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==Reproduction and dispersal==
==Reproduction and dispersal==


A large number of lichens disperse very effectively by means of symbiotic vegetative propagules such as soredia, isidia and blastidia, and thallus fragmentation. However, ''X. parietina'' does not produce the vegetative propagules, but has to establish the symbiotic state at each reproductive cycle. It has been demonstrated that two orbatid mite species, ''[[Trhypochtonius tectorum]]'', and ''[[Trichoribates trimaculatus]]'', common inhabitant and consumers of ''X. parietina'', are vectors of the photobiont cells. Faecal pellets of both species contain both viable ascospores and photobiont cells, and are suggested to be a common mode of vegettive short- and long-distance dispersal of this species.<ref>Meier FA, Scherrer S, Honegger R. (2002). "Faecal pellets of lichenivorous mites contain viable cells of the lichen-forming ascomycete ''Xanthoria parietina'' and its green algal photobiont, ''Trebouxia arbicola''." ''Biological Journal of the Linnean Society'''''76'''(2): 259&ndash;268.</ref>
A large number of lichens disperse very effectively by means of symbiotic vegetative propagules such as soredia, isidia and blastidia, and thallus fragmentation. However, ''X. parietina'' does not produce the vegetative propagules, but has to establish the symbiotic state at each reproductive cycle. It has been demonstrated that two orbatid mite species, ''[[Trhypochtonius tectorum]]'', and ''[[Trichoribates trimaculatus]]'', common inhabitant and consumers of ''X. parietina'', are vectors of the photobiont cells. Faecal pellets of both species contain both viable ascospores and photobiont cells, and are suggested to be a common mode of vegetative short- and long-distance dispersal of this species.<ref>Meier FA, Scherrer S, Honegger R. (2002). "Faecal pellets of lichenivorous mites contain viable cells of the lichen-forming ascomycete ''Xanthoria parietina'' and its green algal photobiont, ''Trebouxia arbicola''." ''Biological Journal of the Linnean Society'''''76'''(2): 259&ndash;268.</ref>


==Habitat and distribution==
==Habitat and distribution==

Revision as of 20:08, 6 September 2010

Xanthoria parietina
Scientific classification
Kingdom:
Fungi
Division:
Ascomycota
Class:
Lecanoromycetes
Order:
Teloschistales
Family:
Teloschistaceae
Genus:
Xanthoria
Species:
X. parietina
Binomial name
Xanthoria parietina
(L.) Th. Fr. (1860)

Xanthoria parietina is a foliose, or leafy, lichen. It has wide distribution, and many common names such as common orange lichen, yellow scale, maritime sunburst lichen and shore lichen. It can be found near the shore on rocks or walls (hence the epithet parietina meaning "on walls"), and also on inland rocks, walls, or tree bark. It was chosen as a model organism for genomic sequencing (planned in 2006) by the US Department of Energy Joint Genome Institute (JGI). In the past it was used as a remedy for jaundice because of its yellow color.

X. parietina growing on brick...
... and on a dead branch.

Taxonomy

The species was first described by Carl Linnaeus in 1753, as Lichen parietinus.

Description

The vegetative body of the lichen, the thallus, is foliose, and typically less than 8 centimetres (3.1 in) wide. The lobes of the thallus are 1–4 mm in diameter, and flattened down. The upper surface is some shade of yellow, orange, or greenish yellow, while the lower surface is white, with a cortex, and with sparse pale rhizines or hapters. The vegetative reproductive structures soredia and isidiaare absent in this species, however, apothecia are usually present.[1]

The outer "skin" of the lichen, the cortex, is composed of closely packed fungal hyphae and serves to protect the thallus from water loss due to evaporation as well as harmful effects of high levels of irradiation. In Xanthoria parietina, the thickness of the thalli is known to vary depending on the habitat is which it grows. Thalli are much thinner in shady locations than in those exposed to full sunshine; this has the effect of protecting the algae that cannot tolerate high light intensities. The lichen pigment parietin gives this species a deep yellow or orange-red color.[2]

X. parietina prefers growing on bark and wood; it is found more rarely on rock.[1] Nutrient enrichment by bird droppings enhances the ability of X. parietinato grow on rock.[3]

Photobiont

The photosynthetic symbionts, or photobionts, associated with X. parietina are from the green algal genus Trebouxia. Species that have been found include Trebouxia arboricola and T. irregularis.[4] Both of these photobionts are known to occur free-living in nature, having been found on bark colonized by X. parietina as well as on bark not colonized by lichens.[5]

In one study, the photobiont was shown to occupy 7% of the volume of the thallus.[6] The density of pigmentation of the upper cortex also varies and seems to control the amount of light reaching the algae.[6]

Reproduction and dispersal

A large number of lichens disperse very effectively by means of symbiotic vegetative propagules such as soredia, isidia and blastidia, and thallus fragmentation. However, X. parietina does not produce the vegetative propagules, but has to establish the symbiotic state at each reproductive cycle. It has been demonstrated that two orbatid mite species, Trhypochtonius tectorum, and Trichoribates trimaculatus, common inhabitant and consumers of X. parietina, are vectors of the photobiont cells. Faecal pellets of both species contain both viable ascospores and photobiont cells, and are suggested to be a common mode of vegetative short- and long-distance dispersal of this species.[7]

Habitat and distribution

Hardwood forests in low-elevation broad valleys; scattered on Populus and other hardwoods in riparian areas in agricultural and populated areas.[1] It is often associated with high level of nitrogen and favored by eutrophication [8][9] and can be often found near farmland and around livestock.[10]

X. parietina is a widespread lichen, and has been reported from Australia, Africa, Asia, North America[11] and throughout much of Europe.[12] In eastern North America and Europe, it is found more frequently near coastal locations.[1] The increases in NO3 deposition as a result of industrial and agricultural developments in southern Ontario, Canada in the 20th century are thought to be responsible for the reappearance of this species in the local lichen flora.[13]

Pollution tolerance

Xanthoria parietina is a very pollution-tolerant species. In laboratory experiments, this species can tolerate exposure to air contaminants and bisulphite ions with little or no damaging effect.[14] It is also tolerant of heavy metal contamination.[15]

For these reasons, this species has found use as a biomonitor for measuring levels of toxic elements.[16][17]

Bioactive compounds

Structure of parietin, orange-colored pigment found in X. parietina.

X. parietina produces an orange colored anthraquinone pigment, parietin, that gets deposited as tiny crystals in the top layer of the upper cortex. Parietin synthesis is enhanced by UV-B,[18] and stimulated by photosynthates, such as those provided by the green algal Trebouxia symbiont.[19] X. parietina also produces the metabolite 2-methoxy-4,5,7-trihydroxy-anthraquinone.[20]






Medicinal properties

The water extract of X. parietina has good antiviral activity in vitro, inhibiting the replication of human parainfluenza virus type 2.[21]

References

  1. ^ a b c d Geiser, Linda; McCune, Bruce (1997). Macrolichens of the Pacific Northwest. Corvallis: Oregon State University Press. p. 321. ISBN 0-87071-394-9.{{cite book}}: CS1 maint: multiple names: authors list (link) Cite error: The named reference "isbn0-87071-394-9" was defined multiple times with different content (see the help page).
  2. ^ Galun, Margalith (1988). CRC Handbook of Lichenology, Volume I. Boca Raton: CRC. p. 105. ISBN 0-8493-3581-7.
  3. ^ Armstrong RQ. (1984). "The influence of bird droppings and uric acid on the growth of five species of saxicolous lichens." Environmental and Experimental Botany 24: 95.
  4. ^ Ahmadjian, Vernon. (1993). The lichen symbiosis. New York: John Wiley. pp. 32–33. ISBN 0-471-57885-1.
  5. ^ Bubrick P, Galun M, Frensdorff A. (1984). "Observations on free-livingTrebouxia de Puymaly and Psuedotrebouxia Archibald, and evidence that both symbionts from Xanthoria parietina (L.) Th. Fr. can be found free-living in nature." New Phytologist 97: 455.
  6. ^ a b Biology of Lichens. Cambridge, UK: Cambridge University Press. 1983. p. 51. ISBN 0-7131-2457-1. Cite error: The named reference "isbn0-7131-2457-1" was defined multiple times with different content (see the help page).
  7. ^ Meier FA, Scherrer S, Honegger R. (2002). "Faecal pellets of lichenivorous mites contain viable cells of the lichen-forming ascomycete Xanthoria parietina and its green algal photobiont, Trebouxia arbicola." Biological Journal of the Linnean Society76(2): 259–268.
  8. ^ Gaio-Oliveira G, Dahlman L, Palmqvist K, Máguas C. (2004). "Ammonium uptake in the nitrophytic lichen Xanthoria parietina and its effects on vitality and balance between symbionts."Lichenologist 36: 75–86.
  9. ^ Van Herk CM. (1999). "Mapping of ammonia pollution with epiphytic lichens in The Netherlands." Lichenologist 31:9–20.
  10. ^ Frati L, Santoni S, Nicolardi V, Gaggi C, Brunialti G, Guttova A, Gaudino S, Pati A, Pirintsos SA, Loppi S. (2007). Lichen biomonitoring of ammonia emission and nitrogen deposition around a pig stockfarm. Environmental Pollution 146: 311&ndsash;6.
  11. ^ Hogan, C. Michael. 2008. Black Spruce: Picea mariana, GlobalTwitcher.com, ed. Nicklas Stromberg
  12. ^ Lindblom L. (1997). "The genus Xanthoria (Fr.) Th. Fr. in North America." Journal of the Hattori Botanical Laboratory 83:75–172.
  13. ^ Brodo IM, Lewis C, Craig B. (2007). "Xanthoria parietina, a coastal lichen, rediscovered in Ontario." Northeastern Naturalist 14(2): 300–6.
  14. ^ Silberstein L, Siegel BZ, Sigel SM, Mukhtar A, Galun M. (1996). Comparative studies on Xanthoria parietina, a pollution-resistant lichen and Ramalina duriaei, a sensitive species. I. Effects of air pollution of physiologocal processes." Lichenologist 28(4): 355–65.
  15. ^ Bačkor M, Fahselt D, Davidson R, Wu CT. (2003). "Effects of copper on wild and tolerant strains of the lichen photobiont Trebouxia erici (Chlorophyta) and possible tolerance mechanisms." Archives of Environmental Contamination and Toxicology 45: 159–67.
  16. ^ Brunialti G, Frati L. (2007). Biomonitoring of nine elements by the lichen Xanthoria parietina in Adriatic Italy: A retrospective study over a 7-year time span.Science of the Total Environment 387(1–3): 289-300.
  17. ^ Loppi S, Paoli L, Gaggi C. 2006). "Diversity of epiphytic lichens and Hg contents of Xanthoria parietina Thalli as monitors of geothermal air pollution in the Mt. Amiata area (Central Italy)."Journal of Atmospheric Chemistry 53(2): 93–105.
  18. ^ Solhaug KA, Gauslaa Y, Nybakken L, Bilger W. (2003). "UV-induction of sun-screening pigments in lichens." New Phytologist 158:91–100.
  19. ^ Solhaug KA, Gauslaa Y. (2004). "Photosynthates stimulate the UV-B induced fungal anthraquinone synthesis in the foliose lichen Xanthoria parietina." Plant Cell and Environment 27: 167–76.
  20. ^ Ivanova V, Schlegel R, Gräfe U (2000). "2-Methoxy-4,5,7-trihydroxy-anthraquinone, a new lichen metabolite produced by Xanthoria parietina". Pharmazie. 55 (10): 785–6. PMID 11082848. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  21. ^ Karagoz A, Aslan A. (2005). Antiviral and cytotoxic activity of some lichen extracts. Biologia 60(3): 281–6.
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