Photosynthesis

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

Dunaliella salina (Chlorophyta) with small chlorophyll antenna sizes exhibit higher photosynthetic productivities and photon use efficiencies than normally pigmented cells

Abstract: The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light (LL: 100 μmol photon m-2 s-1) or high-light (HL: 2000 μmol photon m-2 s-1) conditions. Under LL, cells were normally pigmented (deep green) containing ∼500 chlorophyll (Chl) molecules per photosystem II (PSII) unit and ∼250 Chl molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chl per PSII and 100 Chl per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at ∼200 μmol photon m-2 s-1 with a rate (Pmax) of ∼100 mmol O2 (mol Chl)-1 s-1. In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. ∼2500 μmol photon m-2 s-1, and exhibited a three-fold higher Pmax (∼300 mmol O2 (mol Chl)-1 s-1) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting Chl antenna size increase, enhanced Pmax to ∼675 mmol O2 (mol Chl)-1 s-1. Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chl antenna size could exhibit 2–3 times higher productivities than currently achieved with normally pigmented cells.

Lipids in photosynthesis: structure, function and genetics.

Abstract: Preface. 1. Lipids in Photosynthesis: An Overview N. Murata, P.-A. Siegenthaler. 2. Structure, Distribution and Biosynthesis of Glycerolipids from Higher Plant Chloroplasts J. Joyard, et al. 3. Membrane Lipids in Algae J.L. Harwood. 4. Membrane Lipids in Cyanobacteria H. Wada, N. Murata. 5. Membrane Lipids in Anoxygenic Photosynthetic Bacteria C. Benning. 6. The Physical Properties of Thylakoid Membrane Lipids and Their Relation to Photosynthesis W.P. Williams. 7. Molecular Organization of Acyl Lipids in Photosynthetic Membranes of Higher Plants P.-A. Siegenthaler. 8. Role of Acyl Lipids in the Function of Photosynthetic Membranes in Higher Plants P.-A. Siegenthaler, A. Tremolieres. 9. Reconstitution of Photosynthetic Structures and Activities with Lipids A. Tremolieres, P.-A. Siegenthaler. 10. Lipid-Protein Interactions in Chloroplast Protein Import B. de Kruijff, et al. 11. Development of Thylakoid Membranes with Respect to Lipids E. Selstam. 12. Triglycerides as Products of Photosynthesis. Genetic Engineering, Fatty Acid Composition and Structure of Triglycerides D. Facciotti, V. Knauf. 13. Genetic Engineering of the Unsaturation of Membrane Glycerolipid: Effects on the Ability of the Photosynthetic Machinery to Tolerate Temperature Stress Z. Gombos, N. Murata. 14. A Genetic Approach to Investigating Membrane Lipid Structure and Photosynthetic Function P. Vijayan, et al. 15. Involvement of Chloroplast Lipids in the Reaction of Plants Submitted to Stress J.L. Harwood. Index.

BIOGENESIS OF CHLOROPLAST MEMBRANES : I. Plastid Dedifferentiation in a Dark-Grown Algal Mutant (Chlamydomonas reinhardi)

Abstract: This paper describes the morphology and photosynthetic activity of a mutant of Chlamydomonas reinhardi (y-1) which is unable to synthesize chlorophyll in the dark. When grown heterotrophically in the light, the mutant is indistinguishable from the wild type Chlamydomonas. When grown in the dark, chlorophyll is diluted through cell division and the photosynthetic activity (oxygen evolution, Hill reaction, and photoreduction of NADP) decays at a rate equal to or faster than that of chlorophyll dilution. However, soluble enzymes associated with the photosynthetic process (alkaline FDPase, NADP-linked G-3-P dehydrogenase, RuDP carboxylase), as well as cytochrome f and ferredoxin, continue to be present in relatively high concentrations. The enzymes involved in the synthesis of the characteristic lipids of the chloroplast (including mono- and digalactoside glycerides, phosphatidyl glycerol, and sulfolipid) are still detectable in dark-grown cells. Such cells accumulate large amounts of starch granules in their plastids. On onset of illumination, dark-grown cells synthesize chlorophyll rapidly, utilizing their starch reserve in the process. At the morphological level, it was observed that during growth in the dark the chloroplast lamellar system is gradually disorganized and drastically decreased in extent, while other subchloroplast components are either unaffected (pyrenoid and its tubular system, matrix) or much less affected (eyespot, ribosomes). It is concluded that the dark-grown mutant possesses a partially differentiated plastid and the enzymic apparatus necessary for the synthesis of the chloroplast membranes (discs). The advantage provided by such a system for the study of the biogenesis of the chloroplast photosynthetic membranes is discussed.

Photosynthesis and ion content of leaves and isolated chloroplasts of salt-stressed spinach.

Abstract: Spinach (Spinacia oleracea) plants were subjected to salt stress by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar. Plants were harvested 3 weeks after starting NaCl treatment. Fresh and dry weight of both shoots and roots was decreased more than 50% compared to control plants but the salt-stressed plants appeared healthy and were still actively growing. The salt-stressed plants had much thicker leaves. The salt-treated plants osmotically adjusted to maintain leaf turgor. Leaf K(+) was decreased but Na(+) and Cl(-) were greatly increased.The potential photosynthetic capacity of the leaves was measured at saturating CO(2) to overcome any stomatal limitation. Photosynthesis of salt-stressed plants varied only by about 10% from the controls when expressed on a leaf area or chlorophyll basis. The yield of variable chlorophyll a fluorescence from leaves was not affected by salt stress. Stomatal conductance decreased 70% in response to salt treatment.Uncoupled rates of electron transport by isolated intact chloroplasts and by thylakoids were only 10 to 20% below those for control plants. CO(2)-dependent O(2) evolution was decreased by 20% in chloroplasts isolated from salt-stressed plants. The concentration of K(+) in the chloroplast decreased by 50% in the salt-stressed plants, Na(+) increased by 70%, and Cl(-) increased by less than 20% despite large increases in leaf Na(+) and Cl(-).It is concluded that, for spinach, salt stress does not result in any major decrease in the photosynthetic potential of the leaf. Actual photosynthesis by the plant may be reduced by other factors such as decreased stomatal conductance and decreased leaf area. Effective compartmentation of ions within the cell may prevent the accumulation of inhibitory levels of Na(+) and Cl(-) in the chloroplast.