fungal filament motility

Date:   6/27/2013 9:06:40 AM ( 11 y ago)

The growth of fungi as hyphaeon or in solid substrates or as single cells in aquaticenvironments is adapted for the efficient extraction of nutrients, because thesegrowth forms have high surfacearea to volume ratios.[52] Hyphaeare specifically adaptedfor growth on solid surfaces, and to invade
substratesand tissues. [53] They can exert large penetrative mechanical forces; for example, the plant pathogenMagnaporthe grisea forms a structure called an
appressorium that evolved to puncture plant tissues. [54] The pressure generatedby the appressorium, directed againstthe plantepidermis , can exceed 8
megapascals(1,200 psi). [54] The filamentous fungus Paecilomyces lilacinus usesa similar structure to penetrate theeggs of
nematodes .[55]
The mechanical pressureexerted by the appressorium is generated from physiological processes that increaseintracellular turgor by producingosmolytessuchas
glycerol.[56] Morphological adaptationssuch astheseare complementedby hydrolytic enzymessecreted into the environment to digest large organic molecules—such as
polysaccharides , proteins, lipids, and other organic substrates—into smaller molecules that may then be absorbedas nutrients.[57][58]
[59] Thevast majority of filamentous fungi grow in a polar fashion—i.e., by extension into one direction—by elongation at the tip (apex) of the hypha.[60] Alternative forms of fungal growth include intercalary extension (i.e., by longitudinal expansion of hyphal compartments that are below the apex) as in the case of some
endophyticfungi,[61] or growth by volume expansion during the development of mushroom stipes and other large organs. [62] Growth of fungi as multicellular structuresconsisting of somatic and reproductive cells—a feature independently evolved in animals and plants[63]—has several functions, including the development of fruiting bodies for dissemination of sexualspores (seeabove) and biofilms for substratecolonization and
intercellular communication .[64]
The fungi are traditionally consideredheterotrophs, organisms that rely solely on
carbon fixed by other organisms for metabolism. Fungi have
evolved a high degree of metabolic versatility that allows them to use a diverserangeof organic substratesfor growth, including simple compounds such as nitrate, ammonia, acetate , or
ethanol .[65][66] For some species it has beenshownthat the pigment melanin may play a role in extracting energy from ionizing radiation, such as gamma radiation; however, this form of
"radiotrophic" growth has been described for only a few species, the effects on growth rates are small, and the underlying
biophysicaland biochemical processes arenot known.[31] The authors speculatethat this process might bear similarity to CO2 fixation via visible light, but insteadutilizing ionizing radiation as a sourceof energy.[67]

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