DETECTION AND EVALUATION OF AN INDUCER OF A DIFFUSIBLE MATING PHEROMONE OF THE HETEROTHALLIC CLOSTERIUM PERACEROSUM-STRIGOSUM-LITTORALE COMPLEX

When mating-type plus cells of the Closterium peracerosum-strigosum-li ttorale complex were incubated in nitrogen-deficient medium obtained f rom a 24-h-old mixed culture of mating-type plus and mating-type minus cells, protoplast-release-inducing activity specific for mating-type minus cells was detected in the medium. When mating-type plus cells we re incubated in the medium from a culture of exclusively mating-type m inus cells, protoplast-release-inducing activity was also detected. Th ese results suggested the existence of a substance, released from mati ng-type minus cells, that has the ability to make mating-type plus cel ls release protoplast-release-inducing protein (PR-IP). We designated it PR-IP Inducer. The PR-IP Inducer was constitutively released from m t(-) cells in the light. The PR-IP Inducer was heat-labile and had a r elative molecular weight of 10,000 on gel filtration. We suggest that the PR-IP Inducer is also a pheromonal substance that plays a role in the initial events in the sexual communication of this Closterium comp lex.