Mitosis in the yeast phase of the basidiomycetes Bensingtonia yuccicola and Stilbum vulgare and its phylogenetic implications.

Phylogenetic studies of yeasts rely on an extensive molecular and biochemical data set, but structural characters are scarce. Details of mitosis in yeasts have been studied with transmission electron microscopy and immunofluorescence. Of these two methods immunofluorescence is faster and easier and yields sufficient detail for cytological comparisons. Only three basidiomycetous yeasts have been studied thus far with immunofluorescence. Mitosis in budding cells of ascomycetous yeasts occurs in the parent, while in basidiomycetous yeasts, except in Agaricostilbum pulcherrimum, it occurs in the bud. Mitosis in additional yeasts in the Agaricostilbomycetidae of the Urediniomycetes was observed using immunofluorescence localization of freeze-substituted material. In Stilbum vulgare, mitosis occurred in the parent, but in Bensingtonia yuccicola it occurred in the bud as in most other basidiomycetous yeasts. Stilbum vulgare also had predominantly binucleate yeast cells. Nuclear small subunit rDNA sequence data showed that A. pulcherrimum and S. vulgare are more closely related to each other than to B. yuccicola within the Agaricostilbomycetidae. Based on the few taxa examined, mitotic and cytoskeletal characters provide phylogenetic information.