A STUDY OF LIGHT INTENSITY, PERIODICITY, AND WAVELENGTH ON ZOOSPORE PRODUCTION BY PROTOSIPHON BOTRYOIDES KLEBS(1) (2)

When mature Protosiphon cells were placed in darkness, zoospore production was more extensive and was completed in a shorter time at a temperature of 27 C than at 22 or 15 C. Cool-white fluorescent (Sylvania) light inhibited the process measurably at a radiation intensity of 0.6±10(3) ergsjcm(2) -sec; inhibition was 96% complete at 14±10(3) ergs/cm(2) -sec. For mature cells previously grown under repeated 12-12 hr light-dark cycles, a dark period of approximately 2 hr at 22 C allowed cell division to proceed to a stage such that reillumination did not inhibit continued development of zoospores. Monochromatic light from 402 to approximately -494 nm, as compared to darkness, inhibited zoospore formation; maximal inhibition was at 432-461 nm. In contrast, monochromatic light from 522 to 726 nm stimulated zoospore formation relative to darkness. Synchronous zoospore production was obtained using the following regimes: (A) 12 hr cool-white alternated with 12 hr yellow, (B) 12 hr cool-white alternated with 12 hr blue. Under regime A synchronous zoospore release (following synchronous production) occurred near the end of the yellow irradiation period, while under regime B it occurred near the end of the cool-white irradiation period. The significance of this in terms of photoprocesses and possible photoreceptors is discussed.