SUB DIVISION ASCOMYCOTINA
They are commonly called sac fungi or bladder fungi . They produce endogenously produced perfect state spores called ascospores . Higher members of ascomycotina show gradual degeneration of sex . Ascomycotina show physiological heterothallism . It is the male gamete of one mating type fertilizes the ascogonium of other mating type. Fruiting bodies are known as ascocarps which may be of following types -
1. Apothecium - It is cup like .example - Peziza
2. Perithecium - It is flask shaped . example - Claviceps .
3. Cleistothecium - It is globose and completely closed . Example - Aspergillus , Penicillium .
Some classes under sub division ascomycotina -
1. Hemiascomycetes
2. Plectomycetes
3. Pyrenomycetes
4. Discomycetes
Class Hemiascomycetes
One of the order of hemiascomycetes -
Endomycetales - yeast
Sachharomyces (Yeast )
Sub division - Ascomycotina
Class - Hemiascomycetes
Order - Endomycetales
Family - Sachharomycetaceae
Genus - Sachharomyces
Yeasts are of considerable importance therefore S. cerevisiae is commonly called bakers yeast or brewer yeast . They are rich source of proteins , vitamin B2 , enzymes invertase and zymase . Yeast is eukaryotic , unicellular and holocarpic ( whole cell transformed in reproductive structure ) . It has a large central vacuole . Cell wall is chiefly composed of chitin , polysachharides glucan , mannan ( cellulose is absent ) .
Vegetative reproduction in yeast takes place by budding , fission and endospores . Budding results in branched or unbranched chains of cells having appearance of pseudomycelium . Sexual reproduction in yeast takes place by gametangial coupulation in which two vegetative cells or two ascosores function as coupulating gametangia and fuse together to form zygote .Zygote develops into ascus which forms 4 / 8 ascospores . Three types of life cycles are recognised in yeasts -
1. Haplobiontic - Haplo phase is long . S. octosporus
2. Diplobiontic - Diplo phase is long . S. ludwigii
3. Haplo-diplobiontic - Both phases are long . S. cerevisiae