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Home >> Microbiology >> Eukarya Eukaryotic-Microorganisms >> Reproduction of Yeasts

Reproduction

(i) Asexual Reproduction

Budding. Budding is the most common method of asexual reproduction in yeasts. In this process, a tube is sent out from the nuclear vacuole adjacent to the parent cell nucleus toward a point of the cell wall nearest the vacuole.

There a small protuberance develops as a result of a local weakening of the existing cell wall. The tube then passes into the protuberance, the developing bud, which enlarges and is filled with nuclear and   cytoplasmic material from the parent.

When the bud matures and is nearly as large as the parent, a cross wall is formed which separates   the daughter from the mother although the two may remain attached, and the buds themselves may give rise to daughter buds in chains.

§ This chain of cell looks like a mycelium and hence is called m 'pseudomycelium'.

However, the separated mother cells have convex bud-scars whereas the daughter cells have concave birth-scars.

During its life time, a mature yeast cell may produce, by budding, an average of 24 daughter cells Since bud  are always  produced at different places on the cell surface, one can count the number of budscars on it.

Budding

Budding



Binary fission. Some yeasts (e.g., Schizosaccharomyces) produce asexually by binary fission, a process akin to that by which most of the bacteria reproduce.

The yeast cell swells or elongates, the nucleus divides. Like budding, cells may divide by separating so that chains of cells, the pseudomycelia, are produced.

(ii) Sexual Reproduction

Sporulation is the usual method of sexual reproduction in yeasts and results in the production of ascospores.

Sexual union in the yeasts takes place either between two vegetative cells between two ascospores, that assume the function of copulating gametangia, unite and form a zygote cell.

Eventually, an ascus is formed and that contains ascospores, their number depending on the number of nuclear divisions that take place and on the subsequent development of the nuclei.

Four or eight ascospores per ascus is the usual number, but other numbers also may be encountered. The ascospores formed by the yeasts are often globose or ovoid.

 

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