REVIEW: Oxygen Reduction in Chloroplasts and the Ascorbate Cycle

B. N. Ivanov

Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (0967) 79-0532; E-mail: ivabor@issp.serpukhov.su

Received August 22, 1997; Revision received September 10, 1997

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Current views concerning the generation of superoxide radicals and hydrogen peroxide in chloroplasts as well as their toxic influences on photosynthesis are presented. Systems of H₂O₂ detoxification including the ascorbate peroxidase reactions and the ascorbate regenerating reactions are described. Data concerning mechanisms of monodehydroascorbate reduction by the photosynthetic electron transport chain are reviewed. The participation of the Mehler-peroxidase reaction in building of a proton gradient across the thylakoid membrane and its possible input in ATP synthesis and in protection from photoinhibition are analyzed. Ascorbate functions in chloroplasts and the need to consider the high concentration of ascorbate in chloroplasts when photosynthetic reactions in vivo are discussed are briefly reviewed.

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KEY WORDS: chloroplasts, superoxide radical, hydrogen peroxide, Mehler-peroxidase reaction, ascorbate

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