Photosynthesis

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

Energy Conservation in Photosynthetic Electron Transport of Chloroplasts

Abstract: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 ELECTRON ACCEPTOR OF PHOTOSYSTEM I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 Endogenous Electron Acceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 Localization of the Acceptor Site of Photosystem I in the Membrane. . . . . . . . . . . . 428 ELECTRON DONOR OF PHOTOSYSTEM I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Endogenous Electron Donor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431 Artificial Electron Donors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 Cyclic Electron Flow Around Photosystem I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 Localization of the Donor Site of Photosystem I in the Membrane . . . . . . . . . . . . . . 433 ELECTRON ACCEPTOR OF PHOTOSYSTEM II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 Endogenous Electron Acceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 Artificial Electron Acceptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436 Localization of the Acceptor Site of Photosystem II in the Membrane . . . . . . . . . . . 437 ELECTRON DONOR OF PHOTOSYSTEM II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Endogenous Electron Donor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 Artificial Electron Donors ............................. : . . . . . . . . . . . . . . . . . . 439 Localization of the Donor Site of Photosystem II in the Membrane . . . . . . . . . . . . . 440 FURTHER EVIDENCE FOR THE SIDED NESS OF THE MEMBRANE ................ 441 NONCYCLIC AND CYCLIC ELECTRON FLOW ACROSS THE THYLAKOID MEMBRANE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 ENERGY CONSERVATION IN PHOTOSYNTHETIC ELECTRON FLOW.............. 451

Response of the photosynthetic apparatus of Phaeodactylum tricornutum (Bacillariophyceae) to nitrate, phosphate, or iron starvation

Abstract: The effects of nitrate, phosphate, and iron starvation and resupply on photosynthetic pigments, selected photosynthetic proteins, and photosystem II (PSII) photochemistry were examined in the diatom Phaeodactylum tricornutum Bohlin (CCMP 1327). Although cell chlorophyll a (chl a) content decreased in nutrient-starved cells, the ratios of light-harvesting accessory pigments (chl c and fucoxanthin) to chl a were unaffected by nutrient starvation. The chl a-specific light absorpition coefficient (a*) and the functional absorption cross-section of PSII (σ) increased during nutrient starvation, consistent with reduction of intracellular self-shading (i.e. a reduction of the “package effect”) as cells became chlorotic. The light-harvesting complex proteins remained a constant proportion of total cell protein during nutrient starvation, indicating that chlorosis mirrored a general reduction in cell protein content. The ratio of the xanthophylls cycle pigments diatoxanthin and diadinoxanthin to chl a increased during nutrient starvation. These pigments are thought to play a photo-protective role by increasing dissipation of excitation energy in the pigment bed upstream from the reaction centers. Despite the increase in diatoxanthin and diadinoxanthin, the efficiency of PSII photochemistry, as measured by the ration of variable to maximum fluorescence (Fv/Fm) of dark-adapted cells, declined markedly under nitrate and iron starvation and moderately under phosphate starvation. Parallel to changes in Fv/Fm were decreases in abundance of the reaction center protein D1 consistent with damage of PSII reaction centers in nutrient-starved cells. The relative abundance of the carboxylating enzyme, ribulose bisphosphate carboxylase/oxygenase (RUBISCO), decreased in response to nitrate and iron starvation but not phosphate starvation. Most marked was the decline in the abundance of the small subunit of RUBISCO in nitrate-starved cells. The changes in pigment content and fluorescence characteristics were typically reversed within 24 h of resupply of the limiting nutrient.

Photosynthesis or persistence: nitrogen allocation in leaves of evergreen and deciduous Quercus species

Abstract: Photosynthetic nitrogen use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) is one of the most important factors for the interspecific variation in photosynthetic capacity. PNUE was analysed in two evergreen and two deciduous species of the genus Quercus. PNUE was lower in evergreen than in deciduous species, which was primarily ascribed to a smaller fraction of nitrogen allocated to the photosynthetic apparatus in evergreen species. Leaf nitrogen was further analysed into proteins in the water-soluble, the detergent-soluble, and the detergent-insoluble fractions. It was assumed that the detergent-insoluble protein represented the cell wall proteins. The fraction of nitrogen allocated to the detergent-insoluble protein was greater in evergreen than in deciduous leaves. Thus the smaller allocation of nitrogen to the photosynthetic apparatus in evergreen species was associated with the greater allocation to cell walls. Across species, the fraction of nitrogen in detergent-insoluble proteins was positively correlated with leaf mass per area, whereas that in the photosynthetic proteins was negatively correlated. There may be a trade-off in nitrogen partitioning between components pertaining to productivity (photosynthetic proteins) and those pertaining to persistence (structural proteins). This trade-off may result in the convergence of leaf traits, where species with a longer leaf life-span have a greater leaf mass per area, lower photosynthetic capacity, and lower PNUE regardless of life form, phyllogeny, and biome.