The response of wild type male gametes of allomyces to sirenin.

The hermaphroditic, haploid, sexual generation of the watermolds Allomyces macrogynus and A. arbuscula bear orange male gametangia and colorless female gametangia which discharge motile male and female gametes into an ambient liquid environment (1,8). The female gametes, beginning prior to their release from the gametangia, secrete sirenini, a sperm-attractant (3, 4), whose structure was recently established (6) and which is depicted in figure 1. The production of sirenin (7) was done with the almost entirely female isolate #F-1 (3) derived from a cross between A. macrogynus (n=28) and A. arbuscula (n=16) and the bioassay, during the time it was needed, with an almost entirely male isolate derived from the same cross. These particular hybrids have not been studied cytologically or genetically but the chromosome behavior of various crosses between the parents has been described (2). The purpose of this communication is to show that m-ale gametes from the parent species do respond chemotactically to sirenin which was synthesized by the female hybrid strain. At the same time, the experiments raise the possibility that there may be species-specific sirenins. The gametophytic generation of L. mnacrogynus, strain Burma 31 and A. arbuscula, strain iCeylon 1 were grown on Difco YpSs nutrient agar plates. Gametangia were scraped from these plates and placed in DS solution (3) in a small glass petri dish. Male gametangia were then picked up in a micro pipette and 500 placed in 0.6 nil of DS in containers of a proper size to take the assay apparatus (fig 2). Discharge of the gametes was then allowed to take place for 3 hours. The male gametangia must be separated in approximately 40 minutes, the time between immersion in DS solution and the first emergence of gametes. In this period it was possible to select 1500 gametangia thus per-