hydroxide is related to its ability to protect against copper toxicity. In addition, manganese and cobalt catalytically scavenge damaging H2O2 and superoxide radicals, respectively, produced by the cell.

Reconstitution of Chlorophyll a/b Light-Harvesting Complexes: Xanthophyll-Dependent Assembly and Energy Transfer

Abstract: A method for in vitro reconstitution of the chlorophyll a/b light-harvesting complex from LiDodSO4/heat-denatured or acetone-extracted photosynthetic membranes has been developed. Characterization of the minimum components necessary for the functional organization of pigments in these membrane complexes reveals that xanthophylls are essential structural components.

Environmental Effects on Photosynthesis, Nitrogen-Use Efficiency, and Metabolite Pools in Leaves of Sun and Shade Plants

Abstract: Effects of varying light intensity and nitrogen nutrition on photosynthetic physiology and biochemistry were examined in the sun plant Phaseolus vulgaris (common bean) and in the shade plant Alocasia macrorrhiza (Australian rainforest floor species). In both Phaseolus and Alocasia, the differing growth regimes produced large changes in photosynthetic capacity and composition of the photosynthetic apparatus. CO2-saturated rates of photosynthesis were linearly related to leaf nitrogen (N) content in both species but photosynthesis per unit leaf N was markedly higher for Phaseolus than for Alocasia. Photosynthetic capacity was also higher in Phaseolus per unit ribulose 1,5-bisphosphate (RuBP) carboxylase (RuBPCase) protein. The leaf content of RuBPCase was linearly dependent on leaf N content in the two species. However, the proportion of leaf N which was RuBPCase was greater in Phaseolus than in Alocasia and was more sensitive to growth conditions, ranging from 6% of leaf N at low light to 20% at high light. In Alocasia, this range was much less, 6 to 11%. However, chlorophyll content was much more sensitive to light intensity in Alocasia. Thus, the RuBPCase/chlorophyll ratio was quite responsive to N availability and light intensity in both species (but for different reasons), ranging from 6 grams per gram for Phaseolus and 2 grams per gram for Alocasia at high leaf N and 1.5 gram per gram for Phaseolus and 0.5 gram per gram for Alocasia at low leaf N. These large changes in the proportions of components of the photosynthetic apparatus had marked effects on the sensitivity of these species to photoinhibition. These environmental effects also caused changes in the absolute levels of metabolites of the photosynthetic carbon reduction cycle. Concentrations of RuBP and P-glycerate were approximately 2-fold higher in high light-grown than low light-grown Phaseolus and Alocasia when expressed on a leaf area basis. However, if metabolite pool sizes are expressed on the basis of the RuBPCase catalytic site concentration, then they were little affected by the marked changes in leaf makeup. There appears to be fundamental differences between these species in the mechanism of sun-shade adaptation and N partitioning in the photosynthetic apparatus that result in significant differences in the N-use efficiency of photosynthesis between Phaseolus and Alocasia but similar RuBPCase:substrate:product ratios despite these differences.

The Nitrogen Use Efficiency of C3 and C4 Plants : III. Leaf Nitrogen Effects on the Activity of Carboxylating Enzymes in Chenopodium album (L.) and Amaranthus retroflexus (L.)

Abstract: The relationships between leaf nitrogen content per unit area (Na) and (a) the initial slope of the photosynthetic CO2 response curve, (b) activity and amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC), and (c) chlorophyll content were studied in the ecologically similar weeds Chenopodium album (C3) and Amaranthus retroflexus (C4). In both species, all parameters were linearly dependent upon leaf Na. The dependence of the initial slope of the CO2 response of photosynthesis on Na was four times greater in A. retroflexus than in C. album. At equivalent leaf Na contents, C. album had 1.5 to 2.6 times more CO2 saturated Rubisco activity than A. retroflexus. At equal assimilation capacities, C. album had four times the Rubisco activity as A. retroflexus. In A. retroflexus, a one to one ratio between Rubisco activity and photosynthesis was observed, whereas in C. album, the CO2 saturated Rubisco activity was three to four times the corresponding photosynthetic rate. The ratio of PEPC to Rubisco activity in A. retroflexus ranged from four at low Na to seven at high Na. The fraction of organic N invested in carboxylation enzymes increased with increased Na in both species. The fraction of N invested in Rubisco ranged from 10 to 27% in C. album. In A. retroflexus, the fraction of Na invested in Rubisco ranged from 5 to 9% and the fraction invested in PEPC ranged from 2 to 5%.

Origin and evolution of organisms as deduced from 5S ribosomal RNA sequences.

Abstract: A phylogenetic tree of most of the major groups of organisms has been constructed from the 352 5S ribosomal RNA sequences now available. The tree suggests that there are several major groups of eubacteria that diverged during the early stages of their evolution. Metabacteria (= archaebacteria) and eukaryotes separated after the emergence of eubacteria. Among eukaryotes, red algae emerged first; and, later, thraustochytrids (a Proctista group), ascomycetes (yeast), green plants (green algae and land plants), "yellow algae" (brown algae, diatoms, and chrysophyte algae), basidiomycetes (mushrooms and rusts), slime- and water molds, various protozoans, and animals emerged, approximately in that order. Three major types of photosynthetic eukaryotes--i.e., red algae (= Chlorophyll a group), green plants (Chl. a + b group) and yellow algae (Chl. a + c)--are remotely related to one another. Other photosynthetic unicellular protozoans--such as Cyanophora (Chl. a), Euglenophyta (Chl. a + b), Cryptophyta (Chl. a + c), and Dinophyta (Chl. a + c)--seem to have separated shortly after the emergence of the yellow algae.

Rubisco: structure, mechanisms, and prospects for improvement

Abstract: Publisher Summary D-ribulose 1,5-bisphosphate carboxylase-oxygenase's (Rubisco) central role in photosynthesis and photorespiration makes it a likely candidate for regulation, though whether it is more or less regulated than other photosynthetic enzymes remains to be seen. Rubisco's activity in vivo certainly seems to be tightly controlled, very probably by a multiplicity of mechanisms. This chapter discusses the recent advances in the understanding of Rubisco, its mechanisms of catalysis and regulation, the synthesis and assembly of its subunits, and the role of interactions between them. The only function that the glycolate pathway seems to serve is to salvage three-quarters of the carbon diverted from photosynthesis by RuBP oxygenase as phosphoglycolate. In doing so, it consumes energy in the form of ATP and reducing equivalents. Such energy consumption may be advantageous in some circumstances. For example, it may dissipate excess photosynthetic reductant under photo-inhibitory conditions associated with CO2 limitation. Rubisco stands at the interface between the inorganic and organic phases of the biosphere's carbon cycle, catalyzing the only reaction by which atmospheric CO2 may be acquired by living organisms.

Influences of Leaf Temperature on Photosynthetic Carbon Metabolism in Wheat

Abstract: Net photosynthetic assimilation rate (A), extractable activities of three photosynthetic enzymes, and the concentrations of six metabolites were determined for wheat (Tricum aestivum L.) leaves as leaf temperature was varied under photorespiring (350 microliters per liter CO(2) and 21% O(2)) and under nonphotorespiring conditions (800 microliters per liter CO(2) and 2% O(2)). The extractable activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and fructose-1,6-bisphosphatase declined with increasing leaf temperature from 15 to 45 degrees C. Leaf concentrations of ribulose-1,5-bisphosphate (RuBP) declined slightly between 15 and 25 degrees C but increased to a level which is 4 to 5 times the binding site concentration of Rubisco at leaf temperatures of 35 and 45 degrees C. Leaf concentrations of 3-phosphoglycerate, fructose-6-phosphate, and glucose-6-phosphate all declined with increasing leaf temperature. Outside of the limitations imposed by photorespiration, it is proposed that under high light and at suboptimal temperatures, A is limited by rate of utilization of triose phosphate; at optimal temperatures, by the availability of substrate (CO(2) and RuBP) under photorespiring conditions or utilization of triose phosphate under nonphotorespiring conditions; and at supraoptimal temperatures, by the activation state of Rubisco.

Effects of Nitrogen Nutrition on Electron Transport Components and Photosynthesis in Spinach

Abstract: Spinach plants (Spinacia oleracea L.) were grown in hydroponic culture in a glasshouse under full sunlight. They were supplied with different concentrations of nitrate nitrogen in solution, ranging from 1 to 12 mM, in order to produce leaves with different nitrogen contents. Oxygen evolution at CO2 saturation was measured as a function of absorbed irradiance in leaf discs with an oxygen electrode. Electron transport activities, reaction centre densities, cytochrome f and plastoquinone contents, RuP2 carboxylase and coupling factor activities and soluble protein content were measured in similar material. Although nitrogen and chlorophyll contents per unit leaf area were reduced by 60% by nitrogen deficiency, when expressed on a chlorophyll basis, thylakoid components, electron transport activities and the rate of oxygen evolution at CO2 saturation were similar between nitrogen treatments. In contrast, the content of soluble protein and RuP2 carboxylase expressed on a chlorophyll basis was greater the greater the nitrogen content per unit leaf area. Therefore the ratio of RuP2 carboxylase activity to electron transport activity increased in leaves having greater nitrogen content.

Response of vegetation to rising carbon dioxide: Photosynthesis, biomass, and seed yield of soybean

Abstract: Elevated carbon dioxide throughout the lifespan of soybean causes an increase in photosynthesis, biomass, and seed yield. A rectangular hyperbola model predicts a 32% increase in soybean seed yield with a doubling of carbon dioxide from 315 to 630 ppm and shows that yields may have increased by 13% from about 1800 A.D. to the present due to global carbon dioxide increases. Several other sets of data indicate that photosynthetic and growth response to rising carbon dioxide of many species, including woody plants, is similar to that of soybean. Calculations suggest that enough carbon could be sequestered annually from increased photosynthesis and biomass production due to the rise in atmospheric carbon dioxide from 315 ppm in 1958 to about 345 ppm in 1986 to reduce the impact of deforestation in the tropics on the putative current flux of carbon from the biosphere to the atmosphere.

The relationship between electron transport components and photosynthetic capacity in pea leaves grown at different irradiances

Abstract: Pea plants (Pisum sativum) were grown under different irradiances and the photosynthetic characteristics and chloroplast properties were determined on young, fully expanded leaves. The light-saturated rate of oxygen evolution for leaf discs, measured in 1% CO2, correlated closely with the uncoupled whole- chain electron transport activity by the thylakoid membranes. When expressed on a chlorophyll basis, the photosynthetic rate was proportional to both the cytochrome f content and the coupling factor activity. The ratio of coupling factor activity to cytochrome f content was constant across all the growth irradiance treatments. The content of photosystem II reaction centres, determined by [14C]atrazine binding, varied to a small extent while the content of photosystem I reaction centres was unaltered by growth irradiance. Reaction centres do not seem to limit the rate of non-cyclic electron transport. Analysis of the CO2 response curves suggested that the ratio of electron transport capacity to RuP2 carboxylation capacity was greater for plants grown at higher irradiances than for plants grown at lower irradiances. Within any irradiance treatment, the ratio of the two capacities was approximately constant. The proportion of leaf nitrogen allocated to thylakoid proteins (27%) was independent of growth irradiance. Adaptation to low irradiance was associated with a reduction in the electron transport components and an increase in the light-harvesting chlorophyll a/b protein such that the amount of chlorophyll per unit of thylakoid protein nitrogen increased. By contrast, adaptation to high irradiance was associated with an increase in the electron transport capacity per unit of chlorophyll such that the electron transport rate per unit of thylakoid nitrogen was increased.

Effects of drought on primary photosynthetic processes of cotton leaves.

Abstract: The effects of drought on Photosystem II (PSII) fluorescence and photosynthetic electron transport activities were analyzed in cotton. Water stress did not modify the amplitude of leaf variable fluorescence at room temperature in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) nor at 77 K. It is therefore concluded that photon collection, their distribution between the two photosystems, and PSII photochemistry are unaffected by the stress. In droughted leaves at room temperature under low exciting light, the transitory maximum (Fp) and steady state (Ft) fluorescence levels are increased; under high exciting light, Fp level and the rise time from the initial level (Fo) to Fp are unchanged, whereas Fp to Ft decay time is increased. These results infer that the drought slows the rate of plastoquinone reoxidation. This conclusion agrees with a larger proportion of reduced primary PSII electron acceptor QA measured at the steady state under low light. In thylakoids isolated from droughted leaves, PSII mediated electron flow was the same as in thylakoids from control leaves, whereas PSI mediated electron transport was inhibited. It is shown that water stress does not induce sensitization to photoinhibition in cotton.

Anapleurotic CO2 Fixation by Phosphoenolpyruvate Carboxylase in C3 Plants

Abstract: The role of phosphoenolpyruvate carboxylase in photosynthesis in the C3 plant Nicotiana tabacum has been probed by measurement of the 13C content of various materials. Whole leaf and purified ribulose bisphosphate carboxylase are within the range expected for C3 plants. Aspartic acid purified following acid hydrolysis of this ribulose bisphosphate carboxylase is enriched in 13C compared to whole protein. Carbons 1-3 of this aspartic acid are in the normal C3 range, but carbon-4 (obtained by treatment of the aspartic acid with aspartate β-decarboxylase) has an isotopic composition in the range expected for products of C4 photosynthesis (−5‰), and it appears that more than half of the aspartic acid is synthesized by phosphoenolpyruvate carboxylase using atmospheric CO2/HCO3−. Thus, a primary role of phosphoenolpyruvate carboxylase in C3 plants appears to be the anapleurotic synthesis of four-carbon acids.

Interactions between internal and external co2 pools in the photosynthesis of the aquatic cam plants littorella uniflora (l.) aschers and isoetes lacustris l.

Abstract: Summary The significance of CAM as a carbon-conserving mechanism in two submerged aquatics, Littorella uniflora (L.) Aschers and hoetes lacustris L., was evaluated by determining (1) the loss of previously fixed CO2, released through decarboxylation of malic acid and (2) the quantitative importance of CAM relative to external CO2 uptake in photosynthesis. Using a 14C-labelling technique it was found that the loss of CO2 derived from decarboxylation of malic acid constituted less than 2 % of nocturnal carbon uptake, confirming that the diurnal rhythm of acidity provides a good measure of the incorporation of carbon via CAM. The exchange pattern of inorganic carbon and oxygen was measured for plants incubated in open flow-through systems. The contribution of internal and external CO2 to photosynthesis was determined as the difference in CO, uptake and oxygen release, where excess oxygen release reflected the assimilation of CO2 released from deacidification of malic acid. Despite a rapid deacidification, uptake of external CO2 was stimulated by 15 to 30% at intermediate external CO2 concentrations. It is suggested that this effect was due to a reduced photorespiratory activity caused by an enhanced internal CO2 concentration generated from malic acid. The simultaneous uptake of inorganic carbon from high internal and low external CO2 concentrations can only be explained by assuming a non-linear CO, gradient from the lacunal air to the bulk medium, with the CO2 concentration in the outermost cell layers being lower than both the bulk medium and the lacunal air. The relative contribution of CAM to the total uptake of CO2 in daytime declined from 95% (both species) at an external CO2 concentration of 30μ CO2 to 38% (Littorella) and 34% (Isoetes) at 200μ CO2. This resulted from increased uptake of external CO2 at high external CO2 concentrations and a parallel suppression of internal decarboxylation of malic acid. The observed suppression of decarboxylation was confirmed by following the time course in the content of titratable acidity of the leaves. A reversible inhibition of daytime deacidification was seen for external CO2 concentrations higher than 3.0 to 5.4 mM CO2 in both Littorella and Isoetes. The functional significance of CAM for aquatics rests in the enhanced capacity for obtaining inorganic carbon resulting from the extension of the diel period in which inorganic carbon can be accumulated and in the high reassimilation efficiency of nocturnal respiratory CO2.

Control of Photosynthetic Sucrose Formation

Abstract: Publisher Summary This chapter discusses the control of photosynthetic sucrose formation. In most species, starch and sucrose are the principal end products of photosynthesis. It is clear that the formation of both carbohydrates is highly regulated biochemically. The interdependence of chloroplast and cytosolic metabolism implies that coordination of the fluxes and conditions in these compartments is a precondition for rapid photosynthesis. This interaction is defined by the stoichiometry of carbon and phosphate flow during steady-state photosynthesis. Chloroplasts convert three CO2 and one Pi to one molecule of triose-P, and a continuation of photosynthesis depends on the triose-P being removed and more Pi becoming available. This is achieved by exporting triose-P from the chloroplast, in exchange for Pi. However, the rate of this exchange must be coordinated with the rate of CO2 fixation, because only one-sixth of the triose-P may be removed, representing the net gain of carbon in one turn of the Calvin cycle.