| Abstract: | Sexual cell division (SCD) that produces two gametangial cells from one vegetative mother cell is the first step observed morphologically in the sexual reproduction in the Closterium peracerosum–strigosum– littorale complex. SCD‐inducing activities specific for each mating‐type cells were detected in the medium in which both mating type cells has been cocultured. Mating‐type minus (mt ? ) cells released SCD‐inducing substance specific for mating‐type plus (mt + ) cells and were designated as SCD‐ inducing pheromone (IP)‐minus, whereas mt ? specific substances released from mt + cells were designated as SCD‐IP‐plus. Culture medium was subjected to gel filtration, and then SCD‐IP‐plus and SCD‐IP‐minus chemical were found to have the molecular masses of 90–100 kDa and 10–20 kDa, respectively. It was evident that light was imperative for this type of signaling. Gametangial cells of both mating types were obtained from vegetative cells by treatment with SCD‐IPs. Gametangial mt + cells showed high competency for conjugation with vegetative mt ? cells, whereas gametangial mt ? cells showed low competency for conjugation with vegetative mt + cells. These results indicate that SCD in both mating type cells is induced by high molecular weight sex pheromones and that the roles of gametangial cells in the process of conjugation differ by sex. |
