Nutritional Regulation of Organelle Biogenesis in Euglena

Abstract

Nitrogen deficiency and the presence of specific organic carbon sources prevent chloroplast development in Euglena. In exponentially growing cultures, chlorophyll levels were low and independent of the nitrogen content of the growth medium. Chlorophyll levels increased in stationary phase and the amount of chlorophyll formed was proportional to the initial nitrogen content of the growth medium; the greater the concentration of nitrogen, the greater the amount of chlorophyll synthesized during stationary phase. Washing experiments demonstrated that the major nutritional factor inhibiting chlorophyll synthesis in stationary phase cultures grown on medium containing a high carbon to nitrogen ratio was the absence of nitrogen rather than the presence of utilizable organic carbon.The light-induced synthesis of chlorophyll and of NADP-glyceraldehyde-3-phosphate dehydrogenase was inhibited when acetate or ethanol was added at the time of exposure of dark-grown resting cells to light. Malate addition, however, stimulated chlorophyll and enzyme synthesis. Both cell number and total cell protein increased after ethanol, acetate, or malate addition, indicating that the resting cells were not nitrogen-deficient. Ethanol and acetate specifically repress light-induced chlorophyll synthesis. NADP-glyceraldehyde-3-phosphate dehydrogenase synthesis was inhibited at a time, the first 24 hours of light exposure, when chlorophyll synthesis was unaffected by carbon addition.