Ultrastructure of sporulation in the Hemiascomycetes Ascoidea corymbosa, A. rubescens, Cephaloascus fragrans, and Saccharomycopsis capsularis

Abstract

Sporulation in four species belonging to three different families of the Hemiascomycetes is described from serial sections. The results show that in each species the formation of the ascospore wall is initiated at a specialized spindle pole body. Spore delimitation proceeds concurrently with the last nuclear division in the ascus. The findings support the taxonomic position that these species belong to a group that includes the yeasts but that is distinct from the Euascomycetes.

A Cladistic Outline of the Eumycota

“…It occurs in the Hemiascomycetes (Curry, 1985: 401 ). This type of ascosporogenesis is reported for Dipodascopsis tothii (Curry, 1985: 410) and all other members of the Hemiascomycetes (Ashton andMoens, 1979: 1280), e.g. species of Saccharomyces, Ascoidea, Cephaloascus, and Saccharomycopsis (Ashton andMoens, 1979: 1259).…”

“…The two species Saccharomycopsis capsularis and Ascoidea corymbosa have uninuclear cells (Ashton and Moens, 1979) but it is not clear whether septal pores are present or not. 7.…”

“…(b) Ascus uesicle (coded 2). Ascosporogenesis involving an ascus vesicle is, according to Ashton andMoens (1979: 1259), a feature known only to the Euascomycetes and the Loculoascomycetes (Curry, 1985: 40 1 and references therein). The ascus vesicle is described as the formation ofa double membrane structure, at the periphery of the ascus.…”

The ultrastructure of ascosporogenesis in freeze-substituted Thelebolus crustaceus: enveloping membrane system and ascospore initial development

“…Beckett (4) argued that the terms prospore wall (3,42) and spore wall primordium (60) suggested that spore wall material was laid down between the double membranes before nuclear delimitation was completed; however, this sequence of events has not been shown to occur. He proposed the term spore-delimiting membrane (SDM) as an alternative.…”

“…Beckett (4) summarized the postulated origins, which included in Hemiascomycetes de novo synthesis in association with the NAO (3,6,25,42,43,59) as well as alternative modes (16,35,48,58), many of which could be interpreted as de novo synthesis or had inconclusive data. Taphrina deformans (51,52) was the only exception with the ascus plasma membrane as its apparent origin.…”