THE ROLE OF RESPIRATION AND PHOTOSYNTHESIS IN THE CHLOROPLAST REGENERATION IN THE “GLUCOSE-BLEACHED” CELLS OF CHLORELLA PROTOTHECOIDES

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1. As previously demonstrated, entirely chlorophyll-less cells of Chlorella protothecoides are obtained when the alga is grown in a medium rich in glucose and poor in nitrogen source (urea). These cells, which are referred to as “glucose-bleached” cells, have neither discernible chloroplast structures nor photosynthetic activity. When the “glucose-bleached” cells are incubated, in the light, in a nitrogen-enriched mineral medium without added glucose, they turn green, after an induction period, with regeneration of chloroplasts and development of the capacity for performing normal photosynthesis. In the present study, changes in respiratory activity of algal cells during the process of greening (chloroplast regeneration) were followed, and the effects of various inhibitors of respiration and photosynthesis on the greening process were examined. 2. The glucose-bleached cells showed a very low activity of respiration, and the activity increased markedly during an early phase of chloroplast regeneration, showing, however, a decrease during the subsequent phase of greening. 3. Some antimetabolites which inhibited the cell respiration, were found to suppress also the greening of cells. 2,4-Dinitrophenol and azide, potent inhibitors of oxidative phosphorylation, accelerated considerably both the respiration and greening of algal cells. CMU inhibited completely photosynthesis of the greening cells, but suppressed only slightly the greening process. 4. Based on these results it was concluded that the primary role of respiration in the chloroplast regeneration in the glucose-bleached cells is to produce oxidized carbon compounds (and perhaps reduced forms of NAD and NADP) for various biosynthetic reactions. It was further suggested that ATP may be supplied for the chloroplast regeneration by a certain means different from the oxidative phosphorylation or photophosphorylation. The activities of photosynthetic phosphorylation and CO2-fixation developing in the greening cells do not appear to play any essential role in the chloroplast regeneration.