ANALYSIS OF GAMETIC PROTOPLAST RELEASE IN THE CLOSTERIUM-PERACEROSUM-STRIGOSUM-LITTORALE COMPLEX (CHLOROPHYTA)

A biologically active glycoprotein (protoplast-release-inducing protein; PR-IP), which induces the release of gametic protoplasts from mating type minus (mt-) cells of the Closterium peracerosum-strigosum-littorale complex, was prepared from a medium in which mt- and mt+ cells had been previously incubated together. The process of PR-IP-inducing protoplast release was analyzed. Induction of protoplast release was dependent upon the duration of both PR-IP treatment and preincubation in nitrogen-deficient mating medium before PR-IP treatment. Low cell density in the preculture stage had a significant stimulative effect upon the induction of protoplast release. Light was necessary for protoplast release, especially just before PR-IP treatment. Chloramphenicol and 3-(4-chlorophenyl)-1,1-dimethylurea (CMU) exerted inhibitory effects on protoplast release, especially when they were applied to the preculture stage but not when they were applied to the protoplast-releasing stage after the PR-IP treatment. We suggest that preculture at a low cell density under continuous light conditions that may cause metabolic changes in the chloroplast is a very important stage for gametic protoplast release in this Closterium.