Relationship between gametic differentiation and the cell cycle in the green alga Chlamydomonas eugametos

Summary: The relationship between the vegetative cell cycle and sexual competence in the green alga Chlamydomonas eugametos was studied using synchronized cultures. The gametic stage was found to be a regular part of the cell cycle; it extended from the beginning of the cell cycle to about 2 h prior to the commitment point for cell division. All variations in the length of this period caused by external growth conditions were accompanied by corresponding changes in the period of mating competence. The period varied depending on the fluence rate, temperature, and nitrate or CO2 concentration. We conclude that the length of the period in the cell cycle in which cells are mating competent is determined by the length of the precommitment period and that environmental factors do not influence mating competence directly, but rather affect the growth rate of the cells.