Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Photosynthesis by Flag Leaves of Wheat in Relation to Protein, Ribulose Bisphosphate Carboxylase Activity and Nitrogen Supply

Abstract: The effects of nitrate supply on the composition (cell numbers, protein and chlorophyll contents) of flag leaves of winter wheat grown with two amounts of N fertilizer and of spring wheat grown in the glasshouse under controlled nitrate supply are described and related to photosynthesis. Nitrogen deficiency decreased the size of leaves, mainly by reducing cell number and, to a smaller extent, by decreasing cell volume. Protein content per unit leaf area, per cell and per unit cell volume was larger with abundant N. Total soluble protein, ribulose tophosphate carboxylase-oxygenase (RuBPc-o) protein and chlorophyll changed in proportion irrespective of nitrogen supply and leaf age. Photosynthesis per unit area of flag leaf and carboxylation efficiency in both winter and spring wheat were proportional to the amount of total soluble protein up to 7-0 g m~ and to the amount of RuBPc-o protein up to 40 g m~. However, photosynthesis did not increase in proportion to the amount of total soluble or RuBPc-o protein above these amounts. In young leaves with a high protein content the measured rates of photosynthesis were lower than expected from the amount and activity of RuBPc-o. Carboxylation per unit of RuBPc-o protein, measured in vitro, was slightly greater in N-deficient leaves of winter wheat but not of spring wheat. RuBPc-o activity per unit of RuBPc-o protein was similar in winter and spring wheat leaves and remained approximately constant with age, but increased in leaves showing advanced senescence. RuBPc-o protein from N-deficient leaves migrated faster on polyacrylamide gels than protein from leaves with high N content. Regulation of the rate of photosynthesis in leaves and chloroplasts with a high protein content is discussed. The conductance of the cell to the flux of CO2 from intercellular spaces to RuBPc-o active sites is calculated, from cell surface areas and CO2 fluxes, to decrease the CO2 partial pressure at the active site by less than 0-8 Pa at an internal CO2 partial pressure of 34 Pa. Thus the decrease in partial pressure of CO2 is insufficient to account for the inefficiency of RuBPc-o in vivo at high protein contents. Other limitations to the rate of photosynthesis are considered.

Chloroplast Response to Low Leaf Water Potentials III. Differing Inhibition of Electron Transport and Photophosphorylation

Abstract: Cyclic and noncyclic photophosphorylation and electron transport by photosystem 1, photosystem 2, and from water to methyl viologen ("whole chain") were studied in chloroplasts isolated from sunflower (Helianthus annus L. var Russian Mammoth) leaves that had been desiccated to varying degrees. Electron transport showed considerable inhibition at leaf water potentials of -9 bars when the chloroplasts were exposed to an uncoupler in vitro, and it continued to decline in activity as leaf water potentials decreased. Electron transport by photosystem 2 and coupled electron transport by photosystem 1 and the whole chain were unaffected at leaf water potentials of -10 to -11 bars but became progressively inhibited between leaf water potentials of -11 and -17 bars. A low, stable activity remained at leaf water potentials below -17 bars. In contrast, both types of photophosphorylation were unaffected by leaf water potentials of -10 to -11 bars, but then ultimately became zero at leaf water potentials of -17 bars. Although the chloroplasts isolated from the desiccated leaves were coupled at leaf water potentials of -11 to -12 bars, they became progressively uncoupled as leaf water potentials decreased to -17 bars. Abscisic acid and ribonuclease had no effect on chloroplast photophosphorylation. The results are generally consistent with the idea that chloroplast activity begins to decrease at the same leaf water potentials that cause stomatal closure in sunflower leaves and that chloroplast electron transport begins to limit photosynthesis at leaf water potentials below about -11 bars. However, it suggests that, during severe desiccation, the limitation may shift from electron transport to photophosphorylation.

Acclimation of photosynthetic capacity in Scots pine to the annual cycle of temperature.

Abstract: Coniferous trees growing in the boreal and temperate zones have a clear annual cycle of photosynthetic activity. A recent study demonstrated that the seasonal variation in photosynthetic capacity of Scots pine (Pinus sylvestris L.) could be attributed mainly to the light response curve of photosynthesis. The magnitude of the light response curve varied over the season while its shape remained constant, indicating that the two physiological parameters quantifying the curve-the quantum yield per unit internal carbon dioxide concentration and the corresponding light-saturated rate-remained proportional to each other. We now show, through modeling studies, that the quantum yield (and hence the light-saturated rate) is related to the annual cycle of temperature through a delayed dynamic response. The proposed model was tested by comparing model results with intensive measurements of photosynthesis and driving variables made from April to October in three shoots of Scots pine growing near the northern timberline. Photosynthetic capacity showed considerable acclimation during the growing season. A single model describing photosynthetic capacity as a reversible, first-order delay process driven by temperature explained most of the variation in photosynthetic capacity during the year. The proposed model is simpler but no less accurate than previous models of the annual cycle of photosynthetic capacity.

Self-sustained phototrophic microbial fuel cells based on the synergistic cooperation between photosynthetic microorganisms and heterotrophic bacteria.

Abstract: A sediment-type self-sustained phototrophic microbial fuel cell (MFC) was developed to generate electricity through the synergistic interaction between photosynthetic microorganisms and heterotrophic bacteria. Under illumination, the MFC continuously produced electricity without the external input of exogenous organics or nutrients. The current increased in the dark and decreased with the light on, possibly because of the negative effect of the oxygen produced via photosynthesis. Continuous illumination inhibited the current production while the continuous dark period stimulated the current production. Extended darkness resulted in a decrease of current, probably because of the consumption of the organics accumulated during the light phase. Using color filters or increasing the thickness of the sediment resulted in a reduction of the oxygen-induced inhibition. Molecular taxonomic analysis revealed that photosynthetic microorganisms including cyanobacteria and microalgae predominated in the water phase, adjacent to the cathode and on the surface of the sediment. In contrast, the sediments were dominated by heterotrophic bacteria, becoming less diverse with increasing depth. In addition, results from the air-cathode phototrophic MFC confirmed the light-induced current production while the test with the two-chamber MFC (in the dark) indicated the presence of electricigenic bacteria in the sediment.