Studies on the vegetative life cycle ofChlamydomonas reinhardiDangeard in synchronous culture II. Effects of chloramphenicol and cycloheximide on the length of cell cycle

摘要

Cells ofChlamydomonas reinhardiDangeard were synchronously grown under a 12 hr light—12 hr dark regime. When these cells were brought into contact with chloramphenicol for a short period at early stages in the cell cycle, zoospore liberation was delayed for a period which was nearly the same as that of the duration of contact with the antibiotic. When given at later stages, the antibiotic caused no such effect. Cycloheximide, on the other hand, caused—when provided at some intermediate stage of the cell cycle—two different prolonging effects on the length of the cell cycle: one doubled the normal length (observed when the drug was administered at certain stages) and the other caused a delay similar to that caused by chloramphenicol. Interestingly, no prolonging effect was observed when cycloheximide was given either at early stages or at later stages, such as during the last 1/4 period of the cell cycle preceding zoospore liberation. Based on these results, three phases were distinguished in the algal cell cycle:“chloramphenicolsensitive”,“cycloheximide-sensitive”and“insensitive”phases. Considering the known facts about the modes of action of the two antibiotics inhibiting protein synthesis, discussions were made on the significance of protein synthesis in chloroplasts and in cytoplasm in determining the length