A hypha consists of one or morecells surrounded by a tubularcell wall. In most fungi, hyphae are divided into cells by internal cross-walls called "septa" (singularseptum). Septa are usually perforated by pores large enough forribosomes,mitochondria, and sometimesnuclei to flow between cells. The major structural polymer in fungal cell walls is typicallychitin, in contrast to plants andoomycetes that havecellulosic cell walls. Some fungi have aseptate hyphae, meaning their hyphae are not partitioned by septa.
Hyphae grow at their tips. During tip growth, cell walls are extended by the external assembly andpolymerization of cell wall components, and the internal production of new cell membrane.[3] TheSpitzenkörper is an intracellular organelle associated with tip growth. It is composed of an aggregation of membrane-bound vesicles containing cell wall components. The Spitzenkörper is part of theendomembrane system of fungi, holding and releasingvesicles it receives from theGolgi apparatus. These vesicles travel to the cell membrane via thecytoskeleton and release their contents (including various cysteine-rich proteins includingcerato-platanins andhydrophobins)[4][5] outside the cell by the process ofexocytosis, where they can then be transported to where they are needed. Vesicle membranes contribute to growth of the cell membrane while their contents form new cell wall. The Spitzenkörper moves along theapex of the hyphal strand and generates apical growth and branching; the apical growth rate of the hyphal strand parallels and is regulated by the movement of the Spitzenkörper.[6]
As a hypha extends,septa may be formed behind the growing tip to partition each hypha into individual cells. Hyphae can branch through the bifurcation of a growing tip, or by the emergence of a new tip from an established hypha.
The direction of hyphal growth can be controlled by environmental stimuli, such as the application of an electric field. Hyphae can also sense reproductive units from some distance, and grow towards them. Hyphae can weave through a permeable surface to penetrate it.[3]
Hyphae may be modified in many different ways to serve specific functions. Someparasitic fungi formhaustoria that function in absorption within the host cells. Thearbuscules ofmutualisticmycorrhizal fungi serve a similar function in nutrient exchange, so are important in assisting nutrient and water absorption by plants.Ectomycorrhizal extramatrical mycelium greatly increases the soil area available for exploitation by plant hosts by funneling water and nutrients toectomycorrhizas, complex fungal organs on the tips of plant roots. Hyphae are found enveloping thegonidia inlichens, making up a large part of their structure. In nematode-trapping fungi, hyphae may be modified into trapping structures such as constricting rings and adhesive nets.Mycelial cords can be formed to transfer nutrients over larger distances. Bulk fungal tissues, cords, and membranes, such as those of mushrooms andlichens, are mainly composed offelted and oftenanastomosed hyphae.[7]
Non-septate hyphae are associated withMucor,[9] somezygomycetes, and other fungi.
Pseudohyphae are distinguished from true hyphae by their method of growth, relative frailty and lack ofcytoplasmic connection between the cells.
Yeasts form pseudohyphae.[10] They are the result of a sort of incompletebudding where the cells elongate but remain attached after division. Some yeasts can also form true septate hyphae.[11]
Classification based on cell wall and overall form
Characteristics of hyphae can be important in fungal classification. Inbasidiomycete taxonomy, hyphae that comprise thefruiting body can be identified as generative, skeletal, or binding hyphae.[12]
Generative hyphae are relatively undifferentiated and can develop reproductive structures. They are typically thin-walled, occasionally developing slightly thickened walls, usually have frequent septa, and may or may not haveclamp connections. They may be embedded in mucilage or gelatinized materials.
Skeletal hyphae are of two basic types. The classical form is thick-walled and very long in comparison to the frequently septate generative hyphae, which are unbranched or rarely branched, with little cell content. They have few septa and lack clamp connections. Fusiform skeletal hyphae are the second form of skeletal hyphae. Unlike typical skeletal hyphae these are swollen centrally and often exceedingly broad, hence giving the hypha afusiform shape.
Binding hyphae are thick-walled and frequent branched. Often they resemble deer antlers or defoliated trees because of the many tapering branches.
Based on the generative, skeletal and binding hyphal types, in 1932E. J. H. Corner applied the terms monomitic, dimitic, and trimitic to hyphal systems, in order to improve the classification ofpolypores.[13][14]
Every fungus must contain generative hyphae. A fungus which only contains this type, as do fleshy mushrooms such asagarics, is referred to asmonomitic.
If a fungus contains the obligate generative hyphae (as mentioned in the last point, "every fungus must contain generative hyphae") and just one of the other two types (either skeletal or binding hyphae), it is calleddimitic. In fact dimitic fungi almost always contain generative and skeletal hyphae; there is one exceptional genus,Laetiporus that includes only generative and binding hyphae.
Skeletal and binding hyphae give leathery and woody fungi such aspolypores their tough consistency. If a fungus contains all three types (example:Trametes), it is calledtrimitic.
Fungi that formfusiform skeletal hyphae bound by generative hyphae are said to havesarcodimitic hyphal systems. A few fungi form fusiform skeletal hyphae, generative hyphae, and binding hyphae, and these are said to havesarcotrimitic hyphal systems. These terms were introduced as a later refinement by E. J. H. Corner in 1966.[15]
Hyphae are described as "gloeoplerous" ("gloeohyphae") if their high refractive index gives them an oily or granular appearance under the microscope. These cells may be yellowish or clear (hyaline). They can sometimes selectively be coloured by sulphovanillin or other reagents. The specialized cells termedcystidia can also be gloeoplerous.[16][17]
^Klatt, Edward C."Mucormycosis".WebPath. University of Utah School of Medicine. Retrieved10 December 2008.
^Reiss, Errol; DiSalvo, Art (31 May 2018). "Yeasts". In Hunt, Richard (ed.).Microbiology and Immunology On-line. University of South Carolina. Retrieved20 November 2020.
^Sudbery, Peter; Gow, Neil; Berman, Judith (2004). "The distinct morphogenic states ofCandida albicans".Trends in Microbiology.12 (7):317–324.doi:10.1016/j.tim.2004.05.008.PMID15223059.
^"Hyphal System". Illinois Mycological Association. Archived fromthe original on 2006-10-14. Retrieved2007-02-11.
