Read this article to learn about Schizosaccharomyces Octosporus and Saccharomycodes Ludwigii !
The somatic cells of S. octosporous are haploid. It undergoes asexual cycle called fission during favorable condition and haplobiontic sexual cycle.
In this method, the mother cell elongates, its nucleus divides through intranuclear spindle formation to produce two daughter nuclei.
A transverse septum is laid centripetally dividing the mother cell into two daughter cells.
(b) Haplobiontic cycle:
In this type of life cycle the somatic cells are haploid and are well represented, but diploid phase is represented by zygote which is very short. During unfavorable period the somatic cells come in contact and starts conjugation. The two conjugating cell fuse to form a diploid zygote cell which acts as an ascus. The zygote undergoes meiosis followed by mitosis to produce eight ascospores. The ascospores on liberation grow into somatic cells (Fig. 6.12).
Life cycle of Saccharomycodes ludwigii:
In case of S. ludwigii, somatic cells are diploid (2n). They reproduce asexually by both budding and fission while their sexual cycle is diplobiontic.
In this type of life cycle each diploid somatic cell directly functions as ascus and produces four haploid ascospores. The ascospores are the only haploid phase of the life cycle. Inside the ascus, ascospores fuse in pairs to form two diploid cells. Each diploid cell germinates by a germ tube pierce the ascus wall and acts like a sprout mycelium. The diploid somatic cells develop by budding from it.
In addition to the above given methods of sexual reproduction the following methods are found:
Copulation between two adjoining sister cells. This is isogamous and the cells which fuse do not separate after fission but remain united to form short chains.
Copulation between mother and the daughter cell formed by budding. The daughter remains attached to the mother and the nucleus of the bud migrates into the mother. An outgrowth develops at the opposite end of the mother.
Both the nuclei more into this and fuse. The fusion nucleus undergoes two divisions one being reduction division. Of the four nuclei formed three degenerate and the ascospore is formed around only one. Thus it is a type of anisogamous type of reproduction and occurs in Zygo- saccharomyces chevalieri.
In this, asci are formed without actually involving copulation of two cells.