OXYGEN REDUCTION IN CHLOROPLASTS AND THE ASCORBATE CYCLE

Current views concerning the generation of superoxide radicals and hyd rogen peroxide in chloroplasts as well as their toxic influences on ph otosynthesis are presented. Systems of H2O2 detoxification including t he ascorbate peroxidase reactions and the ascorbate regenerating react ions 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 reactio ns in vivo are discussed are briefly reviewed.