Photosynthesis

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

Distinctive Responses of Ribulose-1,5-Bisphosphate Carboxylase and Carbonic Anhydrase in Wheat Leaves to Nitrogen Nutrition and their Possible Relationships to CO2-Transfer Resistance

Abstract: The amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), total chlorophyll (Chl), and total leaf nitrogen were measured in fully expanded, young leaves of wheat (Triticum aestivum L.), rice (Oryza sativa L.), spinach (Spinacia oleracea L.), bean (Phaseolus vulgaris L.), and pea (Pisum sativum L.). In addition, the activities of whole-chain electron transport and carbonic anhydrase were measured. All plants were grown hydroponically at different nitrogen concentrations. Although a greater than proportional increase in Rubisco content relative to leaf nitrogen content and Chl was found with increasing nitrogen supply for rice, spinach, bean, and pea, the ratio of Rubisco to total leaf nitrogen or Chl in wheat was essentially independent of nitrogen treatment. In addition, the ratio of Rubisco to electron transport activities remained constant only in wheat. Nevertheless, gas-exchange analysis showed that the in vivo balance between the capacities of Rubisco and electron transport in wheat, rice, and spinach remained almost constant, irrespective of nitrogen treatment. The in vitro carbonic anhydrase activity in wheat was very low and strongly responsive to increasing nitrogen content. Such a response was not found for the other C3 plants examined, which had 10- to 30-fold higher carbonic anhydrase activity than wheat at any leaf-nitrogen content. These distinctive responses of carbonic anhydrase activity in wheat were discussed in relation to CO2-transfer resistance and the in vivo balance between the capacities of Rubisco and electron transport.

Arsenic(III) fuels anoxygenic photosynthesis in hot spring biofilms from Mono Lake, California.

Abstract: Phylogenetic analysis indicates that microbial arsenic metabolism is ancient and probably extends back to the primordial Earth. In microbial biofilms growing on the rock surfaces of anoxic brine pools fed by hot springs containing arsenite and sulfide at high concentrations, we discovered light-dependent oxidation of arsenite [As(III)] to arsenate [As(V)] occurring under anoxic conditions. The communities were composed primarily of Ectothiorhodospira-like purple bacteria or Oscillatoria-like cyanobacteria. A pure culture of a photosynthetic bacterium grew as a photoautotroph when As(III) was used as the sole photosynthetic electron donor. The strain contained genes encoding a putative As(V) reductase but no detectable homologs of the As(III) oxidase genes of aerobic chemolithotrophs, suggesting a reverse functionality for the reductase. Production of As(V) by anoxygenic photosynthesis probably opened niches for primordial Earth's first As(V)-respiring prokaryotes.

On the Function of Mitochondrial Metabolism during Photosynthesis in Spinach (Spinacia oleracea L.) Leaves (Partitioning between Respiration and Export of Redox Equivalents and Precursors for Nitrate Assimilation Products).

Abstract: The functioning of isolated spinach (Spinacia oleracea L.) leaf mitochondria has been studied in the presence of metabolite concentrations similar to those that occur in the cytosol in vivo. From measurements of the concentration dependence of the oxidation of the main substrates, glycine and malate, we have concluded that the state 3 oxidation rate of these substrates in vivo is less than half of the maximal rates due to substrate limitation. Analogously, we conclude that under steady-state conditions of photosynthesis, the oxidation of cytosolic NADH by the mitochondria does not contribute to mitochondrial respiration. Measurements of mitochondrial respiration with glycine and malate as substrates and in the presence of a defined malate:oxaloacetate ratio indicated that about 25% of the NADH formed in vivo during the oxidation of these metabolites inside the mitochondria is oxidized by a malate-oxaloacetate shuttle to serve extramitochondrial processes, e.g. reduction of nitrate in the cytosol or of hydroxypyruvate in the peroxisomes. The analysis of the products of the oxidation of malate indicates that in the steady state of photosynthesis the activity of the tricarboxylic acid cycle is very low. Therefore, we have concluded that the mitochondrial oxidation of malate in illuminated leaves produces mainly citrate, which is converted via cytosolic aconitase and NADP-isocitrate dehydrogenase to yield 2-oxoglutarate as the precursor for the formation of glutamate and glutamine, which are the main products of photosynthetic nitrate assimilation.