Light Conditions for Sexual Reproduction in Heterothallic Strains of Closterium

Sexual reproduction in heterothallic strains of Closterium peracerosum-strigostan-littorale,KAS-4-29 (mating type minus) and KAS-4-30 (mating type plus),depended on a light intensity higher than 3,000 lux. Two kindsof cell division occurred in the mating medium: 1) one kindoccurred at low light intensity (less than 1,000 lux) and wasnot linked to conjugation, and 2) a sexual one occurred at highlight intensity (higher than 3,000 lux) and was linked to conjugation.3-(4-Chlorophenyl)-l,l-dimethylurea at 1 µM added at thebeginning of the mating culture completely inhibited conjugationbut not cell division. Chloramphenicol at 20 to 40 µg/mladded at the beginning of the culture inhibited conjugationcompletely and cell division partly. The drugs added after 12h of the mating culture did not inhibit the division processes.Varying light intensity after 12 h of culture did not affectsexual activity. The photosynthetic activity was highest inthe cells at the beginning of the mating culture, and then markedlydecreased. The data indicate that the early period of the matingprocess depends strictly on the light conditions. (Received March 12, 1982; Accepted November 30, 1982)