Evidence for a plasma membrane mating receptor in the myxomycete Didymium iridis.

Haploid isolates Panamanian 2-7A8 and Honduran 1-2A1 of the heterothallic myxomycete Didymium iridis were investigated in order to determine whether membrane mating factors or receptors were present and necessary in order that cell fusion could occur and zygote formation take place. Haploid and diploid controls grown on half strength cornmeal media, and experimental crosses grown on the same media plus concanavalin A, were analysed by quantitative cytophotometry employing the Feulgen nuclear reaction. Nuclear DNA analysis demonstrated that Con A treated cells when crossed did not produce zygotes or plasmodia, while those left untreated did so almost all of the time. On rare occasion plasmodia did develop in treated cultures (1.8% or two out of 110). These plasmodia demonstrated low viability and upon analysis were shown to be haploid. It was concluded that they had developed by apogamy, and therefore did not require plasma membrane bound mating receptors, cell fusion, or zygote formation.