Microspectrophotometric and genetic analysis of heteroploidy in the myxomycete Didymium iridis

Abstract

Microspectrophotometric and nuclear marker analyses were made of the chromosome distribution patterns in all life cycle stages for polyploid-haploid crosses in Didymium iridis over a period of four filial generations. Data was collected from swarmer, myxamoeba, plosmodia, and sporangial stages of the life cycle. Relative ploidy determinations of nuclear DNA contents were provided by cyrophotometric measurements of Feulgen-DNA nucleal reaction nuclei. Mating type marker genetics also provided information on chromosome segregation in meiospores.

The results of the investigation indicates the production of plasmodia and meisopores with a variety of unexpected ploidy levels. Cytological examinations of progeny spores suggest that polyploid nuclei undergo meiotic stress and produce aneuploid myxamoeba. Genetic analysis of these myxamoeba indicates the production and transmission of progeny clones capable of expressing both parental mating types. The further observation of selfing myxamoeba suggests that in this system : chromosome elimination after karyogamy of parental nuclei occurs and, a nuclear gene, gene product or, cytoplasmic factor has established a condition of enhanced cell fusion through the ability to institute membrane contact. It is yet to be determined if this behavior has a relationship to the production of aneuploid spores, however, cytoplasmic inheritance of the factors(s) involved is implicated.