Light-dependent development of photosynthetic competence in Scenedesmus mutant No. 8

The heterotrophically grown, P-700-free mutant No. 8 of Scenedesmus obliquus is unable to carry out photosynthesis. Yet, chloroplast particles isolated from the alga reduced ferricyanide. They also reduced methyl viologen in the presence of the artificial donor reduced 2,6-dichlorophenol indophenol with a low yield but an appreciable saturation rate. NADP reduction or P-700 turn-over could not be detected. When grown mixotrophically, the mutant showed increasing P-700 activity with a concomitant increase in the rate of photosynthesis. Both activities were lost again when the algae were returned to darkness. Isolated chloroplast particles showed a good P-700 turn-over and reasonable rates of NADP reduction. The data suggest that the mutation occurred at a site preceding the formation of the pigment. The results on the photochemical activities are discussed in the light of reports concerning the involvement of P-700 in linear electron transport.