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Myco-heterotrophy (from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
μύκης , "fungus", ἕτερος ', "another", "different" and τροφή ', "nutrition") is a
symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...
relationship between certain kinds of
plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
and
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
, in which the plant gets all or part of its food from
parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
upon fungi rather than from
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. A myco-heterotroph is the
parasitic plant A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. They make up about 1% of angiosperms and are found in almost every biome. All parasitic plants develop a specialized organ called th ...
partner in this relationship. Myco-heterotrophy is considered a kind of
cheating Cheating generally describes various actions designed to subvert rules in order to obtain unfair advantages. This includes acts of bribery, cronyism and nepotism in any situation where individuals are given preference using inappropriate crit ...
relationship and myco-heterotrophs are sometimes informally referred to as "mycorrhizal cheaters". This relationship is sometimes referred to as mycotrophy, though this term is also used for plants that engage in mutualistic
mycorrhizal   A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the pl ...
relationships.


Relationship between myco-heterotrophs and host fungi

Full (or obligate) myco-heterotrophy exists when a non-photosynthetic plant (a plant largely lacking in
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
or otherwise lacking a functional
photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosy ...
) gets all of its food from the fungi that it parasitizes. Partial (or facultative) myco-heterotrophy exists when a plant is capable of photosynthesis, but parasitizes fungi as a supplementary food supply. There are also plants, such as some
orchid Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of floweri ...
species, that are non-photosynthetic and obligately myco-heterotrophic for part of their life cycle, and photosynthetic and facultatively myco-heterotrophic or non-myco-heterotrophic for the rest of their life cycle. Not all non-photosynthetic or " achlorophyllous" plants are myco-heterotrophic – some non-photosynthetic plants like
dodder ''Cuscuta'' (), commonly known as dodder or amarbel, is a genus of over 201 species of yellow, orange, or red (rarely green) parasitic plants. Formerly treated as the only genus in the family Cuscutaceae, it now is accepted as belonging in the ...
directly parasitize the
vascular tissue Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. The ...
of other plants. The partial or full loss of photosynthesis is reflected by extreme physical and functional reductions of plastid genomes in mycoheterophic plants, an ongoing evolutionary process. In the past, non-photosynthetic plants were mistakenly thought to get food by breaking down
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
in a manner similar to
saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...
fungi. Such plants were therefore called " saprophytes". It is now known that these plants are not physiologically capable of directly breaking down organic matter and that in order to get food, non-photosynthetic plants must engage in parasitism, either through myco-heterotrophy or direct parasitism of other plants. The interface between the plant and fungal partners in this association is between the roots of the plant and the mycelium of the fungus. Myco-heterotrophy therefore closely resembles
mycorrhiza   A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plan ...
(and indeed is thought to have evolved from mycorrhiza), except that in myco-heterotrophy, the flow of carbon is from the fungus to the plant, rather than vice versa. Most myco-heterotrophs can therefore be seen as ultimately being epiparasites, since they take energy from fungi that in turn get their energy from
vascular plants Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
. Indeed, much myco-heterotrophy takes place in the context of common
mycorrhizal network A Mycorrhizal network (also known as a common mycorrhizal network or CMN) is an underground network found in forests and other plant communities, created by the hyphae of mycorrhizal fungi joining with plant roots. This network connects individu ...
s, in which plants use mycorrhizal fungi to exchange carbon and nutrients with other plants. In these systems, myco-heterotrophs play the role of "mycorrhizal cheaters", taking carbon from the common network, with no known reward. A special form of mycoheterotrophic association, which appears to be a chimera between the haustorial parasitism of a
parasitic plant A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. They make up about 1% of angiosperms and are found in almost every biome. All parasitic plants develop a specialized organ called th ...
and mycoheterotrophy, is observed in '' Parasitaxus usta'', the only mycoheterotrophic gymnosperm. In congruence with older reports, it has been recently shown that some myco-heterotrophic orchids can be supported by saprotrophic fungi, exploiting litter- or wood-decaying fungi. In addition, several green plants (evolutionarily close to myco-heterotrophic species) have been shown to engage in partial myco-heterotrophy, that is, they are able to take carbon from mycorrhizal fungi, in addition to their photosynthetic intake.


Species diversity of myco-heterotrophs and host fungi

Myco-heterotrophs are found among a number of plant groups. All monotropes and non-photosynthetic
orchids Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of flowering ...
are full myco-heterotrophs, as is the non-photosynthetic
liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...
'' Cryptothallus''. Partial myco-heterotrophy is common in the Gentian family, with a few genera such as ''
Voyria ''Voyria'', commonly known as ghostplants, is a genus of 20 species of herbaceous perennial plants, belonging to the family Gentianaceae. They are mostly native to warm temperate and tropical regions of the Caribbean, Central America and South ...
'' being fully myco-heterotrophic; in photosynthetic orchids; and in a number of other plant groups. Some
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...
s and
clubmosses Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching ...
have myco-heterotrophic
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...
stages.Taylor DL, Bruns TD, Leake JR, Read DJ. 2002
Mycorrhizal specificity and function in myco-heterotrophic plants.
In: ''Mycorrhizal Ecology'' (Sanders IR, van der Heijden M, eds.), Ecological Studies vol. 157, pp 375–414. Berlin: Springer-Verlag. . (NOTE: this PDF is from the page proofs, and is not identical to the published version)
The fungi that are parasitized by myco-heterotrophs are typically fungi with large energy reserves to draw on, usually mycorrhizal fungi, though there is some evidence that they may also parasitize parasitic fungi that form extensive mycelial networks, such as ''
Armillaria ''Armillaria'' is a genus of fungi that includes the ''Armillaria mellea, A. mellea'' species known as honey fungi that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armill ...
''. Examples of fungi parasitized by myco-heterotrophic plants can be found among the
ectomycorrhizal An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or my ...
, arbuscular mycorrhizal, and orchid mycorrhizal fungi. The great diversity in unrelated plant families with myco-heterotrophic members, as well as the diversity of fungi targeted by myco-heterotrophs, suggests multiple parallel evolutions of myco-heterotrophs from mycorrhizal ancestors.


References


Further reading

* * * Werner PG. 2006
Myco-heterotrophs: hacking the mycorrhizal network.
''
Mycena News The Mycological Society of San Francisco (MSSF) is an amateur club based in the San Francisco Bay Area, "dedicated to promoting the understanding and enjoyment of fungi." Meetings are held every third Tuesday, and the society newsletter, ''Myc ...
'' 57(3): 1,8.
Dr. Martin Bidartondo: Selected publications





External links



''The Parasitic Plant Connection'', SIU Carbondale, College of Science.
''Wayne's Word'' Noteworthy Plant For June 1997: Fungus Flowers – Flowering Plants that Resemble Fungi
by WP Armstrong.

by Tom Volk, ''TomVolkFungi.net''

– images of myco-heterotrophs by mycologist Martín Bidartondo. {{DEFAULTSORT:Myco-Heterotrophy Botany Ecology Mycology * Parasites of fungi Symbiosis