Periodic zoospore production by Protosiphon botryoides under alternating light-dark periods.

The effect of light-dark periods, of 24 hr or longer complete cycle, on time of zoospore production by Protosiphon botryoides KMebs was investigated in unstirred flask cultures and in stirred cultures supplied 1 % C02 in air. Synchronized zoospore production was observed in both types of cultures. In stirred cultures supplied 1% C02 a light-dark cycle of 36-12 hr gave better synchrony than did a cycle of 12-12 or 60-12 hr. Illumination by cool-white fluorescent bulbs inhibited zoospore formation strongly, possibly by inhibiting cytoplasmic cleavage in parent cells. Darkness, in comparison to illumination, promoted the formation of zoospores, and their synchronous production under alternating light-dark cycles occurred as a consequence.