Repression of Chloroplast Development in Euglena gracilis by Substrates*

SYNOPSIS. Under “resting” conditions, synthesis of chlorophyll and alkaline fructose‐1,6‐diphosphatase in etiolated Euglena gracilis placed in light was repressed by metabolizable carbon sources. The degree of repression by any carbon source apparently depends on its rate of utilization by Euglena. Thus, pre‐adaptation of Euglena to a specific carbon source, e.g., glucose or ethanol, increased the repression of chloroplast synthesis in the light by that carbon source. Acetate and malate were not as repressive as ethanol. The similarity of this repression to the “glucose effect” is discussed.