Basidium

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Diagram showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins. Basidium schematic.svg
Diagram showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins.

A basidium (pl.: basidia) is a microscopic spore-producing structure found on the hymenophore of reproductive bodies of basidiomycete fungi. The presence of basidia is one of the main characteristic features of the group. These bodies are also called tertiary mycelia, which are highly coiled versions of secondary mycelia. A basidium usually bears four sexual spores called basidiospores. Occasionally the number may be two or even eight. Each reproductive spore is produced at the tip of a narrow prong or horn called a sterigma (pl. sterigmata), and is forcefully expelled at full growth.

Contents

The word basidium literally means "little pedestal". This is the way the basidium supports the spores. However, some biologists suggest that the structure looks more like a club. A partially grown basidium is known as a basidiole.

Structure

Most basidiomycota have single celled basidia (holobasidia), but some have ones with many cells (a phragmobasidia). For instance, rust fungi in the order Puccinales have phragmobasidia with four cells that are separated by walls along their cross section. Some jelly fungi in the order Tremellales also have phragmobasidia with four cells that are separated by walls and are shaped like a cross. Sometimes the basidium develops from a probasidium, which is not elongated like a typical hypha. The basidium may be stalked or attached directly to the hyphae.

The basidium is normally club-shaped: narrow at the stem and wide near its outer end. It is widest in the middle hemispherical dome at its apex, and its base is about half the size of the widest diameter at the highest point. Basidia with a short and narrow base are shaped like an inverted egg, and occur in genera such as Paullicorticium , Oliveonia , and Tulasnella . Basidia with a wide base are often shaped like a barrel. [1]

How basidiospores are expelled

In most basidiomycota, the basidiospores are forcibly expelled. The propulsive force is derived from a sudden change in the center of gravity of the discharged spore. Important factors in forcible discharge include Buller's drop, a drop of fluid that builds up at the nearer tip (hilar appendage) of each basidiospore; the offset attachment of the spore to the extending narrow prong, and the presence of hygroscopic regions on the basidiospore surface. Basidiospore discharge can only succeed after sufficient water vapor has condensed on the spore.

When a basidiospore matures, sugars present in the cell wall begin to serve as condensation loci for water vapour in the air. Two separate regions of condensation are critical. At the pointed tip of the spore (the hilum) closest to the supporting basidium, Buller's drop builds up as a large, almost spherical water droplet.

03 01 04 discharge of ballistospore (M. Piepenbring).png

At the same time, condensation occurs in a thin film on the stalk-facing part of the spore. When these two bodies of water combine, the release of surface tension and the sudden change in the center of gravity suddenly expels the basidiospore. Remarkably, the initial acceleration of the spore is estimated to be about 10,000  g. [2]

Evolutionary loss of expulsion by force

Some basidiomycetes do not have a means to forcibly expel their basidiospores, although they still form them. In each of these groups, spore dispersal occurs through other means of expulsion.

For example:

In these cases the basidiospore typically lacks a hilar appendage, and expulsion by force does not occur. Each example is thought to represent an independent evolutionary loss of the forcible discharge that comes before all basidiomycetes.

Related Research Articles

<span class="mw-page-title-main">Basidiomycota</span> Division of fungi

Basidiomycota is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basidiomycota includes these groups: agarics, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and Cryptococcus, the human pathogenic yeast.

The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in others some cells develop into sterile cells called cystidia (basidiomycetes) or paraphyses (ascomycetes). Cystidia are often important for microscopic identification. The subhymenium consists of the supportive hyphae from which the cells of the hymenium grow, beneath which is the hymenophoral trama, the hyphae that make up the mass of the hymenophore.

<span class="mw-page-title-main">Heterobasidiomycetes</span> Class of fungi

Heterobasidiomycetes, including jelly fungi, smuts and rusts, are basidiomycetes with septate basidia. This contrasts them to homobasidiomycetes, including most mushrooms and other Agaricomycetes, which have aseptate basidia. The division of all basidiomycetes between these two groups has been influential in fungal taxonomy, and is still used informally, but it is no longer the basis of formal classification. In modern taxonomy homobasidiomycetes roughly correspond to the monophyletic class Agaricomycetes, whereas heterobasidiomycetes are paraphyletic and as such correspond to various taxa from different taxonomic ranks, including the Basidiomycota other than Agaricomycetes and a few basal groups within Agaricomycetes.

<span class="mw-page-title-main">Basidiospore</span> Reproductive structure of a fungus

A basidiospore is a reproductive spore produced by basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. Typically, four basidiospores develop on appendages from each basidium, of which two are of one strain and the other two of its opposite strain. In gills under a cap of one common species, there exist millions of basidia. Some gilled mushrooms in the order Agaricales have the ability to release billions of spores. The puffball fungus Calvatia gigantea has been calculated to produce about five trillion basidiospores. Most basidiospores are forcibly discharged, and are thus considered ballistospores. These spores serve as the main air dispersal units for the fungi. The spores are released during periods of high humidity and generally have a night-time or pre-dawn peak concentration in the atmosphere.

<i>Stereum sanguinolentum</i> Species of fungus

Stereum sanguinolentum is a species of fungus in the Stereaceae family. A plant pathogen, it causes red heart rot, a red discoloration on conifers, particularly spruces and Douglas-firs. Fruit bodies, which are produced either on dead wood or on dead branches of living trees, form a thin leathery crust on the wood surface. Fresh fruit bodies will bleed a red-colored liquid if injured, reflected in the common names bleeding Stereum or the bleeding conifer parchment. It can be the host of the parasitic jelly fungus Naematelia encephala

<span class="mw-page-title-main">Agaricomycotina</span> Subdivision of fungi

Agaricomycotina is one of three subdivisions of the Basidiomycota, and represents all of the fungi which form macroscopic fruiting bodies. Agaricomycotina contains over 30,000 species, divided into three classes: Tremellomycetes, Dacrymycetes, and Agaricomycetes. Around 98% of the species are in the class Agaricomycetes, including all the agarics, bracket fungi, clavarioid fungi, corticioid fungi, and gasteroid fungi. Tremellomycetes contains many basidiomycete yeasts and some conspicuous jelly fungi. Dacrymycetes contains a further group of jelly fungi. These taxa are founded on molecular research, based on cladistic analysis of DNA sequences, and supersede earlier morphology-based classifications. Agaricomycotina contains nearly one third of all described species of fungi.

A ballistospore or ballistoconidia is a spore that is discharged into the air from a living being, usually a species of fungus. With fungi, most types of basidiospores formed on basidia are discharged into the air from the tips of sterigmata. At least 30 thousand species of mushrooms, basidiomycete yeasts, and other fungal groups may discharge ballistospores, sometimes at initial accelerations exceeding 10 thousand times g.

<i>Cyathus striatus</i> Species of fungus

Cyathus striatus, commonly known as the fluted bird's nest, is a common saprobic bird's nest fungus with a widespread distribution throughout temperate regions of the world. This fungus resembles a miniature bird's nest with numerous tiny "eggs"; the eggs, or peridioles, are actually lens-shaped bodies that contain spores. C. striatus can be distinguished from most other bird's nest fungi by its hairy exterior and grooved inner walls. Although most frequently found growing on dead wood in open forests, it also grows on wood chip mulch in urban areas. The fruiting bodies are encountered from summer until early winter. The color and size of this species can vary somewhat, but they are typically less than a centimeter wide and tall, and grey or brown in color. Another common name given to C. striatus, splash cups, alludes to the method of spore dispersal: the sides of the cup are angled such that falling drops of water can dislodge the peridioles and eject them from the cup. The specific epithet is derived from the Latin stria, meaning "with fine ridges or grooves".

<span class="mw-page-title-main">Hydnaceae</span> Family of fungi

The Hydnaceae are a family of fungi in the order Cantharellales. Originally the family encompassed all species of fungi that produced basidiocarps having a hymenium consisting of slender, downward-hanging tapering extensions referred to as "spines" or "teeth", whether they were related or not. This artificial but often useful grouping is now more generally called the hydnoid or tooth fungi. In the strict, modern sense, the Hydnaceae are limited to the genus Hydnum and related genera, with basidiocarps having a toothed or poroid hymenium. Species in the family are ectomycorrhizal, forming a mutually beneficial relationship with the roots of trees and other plants. Hydnum repandum is an edible species, commercially collected in some countries and often marketed under the French name pied de mouton.

<i>Crucibulum</i> (fungus) Genus of fungi

Crucibulum is a genus in the Nidulariaceae, a family of fungi whose fruiting bodies resemble tiny egg-filled bird's nests. Often called "splash cups", the fruiting bodies are adapted for spore dispersal by using the kinetic energy of falling drops of rain. The "eggs" inside the bird's nests are hard waxy shells containing spores, and tend to stick to whatever nearby herbage they land on, thus increasing the odds of being consumed and dispersed by herbivorous animals. Members of this genus are saprobic, obtaining nutrients from dead organic matter, and are typically found growing on decayed wood and wood debris. The three known Crucibulum species are distinguished from other genera of the Nidulariaceae by their relatively simple funiculus – a cord of hyphae that connects the peridiole to the exterior of the bird's nest.

<i>Nidula</i> Genus of fungi

Nidula is a genus of fungi in the family Agaricaceae. Their fruit bodies resemble tiny egg-filled birds' nests, from which they derive their common name "bird's nest fungi". Originally described in 1902, the genus differs from the related genera Cyathus and Crucibulum by the absence of a cord that attaches the eggs to the inside of the fruit body. The life cycle of this genus allows it to reproduce both sexually, with meiosis, and asexually via spores. Species in this genus produce a number of bioactive compounds, including 4-(p-hydroxyphenyl)-2-butanone, a major component of raspberry flavor and insect attractor used in pesticides.

<i>Cyathus olla</i> Species of fungus

Cyathus olla also known as the field bird's nest is a species of saprobic fungus in the genus Cyathus of the family Nidulariaceae. The fruit bodies resemble tiny bird's nests filled with "eggs" – spore-containing structures called peridioles. Like other bird's nest fungi, C. olla relies on the force of falling water to dislodge peridioles from fruiting bodies to eject and disperse their spores. The life cycle of this fungus allows it to reproduce both sexually, with meiosis, and asexually via spores. C. olla is a relatively common fungus, with a worldwide distribution. It is the subject of agricultural research to determine its potential as a means to accelerate the breakdown of crop residue, and reduce the population of plant pathogens. The specific epithet is derived from the Latin word olla, meaning "pot".

<i>Cyathus stercoreus</i> Species of fungus

Cyathus stercoreus, commonly known as the dung-loving bird's nest or the dung bird's nest, is a species of fungus in the genus Cyathus, family Nidulariaceae. Like other species in the Nidulariaceae, the fruiting bodies of C. stercoreus resemble tiny bird's nests filled with eggs. The fruiting bodies are referred to as splash cups, because they are developed to use the force of falling drops of water to dislodge and disperse their spores. The species has a worldwide distribution, and prefers growing on dung, or soil containing dung; the specific epithet is derived from the Latin word stercorarius, meaning "of dung".

Limnoperdon is a fungal genus in the monotypic family Limnoperdaceae. The genus is also monotypic, as it contains a single species, the aquatic fungus Limnoperdon incarnatum. The species, described as new to science in 1976, produces fruit bodies that lack specialized structures such as a stem, cap and gills common in mushrooms. Rather, the fruit bodies—described as aquatic or floating puffballs—are small balls of loosely interwoven hyphae. The balls float on the surface of the water above submerged twigs. Experimental observations on the development of the fruit body, based on the growth on the fungus in pure culture, suggest that a thin strand of mycelium tethers the ball above water while it matures. Fruit bodies start out as a tuft of hyphae, then become cup-shaped, and eventually enclose around a single chamber that contains reddish spores. Initially discovered in a marsh in the state of Washington, the fungus has since been collected in Japan, South Africa, and Canada.

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Ceratobasidium is a genus of fungi in the order Cantharellales. Basidiocarps are effused and the genus is sometimes grouped among the corticioid fungi, though species also retain features of the heterobasidiomycetes. Anamorphic forms were formerly referred to the genus Ceratorhiza, but this is now considered a synonym of Rhizoctonia. Ceratobasidium species, excluding the type, are also now considered synonymous with Rhizoctonia and some species have been transferred to the latter genus. Species are saprotrophic, but several are also facultative plant pathogens, causing a number of commercially important crop diseases. Some are also endomycorrhizal associates of orchids.

<span class="mw-page-title-main">Nidulariaceae</span> Family of fungi

The Nidulariaceae are a family of fungi in the order Agaricales. Commonly known as the bird's nest fungi, their fruiting bodies resemble tiny egg-filled birds' nests. As they are saprobic, feeding on decomposing organic matter, they are often seen growing on decaying wood and in soils enriched with wood chips or bark mulch; they have a widespread distribution in most ecological regions. The five genera within the family, namely, Crucibulum, Cyathus, Mycocalia, Nidula, and Nidularia, are distinguished from each other by differences in morphology and peridiole structure; more recently, phylogenetic analysis and comparison of DNA sequences is guiding new decisions in the taxonomic organization of this family.

<i>Marasmius funalis</i> Species of fungus

Marasmius funalis is a species of Marasmiaceae fungus known only from Japan. The species produces small mushrooms with reddish-brown caps up to 6 millimetres (0.24 in) in diameter and dark-brown, threadlike stems of up to 50 millimetres (2.0 in) in length. The species has a number of distinctive microscopic features, including very long cystidia on the stem, visible as bristles. Described in 2002 by Haruki Takahashi, the species grows on dead wood. The closest relative of M. funalis is M. liquidambari, known from Mexico and Papua New Guinea, and it is also similar in appearance to M. hudonii and Setulipes funaliformis, the latter of which was named after M. funalis.

<i>Mycena chlorophos</i> Species of agaric fungus in the family Mycenaceae

Mycena chlorophos is a species of agaric fungus in the family Mycenaceae. First described in 1860, the fungus is found in subtropical Asia, including India, Japan, Taiwan, Polynesia, Indonesia, and Sri Lanka, in Australia, and Brazil. Fruit bodies (mushrooms) have pale brownish-grey sticky caps up to 30 mm (1.2 in) in diameter atop stems 6–30 mm (0.2–1.2 in) long and up to a millimeter thick. The mushrooms are bioluminescent and emit a pale green light. Fruiting occurs in forests on fallen woody debris such as dead twigs, branches, and logs. The fungus can be made to grow and fruit in laboratory conditions, and the growth conditions affecting bioluminescence have been investigated.

<i>Sporobolomyces salmonicolor</i> Species of fungus

Sporobolomyces salmonicolor is a species of fungus in the subdivision Pucciniomycotina. It occurs in both a yeast state and a hyphal state, the latter formerly known as Sporidiobolus salmonicolor. It is generally considered a Biosafety Risk Group 1 fungus; however isolates of S. salmonicolor have been recovered from cerebrospinal fluid, infected skin, a nasal polyp, lymphadenitis and a case of endophthalmitis. It has also been reported in AIDS-related infections. The fungus exists predominantly in the anamorphic (asexual) state as a unicellular, haploid yeast yet this species can sometimes produce a teleomorphic (sexual) state when conjugation of compatible yeast cells occurs. The asexual form consists of a characteristic, pink, ballistosporic yeast. Ballistoconidia are borne from slender extensions of the cell known as sterigmata and are forcibly ejected into the air upon maturity. Levels of airborne yeast cells peak during the night and are abundant in areas of decaying leaves and grains. Three varieties of Sporobolomyces salmonicolor have been described; S. salmonicolor var. albus, S. salmonicolor var. fischerii, and S. salmonicolor var. salmoneus.

Chionosphaera is a genus of fungi in the family Chionosphaeraceae. It has four species.

References

  1. Donk, M.A. (1963). "A conspectus of the families of Aphyllophorales". Persoonia. 3 (3): 214.
  2. Money, N.P. (1998). "More g's than the Space Shuttle: Ballistospore discharge". Mycologia. 90 (4): 547–558. doi:10.1080/00275514.1998.12026942.