Septum (mycology)

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A septum (plural: septa ) or septum (plural: septa ) is a septum in the hyphae , basidia , cystidia, and spores and conidia of fungi . The tube walls (disseptiments) of the fruit layer (hymenophore) of pore and tube fungi are also called septa. They form part of the hyphae wall. In spores and basidia, a distinction is made between longitudinal (in the longitudinal direction) and transversal septa (transverse to the longitudinal axis). There may be buckles on the septa of hyphae .

After the nucleus has been divided, septa arise from the hyphae wall and expand inwards. A porus remains in the middle through which the cytoplasm and organelles can pass. Some fungi, such as the yoke and arbuscular mycorrhizal fungi , do not form septa in their hyphae and are therefore referred to as aseptic or coenocytic .

Primary and secondary septa

Septa that arise between the daughter cells after a nucleus division is also called primary septa . Secondary septa arise when old, more or less empty areas of hyphae, basidia, cystidia or spores are separated from living parts filled with plasma and cell nucleus. Secondary septa are thin and often arched.

Comparison with the cell wall of plants

The septa of the fungi resemble the cell walls of plants and (in many cases also morphologically similar) algae , but differ from these in essential points. After the nucleus division, the plant cell wall is deposited in reverse, progressively from the inside to the outside (cf. phragmoplast ). It therefore has no porus, but only much narrower plasmodesmata , which only allow a limited exchange of soluble substances. While the cytoplasm in fungal hyphae, even if they are septated, represents a continuum within the hypha or an extensive hyphae network and including the organelles can move more or less freely within the scope of the plasma flow , organelles and the plasma flow in plants remain open limited to one cell each.