Commitment to autogamy in Paramecium blocks mating reactivity: implications for regulation of the sexual pathway and the breeding system.

Commitment to autogamy blocks mating reactivity in Paramecium. Cells which had previously developed mating reactivity, lost reactivity 30-90 min prior to the preautogamous fission. Mating reactivity develops at a standard level of starvation when cells are allowed to exhaust their food supply naturally. In abruptly starved cultures, mating reactivity appears 3.3 h after downshift. Autogamy is also triggered by starvation. The level of starvation required for initiation of autogamy decreases progressively as cells age. When the autogamy starvation threshold drops to such a low level that all cells become committed to autogamy before any of them develop mating reactivity, reactivity does not occur under natural starvation conditions and the period of maturity for conjugation has come to an end. There is no absolute immature period for autogamy.