Structural and developmental aspects of cycloheximide effects on the chloroplasts of Euglena gracilis

Abstract

Low concentrations of cycloheximide (6 μg/ml) inhibited cell division of Euglena gracilis. Chlorophyll content and the ability of the cells to form colonies, however, were unaffected. Higher concentrations (10–20 μg/ml) were lethal. In dark-grown cells exposed to light in the presence of 8 μg/ml cycloheximide, cell division stopped but the transformation of proplastids into chloroplasts (greening) was only partially affected. Greening of dark-grown non-dividing cells exposed to light in the presence of cycloheximide was inhibited proportionally to the concentration of the drug. With the highest concentration used (20 μg/ml) no chlorophyll was synthesized and the transformation of proplastids to chloroplasts was prevented.It was concluded in accordance with previous suggestions that cycloheximide affects the plastids through its effect on the cytoplasm and that the inhibition of chlorophyll synthesis is due to prevention of thylakoid formation.