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An ascus (from Ancient Greek ἀσκός (askós) 'skin bag, wineskin'; pl.: asci) [1] is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division.
Ascomycota is a monophyletic group (containing all of the descendants of a common ancestor). Previously placed in the Basidiomycota along with asexual species from other fungal taxa, asexual (or anamorphic ) ascomycetes are now identified and classified based on morphological or physiological similarities to ascus-bearing taxa , and by ...
After formation of the ascus-initial cell, the ‘A’ and ‘a’ nucleus fuse with each other to form a diploid nucleus (see figure, top of §). This nucleus is the only diploid nucleus in the entire life cycle of N. crassa. The diploid nucleus has 14 chromosomes formed from the two fused haploid nuclei that had 7 chromosomes each.
This binuclear cell initiates ascus formation and is called an "ascus-initial" cell. Next the two uninucleate cells on either side of the first ascus-forming cell fuse with each other to form a binucleate cell that can grow to form a further crozier that can then form its own ascus-initial cell. This process can then be repeated multiple times.
Trichophyton concentricum reproduces sexually via its ascospores which are produced internally in vacuoles called asci (sing. ascus), found in pouches known as ascomata (sing. ascoma). [4] The asexual form of T. concentricum is composed of irregularly arranged filaments with chlamydoconidia and microaleurioconidia. [5]
Rocks and soil are the most common substrates for the Verrucariaceae, with growth on wood, bark, and leaves less common. Several species are components of biological soil crusts and contribute to the formation and stabilisation of soil. Some semi-aquatic lichens occur in this family, including about two dozen species of marine lichens.
Drechsler found that graminicolous forms of Helminthosporium produced teleomorphs with characteristic features of greater ascus and ascospore width as well as helicoid ascospores with bipolar germination, which deviates from previously described characters of Ophiobolus.
An ascocarp, or ascoma (pl.: ascomata), is the fruiting body of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores.