Regulation of Photosynthesis in Chlamydomonas reinhardi

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Abstract
The activities of several photosynthetic reactions were studied in the wild type and in 4 mutant strains of C. reinhardi. The activity of ribulose, 1,5-diphosphate (RuDP) carboxylase was relatively independent of growth conditions in the wild type and in 4 acetate-requiring mutants. Large changes in the activity of this enzyme were seen only in extracts of the mutant strain y-2 during heterotrophic growth in the dark, under which no chlorophyll is synthesized. Changes in the rates of CO2 fixation, O2 evolution and TPN photoreduction closely paralleled changes in chlorophyll content during both bleaching and regreening. Changes in the activities of RuDP carboxylase and photosynthetic pyridine nucleotide reductase resembled each other, but were shown to be only indirectly related to changes in chlorophyll content. Of several possible explanations for this indirect relationship, it was considered most probable that the development of an active chloroplast structure is the factor which triggers rapid increase in the activities of these enzymes during regreening.