Physiological characterization of the sex pheromone protoplast-release-inducing protein from the Closterium peracerosum-strigosum-littorale complex (Charophyta)

In the unicellular charophycean alga Closterium peracerosum-strigosum-littorale complex, the protoplast-release-inducing protein (PR-IP), a sex pheromone responsible for gametic protoplast release from mating-type minus (mt(-)) cells, was found to stimulate secretion of mucilage from the cells. Induction of sexual cell division by PR-IP was also confirmed. Bioassays were used to determine the minimum doses required to induce these functions, revealing that 5 . 10(-16) M of PR-IP stimulated mucilage secretion, and that 5 . 10(-10) M of PR-IP were required for protoplast release. Exposure of the cells to 5 . 10(-11) M of PR-IP resulted in the induction of sexual cell division as well as mucilage secretion. These results strongly suggest that PR-IP is a multifunctional pheromone that independently promotes multiple steps in conjugation at the appropriate times through different induction mechanisms.