Basidomycetes

Basidomycetes are a fungal group belonging to the Eukarya domain, which includes all life forms composed by nucleated cells. Basidomycetes are classified under the Fungi kingdom as belonging to the phylum –mycota (i.e., Basidomycota or Basidiomycota), class –mycetes (i.e., Basidomycetes). Fungi are frequently parasites that decompose organic material from their hosts, such as those growing on rotten wood, although some may cause serious plant diseases such as smuts (Ustomycetes) and rusts (Teliomycetes). Some live in a symbiotic relationship with plant roots (Mycorrhizae). A cell type termed basidium is responsible for sexual spore formation in Basidomycetes, through nuclear fusion followed by meiosis, thus forming haploid basidiospores. Fungi pertaining to the Basidomycota phylum may present dikaryotic hyphae , i.e., walled filamentous cylindrical structures resembling branches that are formed when the two nuclei in the apical cell of a hypha divide simultaneously. One divides in the hyphal main axis and the other into the clamp, thus giving origin to a temporary monokaryotic clamp cell that is then fused to the sub apical cell, restoring the dikaryotic status. Spores are lined next to one another on the several neighboring basidia that form the Hymenium on the mushroom gill. Each spore usually bears the haploid product of meiosis. In adverse conditions, the spores may remain dormant for long periods, from months to years. When conditions are favorable, the spores germinate into uninucleated hyphae, forming monokaryotic mycelia. A dikaryotic mycelium is formed as the result of the fusion of two monokaryotic mycelia. Basidomycetes' sexual spores are more often than not disseminated through the wind, either by passive or forced spore discharge.

Basidomycetes comprises over 15,000 species, belonging to 15 different orders, most of them wood-rotting species. Some examples of Basidomycetes are as follows: Coral Fungus or Ramaria, pertaining to the Hymeniales order; Stinkhorn or Phallus, from the Phallales order; Corn smut or Ustilago, from the Ustilaginales order; Puffball or Lycoperdon, from the Lycoperdales order; White Button Pizza or Agaricus bisporus, from the Agaricales order.

The cell walls of fungi contain distinct layers, mainly constituted by chitin and not by cellulose. Multicellular fungi such as mushrooms have their vegetative bodies constituted mainly by filamentous hyphae. As parasites, Basidomycota and other fungi phyla (i.e., Chytridiomycota, Zygomycota, Ascomycota), do not itlize photosynthesis , and therefore, lack clorophyll. They produce instead several different exoenzymes, which are released directly on their hosts through invading filaments that can reach the target substance to be enzymatically decomposed. The exoenzymes are utilized in the digestion of the available organic substance from which they absorb micronutrients to synthesize and store great amounts of glycogen, whereas plants store energy under the form of starch. They also contain in their cell membranes ergosterol, a sterol found exclusively in fungi.

See also Chitin; Eukaryotes; Fungal genetics; Mycology