Formation of Hydrogen Peroxide and Oxygen Dependence of Photosynthetic CO_2 Assimilation by Intact Chloroplasts

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概要

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• 1. Hydrogen peroxide excretion by photosynthesizing intact spinach chloroplasts was determined. The rates were dependent on the oxygen concentration and on the ATP/NADPH requirement of the final electron acceptor. Upon CO_2 assimilation a maximum rate of 0.9μmol H_2O_2/mg chlorophyll/hr and half saturation at 7.5×10^<-5>_M O_2 were found. Excretion of H_2O_2 was considerably reduced upon photosynthetic reduction of glycerate 3-phosphate or oxaloacetate. 2. Light- and HCO_3^--saturated CO_2 assimilation was inhibited by more than 50% by anaerobic conditions, whereupon quantum efficiency was also drastically decreased. However, no anoxic influence was detected with glycerate 3-phosphate as the terminal electron acceptor and the quantum requirement with this acceptor was not increased by anaerobiosis. Thus the enhancing effect of oxygen on CO_2 assimilation was ascribed to an improvement of photosynthetic ATP supply. 3. Since the stimulation of anaerobic photosynthetic CO_2 assimilation by oxygen was markedly greater than the concomitant increase in H_2O_2 evolution, photosynthetic oxygen reduction alone is not sufficient to produce the required additional ATP for the observed enhanced CO_2 assimilation. But it provides a means to avoid the over-reduction of photosynthetic electron carriers and thus enables aerobic cyclic photophosphorylation. This supports the hypothesis that cyclic photophosphorylation is not an alternative to ATP formation by "pseudocyclic" electron transport, but rather that it depends on the latter.

• 日本植物生理学会の論文

著者

• Steiger Hans-martin

  Lehrstuhl Fur Pfianzenphvsio!ogie Universitat Bayreulh

• Beck Erwin

  Lehrstuhl Fur Pfianzenphvsio!ogie Universitat Bayreulh

関連論文

• Nitrate Reductase Activity of Photoautotrophic Suspension Culture Cells of Chenopodium rubrum is under the Hierarchical Regime of NO_3^-, NH_4^+ and Light
• Ammonium Triggers Uptake of NO_3^- by Chenopodium rubrum Suspension Culture Cells and Remobilization of their Vacuolar Nitrate Pool
• Formation of Hydrogen Peroxide and Oxygen Dependence of Photosynthetic CO_2 Assimilation by Intact Chloroplasts

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