Ascobic acid and photosynthesis: II. Anaerobic photo-oxidation of ascorbic acid by chloroplast fragments and by whole chloroplasts

Abstract

The relatively low ability of whole chloroplasts of photo-oxidize AA in the absence of intermediate electron carriers (such as DPIP or quinones) is greatly increased when the chloroplasts are disrupted either by hypotonic treatment or with digitonin. High values of AA photo-oxidation are observed even in the absence of oxygen, provide that an [H] trapping system ( e.g. TPN, glutathione reductase and oxidized glutathione) is present. However, even whole chloroplasts supplemented with the glutathione trapping system photo-oxidize AA (under aerobic or anaerobic conditions) at rates similar to or higher than those observed for chloroplast fragments. These results are interpreted as indicating that the ultimate electron acceptor in AA photo-oxidation is the oxidizing agent produced in photolysis of water, and that in the illuminated whole chloroplasts, an AA/MDHA system is continuously subjected to two opposite processes, one of oxidation and the other of reduction, both strictly depending on the photolysis of water.