Panellus stipticus

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Panellus stipticus
A cluster of about a dozen light brown, roughly fan-shaped mushroom caps growing from a piece of rotting wood. Also visible on the wood are a few scattered smaller caps, and patches of green lichen.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Basidiomycota
Class: Agaricomycetes
Order: Agaricales
Family: Mycenaceae
Genus: Panellus
Species:
P. stipticus
Binomial name
Panellus stipticus
(Bull.) P.Karst. (1879)
Synonyms
  • Agaricus stypticus Bull. (1783)
  • Merulius stipticus (Bull.) Lam. (1815)
  • Crepidopus stypticus (Bull.) Gray (1821)
  • Rhipidium stipticum (Bull.) Wallr. (1833)
  • Panus stipticus (Bull.) Fr. (1838)
  • Pleurotus stipticus (Bull.) P.Kumm. (1871)
  • Lentinus stipticus (Bull.) J.Schröt. (1889)
  • Pocillaria stiptica (Bull.) Kuntze (1898)
Panellus stipticus
View the Mycomorphbox template that generates the following list
Gills on hymenium
Cap is convex or offset
saprotrophic
Edibility is inedible

Panellus stipticus, commonly known as the bitter oyster, the astringent panus, the luminescent panellus, or the stiptic fungus, is a species of

Molecular phylogenetic analysis revealed P. stipticus to have a close genetic relationship with members of the genus Mycena
.

Panellus stipticus is one of several dozen species of fungi that are

mycelia grown in laboratory culture, and the growth conditions for optimal light production have been studied in detail. Several chemicals have been isolated and characterized that are believed to be responsible for light production. Genetic analysis has shown that luminescence is controlled by a single dominant allele. The luminescent glow of this and other fungi inspired the term foxfire, coined by early settlers in eastern and southern North America. Modern research has probed the potential of P. stipticus as a tool in bioremediation, because of its ability to detoxify various environmental pollutants
.

Taxonomy and phylogeny

Phylogeny and relationships of P. stipticus and related species based on ribosomal DNA sequences[1]

The species was first named Agaricus stypticus by the French botanist

Petter Karsten who in 1879 assigned its current name.[12] Panellus stypticus is still used in the literature as a variant spelling.[13]

Panellus stipticus is the

Orson K. Miller, who in 1975 suggested merging Dictyopanus into Panellus based on similarities in spore shape, stem structure, and the ability of dried fruit bodies to revive when moistened.[15] Formerly grouped in the family Tricholomataceae,[16] a wastebasket taxon of gilled mushrooms with white spores, P. stipticus is now classified in the Mycenaceae,[17][18] after a large-scale phylogenetic analysis revealed "a previously unsuspected relationship between Mycena and Panellus (including Dictyopanus)".[19]

The fungus is

specific epithet stipticus refers to its purported value in stopping bleeding.[24][25] Etymologically, it is a Greek equivalent to the Latin word astringens, deriving from στυπτικός (styptikós), itself from the verb στύφειν (styphein), "to contract".[26][27]

Description

The undersides of a cluster of about two dozen variously sized light brown-yellow, roughly fan-shaped mushroom caps growing on a piece of rotting wood. Each cap has about 2–3 dozen lightly colored thin lines of various lengths, closely spaced and arranged radially around the stem, which is connected to one side of the mushroom cap. The stem is whitish, with a width of between roughly one-third to one-fifth the diameter of the cap, and attaches the cap to the wood.
The buff-colored gills are closely spaced together, and are connected by cross-veins.

The fungus normally exists unseen, in the form of a mass of threadlike

buff to cinnamon; when dried they may be various shades of tan, brown or clay. The faded colors of dried fruit bodies tend to revive when moistened. On the underside of the cap, the gills are narrow and spaced closely together, often forked, buff-colored, and with numerous interconnecting cross-veins. Holding the cap in position is a stem that is 0.6 to 1.2 cm (0.2 to 0.5 in) long by 0.3 to 0.8 cm (0.1 to 0.3 in) thick, and has an off-center attachment to the cap, either at or near the cap side. The dull-white stem is covered with minute silk-like fibers, and is narrower at the base where it attaches to the substrate. Fruit bodies do not have any distinctive odor.[15] The flesh is thin and tough, and dark yellow-brown to cream-colored.[29]

Microscopic features

Various microscopic characteristics may be used to help identify the fungus from other morphologically similar species. A spore print of P. stipticus, made by depositing a large number of spores in a small area, reveals their color to be white.[21] Viewed with a microscope, the spores are smooth-walled, elliptical to nearly allantoid (sausage-shaped), with dimensions of 3–6 by 2–3 µm. Spores are amyloid, meaning that they will absorb iodine and become bluish-black when stained with Melzer's reagent,[30] but this staining reaction has been described as "relatively weak".[1]

The

cheilocystidia are found on the gill edge; in P. stipticus they are narrowly club-shaped, cylindrical, spindle-shaped to bifurcate at the apex. They are also thin-walled, hyaline (translucent), abundant and crowded, and measure 17–45 by 3.5–6 µm. The pleurocystidia, located on the gill face, are 17–40 by 3–4.5 µm, spindle- or club-shaped, sometimes bifurcate at the apex, thin-walled, and hyaline. They are scattered or in dense clusters, mostly embedded in hymenium, occasionally protruding up to half the width of the hymenium.[15]

The flesh of the cap consists of a number of microscopically distinct layers of tissue. The cuticle of the cap (known as the pileipellis) is between 8–10 µm thick,[32] and is made of a loose textura intricata, a type of tissue in which the hyphae are irregularly interwoven with distinct spaces between them.[15] The cuticle hyphae are thick-walled to thin-walled, with scattered inconspicuous cystidia measuring 40–55 by 3.5–5.5 µm. These cystidia located in the cap (pileocystidia) are cylindrical, thin-walled, yellow in Melzer's reagent, hyaline in KOH, sometimes with amorphous dingy brown material coating the walls. Beneath the cuticle layer is a zone 54–65 µm thick, made of very loosely entwined, thin-walled hyphae, 2–3 µm in thickness, with clamps at the septa. Below this is a zone 208–221 µm in thickness, in which the densely compacted hyphae, 3–8 µm in diameter, have swollen, gelatinized walls, and often more or less a vertical orientation. This in turn is followed by a layer 520 µm in thickness, formed of loosely interwoven hyphae, 2–8 µm in width, some of which have thin walls with clamps at the septa, whilst others have somewhat thickened gelatinized walls.[32] The flesh of the cap has a layer of upright hyphae bending into a lower layer of interwoven hyphae with diameters of 2.5–8 µm. The flesh of the gills is similar to that of the lower cap.[15]

Similar species

The underside of a single whitish to light brown, fan-shaped mushroom cap growing on a piece of wood. The cap has about 3 dozen lightly colored thin sections of tissue, closely spaced and arranged radially from a point originating near the surface of the wood.
The underside of a fan-shaped mushroom cap growing on a piece of wood. The cap is light gray, has about 3 dozen lightly colored thin sections of tissue, closely spaced and arranged radially from a point originating near the surface of the wood. Four other similarly shaped smaller caps are beside or overlapping the larger cap.
Possible lookalike species include Crepidotus mollis (top) and Schizophyllum commune (bottom).

Species of Crepidotus having a similar shape can be distinguished by their brown spore print, compared with the white spore print of P. stipticus.[20] Schizophyllum commune has a densely hairy white to grayish cap and longitudinally split gill-folds on the underside.[25] The ruddy panus mushroom (Panus rudis) is larger, has a reddish-brown cap that fades to pinkish-tan, and shows lilac tinges when young, fresh, and moist.[23] Some Paxillus species may have a similar appearance, but they have yellow-brown spore prints.

Uses

Panellus stipticus is considered too small and bitter to be

styptic to staunch bleeding,[35] and also as a "violent purgative".[23]

Fruit body development

Fruit bodies first appear as tiny white knobs less than a cubic millimeter in size. In a day or two the knobs grow into a horizontal pyramidal mass, increasing in height as the hyphae lengthen. This is soon followed by the formation of a minute cap, and lengthening of the stem. The stem is about 1 mm long when the cap first begins to form. The hyphae that comprise the stem gradually cease to grow at their ends, and then start to branch, with many of the branches growing in a horizontal direction. This growth, indicated by the flattening and broadening out of the top of the stem, gives rise to the cap. The horizontally aligned hyphae grow vertical branches which remain more or less parallel, ultimately forming the dorsal tissue of the cap. Other similar downward-growing branches form the fertile hymenium, which can be seen when the cap is about 2 mm in diameter.[36]

A group of about a half dozen overlapping light brownish-yellow mushroom caps clustered together on piece of rotting wood. Above the parger caps are several small mushrooms, the same color as the larger caps, but with round heads attached to relatively thick stems that in length are about one to three times the width of the cap.
The caps of young fruit bodies (top) are spherical, and grow epinastically, so that the developing gills remain enclosed until maturity.

The young cap is spherical and its growth is at first epinastic, its margin being curved inwards and pressed against the stem. In this way, the hymenium begins its development within a special enclosed chamber. As the hymenial surface increases and keeps pace with the growth of the dorsal tissue of the cap, the latter expands and exposes the gills. The gills are formed by the continual downward growth of some of the hyphae. The gills are exposed before the cap is completely developed, and before the spores are mature. Spores can be produced by fruit bodies as small as 1.3 cm (0.5 in) broad, and liberation of the spores continues until the fruit body is fully grown—a period of one month to three months, depending on the conditions of temperature and moisture. The mature spores are disseminated by the wind. When the fruit body is nearing maturity, some of the terminal portions of the hyphae of the dorsal surface of the cap separate, and as a consequence, the upper surface of the fruit body becomes granular in appearance.[36]

The fruit body projects out horizontally from the growing surface. If the position of a log is altered after young fruit bodies with the beginnings of gills have appeared, the stems of these attempt to readjust themselves in order to place the cap in a horizontal position. The cap are sometimes zonate (marked with concentric lines that form alternating pale and darker zones); this depends on changes in the humidity of the environment, as variations in the amount of moisture will cause alternating periods of acceleration or slowing of growth.[36]

A yellowish-brown pigment is diffused through the

buff, but soon the color of the cap deepens and becomes cinnamon. The intensity of the color appears to be dependent on light, for when fruit bodies are grown in diffuse light (temperature and humidity being constant) they are a uniform pale buff color, but in bright light they are cinnamon or tan.[36]

Distribution, habitat, and ecology

A long clustered row showing the undersides of an orangeish-brown fan-shaped fungus.
Fruit bodies can grow in dense overlapping clusters.

Panellus stipticus is common in northern

temperate regions of Europe, and has also been collected in Australia,[37] New Zealand,[38] Anatolia,[39] Japan,[34] and China.[31] In North America, it is more common in the east than the west;[13][23] the mushroom's northern range extends to Alaska, and it has been collected as far south as Costa Rica.[40]

Panellus stipticus is a

eastern white pine.[44] Fruiting occurs September through November in Europe, the Canary Islands,[46] and North America,[15] although it may also sometimes be found in the spring.[20] The fruit bodies are long-lasting and may be found year-round.[47] It is an "early-stage" succession fungus, not typically recorded from plantations over 20 years old.[48]

The fruit bodies are frequently attacked by slugs, which may be important agents in the dispersal of its spores.[23] White-tailed deer are also known to consume the fungus.[49]

Mating studies

Panellus stipticus uses a

heterothallic, tetrapolar mating system:[43][50] each basidiospore develops into a self-sterile mycelium which, when grown alone, remains homokaryotic (i.e., with all cells genetically identical) indefinitely. Researchers have paired collections of P. stipticus from Japan and Eastern North America, and later, collections from New Zealand and Russia.[34][51] Although the separated allopatric populations differ in bioluminescence and taste, the results revealed a universal intercompatibility group over these geographical regions.[52] In a 2001 study, Jin and colleagues also paired geographically representative collections of the fungus, but observed a reduced ability to cross between Northern Hemisphere and Oceanian collections, as well as between and within Oceanian collections.[40]

Bioluminescence

A cluster of bright green glowing mushroom caps growing on a log. The remainder of the photo is dark, but suggests there are trees around.
Bioluminescence demonstrated: the camera was exposed for 517 seconds to capture this much light.

oxidizing a pigment called a luciferin. In some areas, P. stypticus is bioluminescent, and the fruit bodies of these strains will glow in the dark when fresh or sometimes when revived in water after drying.[25]

An early record of luminescence noted in P. stypticus was made by the American naturalist

Journal of Mycology
, wrote:

By careful examination, the luminosity was found to proceed from the gills and not the stipe, nor from any fragment of rotten wood attached to the specimen. This phosphorescence was not observed in all specimens brought in for examination, and seemed to depend on some peculiar condition of the air, having been noticed only in specimens gathered in damp weather or just before a storm.[56]

Canadian mycologist Buller in 1924 described the gills of P. stipticus in North America as luminescent, and noted that the fungus glows most strongly at the time of spore maturation.[42] Bioluminescence has not been observed in European specimens,[43] in Pacific North American collections, nor in strains collected from New Zealand, Russia, and Japan.[34] Although a number of reports have confirmed that eastern North American strains are luminescent,[34][44][51][57][58] non-luminescent North American strains are also known.[54] In general, the intensity of fungal bioluminescence decreases after exposure to certain contaminants; this sensitivity is being investigated as a means to develop bioluminescence-based biosensors to test the toxicity of polluted soils.[59] Most known luminescent fungi are in the genus Mycena or closely allied genera; this grouping of fungi—known as the "mycenoid lineage"—includes P. stipticus and three other Panellus species.[60]

Mycelia

The

mycelia of this species, grown in laboratory culture, have also been shown to be bioluminescent.[61] Early studies demonstrated that short-wave ultraviolet light (at a wavelength of 280 nm) reversibly inhibited the luminescence of P. stypticus mycelia, while longer wavelength (366 nm) ultraviolet was stimulatory.[62][63] Further, the fungus exhibited a pronounced diurnal periodicity, and maximum luminescence was noted between 6 and 9 pm, regardless as to whether the mycelial cultures were incubated in continuous light, continuous darkness, or a normal day-night cycle.[64] The mycelia of P. stipticus grown submerged in liquid were non-luminescent, but became luminescent while growing on solid substrata. Dark-grown colonies were luminescent in the center, and light-grown colonies were brightest at the periphery.[61] Other experiments have shown that growth temperature and pH have a significant effect on the level of bioluminescence, optimized at 22 °C (72 °F) and pH 3–3.5. However, light had a significant effect on mycelial growth but not on bioluminescence, and the optimal light conditions for maximum bioluminescence were total darkness.[65]

Fruit bodies

Bioluminescent tissue in the mature fruit body is restricted to the edge of the gills (as well as the cross-veins that connect them), the junction of the gills with the stem, and the inrolled cap edge. Distribution of bioluminescence along the gill edge corresponds to the position of the cheilocystidia. Less than 10% of the light emitted from both the young and mature fruit bodies is from other tissues, including the fertile hymenial area and the stem. Fruit body luminescence is highly variable between fruit bodies found on different logs in different environments.[58]

Genetics

A sequence of three pictures showing the effect of shining a light on a cluster of fan-shaped mushrooms growing on a log. When the lights hits the mushroom cluster, it glows green; when the light is moved away, the glow disappears.
In Mount Vernon, Wisconsin

Using techniques of genetic complementation, Macrae paired nonluminescent monocaryons with luminescent ones, and concluded that luminosity in P. stipticus is an inherited character, and governed by a single pair of alleles in which luminosity was dominant over nonluminosity. Luminosity factors were independent of intersterility factors. In 1992, Lingle and colleagues agreed with Macrae about luminosity and stated that at least three different gene mutations could lead to the loss of luminescence. They also reported that the maximum bioluminescence was found at 525 nm, and shifted to 528 nm in deeply pigmented fruit bodies.[44]

After intercontinental compatibility tests, Petersen and Bermudes suggested that bioluminescence and compatibility were independent since bioluminescence seemed to be geographically restricted. This suggested that the ability or potential to interbreed must have been preserved since separation of P. stypticus into geographically isolated areas.[34][51]

Function

Several authors have suggested that the purpose of fungal bioluminescence is to attract

Basidiomycete mushrooms are known to be dependent on an adequate moisture supply for proper development.[69] In species with a luminous mycelium, the mycelium would therefore have a dual function in performing the fungal translocation that permits transport of substances from the further environment back to the fruiting body, and in attracting disseminating vectors towards environments favorable for development of the species.[55]

Chemical basis

C15H18O5
The chemical structure of panal

In general, bioluminescence is caused by the action of

iron(II), hydrogen peroxide, and a cationic surfactant, light is emitted by a chemiluminescence reaction,[71][72] suggesting that panal and its derivatives are fungal luciferins, and that the chemiluminescence reaction is the cause of in vivo bioluminescence.[73][74] In the fungus, the level of activity of the enzyme superoxide dismutase (SOD) appears to play a critical role in the amount of light emission. SOD quenches the effect of the superoxide (O2−) anion required in the reaction, and thus SOD activity has to be inhibited for the reaction to occur.[54]

Bioremediation

As a white-rot fungus, Panellus stipticus contains enzymes that are able to break down

mycelia reduced the initial concentration of phenolic compounds by 42% after a 31-day incubation period.[75] In a separate study, a P. stipticus culture was able to effectively degrade the environmental pollutant 2,7-dichlorodibenzo-p-dioxin, a polychlorinated dioxin.[76]

See also

References

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