CHARACTERIZATION OF THE CELL-CYCLE IN SYNCHRONOUS CULTURES OF CHLAMYDOMONAS-EUGAMETOS IN RELATION TO GAMETOGENESIS

The cell cycle of Chlamydomonas eugametos was synchronized at low cell densities by growing cells under conditions of alternating light and dark periods. Synchronization of the cell cycle was demonstrated by determining cell size, cytokinesis, and release of daughter cells. The microscopic data were in agreement with the accumulation patterns of mRNAs for ribulose bisphosphate carboxylase/oxygenase small subunit, histone H4 and beta-tubulin. Cells of C. eugametos secrete a sticky material which enables cells to adhere to a solid substrate during cell division. The secretion of this material was also cell-cycle-regulated and preceded cytokinesis. Recently, it was reported that in synchronous exponential-phase cultures of high cell densities, young daughter cells temporarily behave like gametes during the cell cycle. However, under our growth conditions this was not observed. First, daughter cells did not agglutinate with normal gametes of the opposite mating type. Second, extraction of growing cells did not release any agglutinin activity as measured both by an in vitro agglutination assay and by an agglutinin-specific monoclonal antibody. We conclude therefore that gametogenesis in C. eugametos is not necessarily a normal phase of the cell cycle.