Mutant strains of Chlamydomonas reinhardi with lesions on the oxidizing side of photosystem II

Abstract

1. Two mutant strains of the unicellular green alga, Chlamydomonas reinhardi, having lesions on the oxidizing side of photosystem II, have been obtained using a selection and screening technique that facilitates the isolation of photosynthetic mutant strains having lesions either on the oxidizing or reducing side of photosystem II. 2. Chloroplast fragments obtained from the two strains lack Hill activity. However, they exhibit normal rates of NADP + photoreduction with an artificial electron donor to photosystem I. Fluorescence yield changes are absent in the chloroplast fragments obtained from both strains. 3. In the presence of electron donor systems to photosystem II, the mutant strains exhibit fluorescence yield changes and a 3(3,4-dichlorophenyl)-1,1-dimethyl-urea-sensitive photoreduction of NADP + that are characteristic of the wild-type strain. 4. Based on what is generally regarded to be the nature of photosystem II, mutant strains having lesions on the oxidizing side of photosystem II should exhibit an invariant high fluorescence yield. The abnormally low fluorescence yield exhibited by the mutant strains can be explained if it is assumed that there is a back reaction between a component on the reducing side of photosystem II and one on the oxidizing side.