Photooxidation of 3,3′-diaminobenzidine by blue-green algae and Chlamydomonas reinhardii

Abstract

1. 1. The photooxidation of 3,3′-diaminobenzidine was investigated in whole cells of the wild-type and two mutant strains of Chlamydomonas reinhardii and in four species of blue-green algae. 2. 2. In the wild-type strain, this reaction is insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea and is dependent on the presence of methyl viologen. The photooxidation can be demonstrated in a mutant strain lacking Photosystem II activity. However, it is absent from a mutant strain deficient in Photosystem I activity. 3. 3. Experiments performed with chloroplast fragments isolated from the wildtype and mutant strains yielded results similar to those obtained with whole cells. These results established that the photooxidation of 3,3′-diaminobenzidine is mediated by Photosystem I only. 4. 4. In contrast to Chlamydomonas reinhardii, blue-green algae are able to photooxidize 3-3′-diaminobenzidine at high rates in the absence of methyl viologen. This property is attributed to the ability of the primary electron acceptor of Photosystem I to undergo autooxidation in vivo. 5. 5. The possible applications of this reaction in the studies of photosynthetic electron transport reactions in intact algae and in the investigations of chloroplast substructures are discussed.