A Study of Ascus Developmental Fine Structure in Eleutherascus Peruvianus Huang With Special Reference to Ascospore Ontogeny.
Date of Award
Doctor of Philosophy (PhD)
Eleutherascus is an enigmatic ascomycete genus with some structural features common to both the Eurotiales and Pezizales. It lacks a peridium and paraphyses and typically produces an ascocarp consisting of only one or two asci and some sterile hyphae. The life cycle of E. peruvianus was studied by electron and optical microscopy. The principle events that culminate in ascospore production and germination are described and compared to their equivalents in some purportedly related species. Ascogenesis is initiated through crozier development in a manner similarly described in many Discomycetes. Additionally, a specialized septal pore cap structure (which appears structurally equivalent to that described exclusively in Discomycetes) becomes evident early in development. Meiosis produces an eight-nucleate ascus with nuclei evenly distributed throughout the cytoplasm by the apparently consistent spindle orientations of the three divisions. The possible relationship of early nuclear behavior to ultimate ascospore orientation is discussed. The nuclear products of meiosis become surrounded by the double-membrane ascus vesicle in a manner nearly universal among Euascomycetes--by the direct involution of the ascus plasmalemma, and not by any of the mechanisms more commonly ascribed to Discomycetes. Evidence suggests cytoplasmic microtubules are involved in ascospore delimitation. E. peruvianus initially deposits a thick, electron transparent, unstructured primary wall. This is immediately followed by the deposition of a secondary wall at varying rates over the surface of the primary wall through the activity of the epiplasm. The appearance of complex membranous connections between adjacent ascospores, and the deposition of secondary wall material along these sites is suggested as the mechanism for the formation of the ascospore brims and the resultant appearance of orderly arrangements of the spores within the ascus. Germination is by a rupture of the spore wall and the emergence of a germ tube which is derived de novo beneath the spore wall layers. Cytological and cytochemical evidence favor the notion that the spore wall is partially resorbed by the germinating sporoplast.
Steffens, Walstine Lon III, "A Study of Ascus Developmental Fine Structure in Eleutherascus Peruvianus Huang With Special Reference to Ascospore Ontogeny." (1981). LSU Historical Dissertations and Theses. 3701.