PHOTOSYNTHETIC GENERATION OF O-2 AND H-2 BY PHOTOSYSTEM I-DEFICIENT CHLAMYDOMONAS MUTANTS

A comparative study of aerobic generation of O-2 and anaerobic photopr oduction of H-2 in whole cells of a wild-type strain of Chlamydomonas reinhardtii and its photosystem I-deficient mutants B4 and F8 found no contribution of photosystem II to ferredoxin photoreduction, which is not consistent with data of recent studies by Greenbaum et al. (Natur e, 1995, 376, 438-441; and Science, 1996, 273, 364-367) who reported t hat they had discovered such a capacity in these mutant strains. In th e wild-type and mutant strains, action spectra showed that O, was evol ved by photosystem II, whereas photoinhibition of chlororespiration an d evolution of H-2 depended on the activity of photosystem I. Single-t urnover flash measurements of H-2 evolution showed that the contents o f photosystem I in mutant strains amounted to 3-35% of that in the wil d-type strain. This fraction of photosystem I in ''leaky'' mutants dis played abnormal kinetic features and was highly sensitive to photoinhi bition.