Environmental control of carbohydrate and lipid synthesis in euglena

Dark-grown and light-grown nitrogen deficient Euglena accumulated carbohydrates and lipids under heterotrophic and phototrophic conditions. Although cellular lipid content increased, lipid as a percentage of dry weight was unaltered. Nitrogen deficient and sufficient heterotrophic cultures synthesized equal amounts of lipid per mole of exogenous carbon. Nitrogen deficiency does not alter the partitioning of available carbon between the synthesis of lipid and other cellular constituents but simply inhibits cell division so that the carbohydrate and lipid produced are divided among fewer cells increasing the quantity of storage products per cell. Cellular chlorophyll content decreased only when nitrogen deficient cells were maintained at high light intensities suggesting that chlorophyll loss is due to a reduction in the rate of resynthesis of chlorophyll destroyed through photooxidative damage. Anaerobiosis triggered lipid synthesis and promoted carbohydrate breakdown in the dark and light. Even after six days of nitrogen deficiency, anaerobiosis triggered additional lipid accumulation and carbohydrate breakdown. In contrast to nitrogen deficiency, anaerobiosis produced a preferential increase in the percentage of dry weight as lipid. This increase was due as much to a decrease in cellular dry weight as it was to the preferential utilization of available carbon for lipid synthesis. © 1988. The Japanese Society of Plant Physiologists