SEXUAL DEVELOPMENT IN THE HOMOTHALLIC GREEN-ALGA CHLAMYDOMONAS-MONOICA STREHLOW

Chlamydomonas monoica, cell division and mating are interdependent pro cesses, since under gametogenic conditions only newly born cells are m ating competent. By refeeding nitrogen-starved cells with nitrate or a mmonium ions, cell division and mating were synchronized. The mating c ompetence of the progeny cells was dependent on the amount of the nitr ogen source parent cells were refed, with an optimum around 0.1 mu mol . 10(5) cells. A second treatment with nitrate inhibited gametogenesi s, but only when applied during the first part of the cell cycle, sugg esting that an essential part of sexual development takes place during this period. During the latter part of the cell cycle, cells required light to acquire mating competence.