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	[[Image:carbon.jpg|thumb|300px| Diagram depicting the uptake, flow and utilization of carbon by host plant to AM fungi.<ref>http://shachar-hill.plantbiology.msu.edu/?page_id=44</ref>]]		[[Image:carbon.jpg|thumb|300px| Diagram depicting the uptake, flow and utilization of carbon by host plant to AM fungi.<ref>http://shachar-hill.plantbiology.msu.edu/?page_id=44</ref>]]
	===Applications===		===Applications===
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	====Genetics====		====Genetics====
	====Current Studies====		====Current Studies====

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Revision as of 14:29, 20 March 2013

Introduction to Mycorrhiza

"Mycor" - "rhiza" is derived from the Greek words meaning "fungus" - "root" ^[1]. This symbiotic relationship occurs underground between a fungus and the root system of vascular plants. Mycorrhiza colonize in host plant root systems either intracellularly(endomycorrhiza) or extracellularly(ectomycorrhiza). It is possible upon invasion that a weakly pathogenic relationship is established, and has been studied infrequently upon these rare occasions^[2]. However, commonly upon invasion a mutualistic relationship is established in which hundreds of thousands of fungal hyphael branches are formed from the vegitative mycelium, and extend outwards into the soil. Nutrients are often depleted in areas directly around plant roots, thus by Mycorrhiza extending the root zone over a large area nutrient uptake of water, nitrogen, and phosphorous is increased. In return, in order to provide root growth the host plant provides the mycorrhiza with the necessary carbohydrates such as glucose and sucrose ^[3].

Shows Ectomycorrhiza (extracellular) symbiosis with a plant root [4]

Shows Endomycorrhiza(intracellular) symbiosis with a plant root [5]

Although this scientific area of research is still ongoing, and only a small number of vascular plants has been examined 95% of them partake in this symbiotic relationship with Mycorrhiza^[7]

Contents 1 Endomycorrihza 1.1 Habitat 1.2 Reproduction and Growth 1.2.1 Life Cycle 1.2.2 Biochemical Pathways and Nutrient Uptake 1.3 Applications 1.3.1 Organic Farming 1.3.2 Truffles 2 Comparison Table 3 Environmental impacts and concerns 3.1 Forest communication 3.2 Acid Rain 3.3 Head 2 4 Additional Information 5 References

Endomycorrihza

Endomycorrizha are also known as arbuscular mycorrihizal (AM) fungi and are generally classified in the Zygomycota phylum^[8]. However, AM fungi lack the production of zygospores, which is a main and common characteristic of all fungi within Zygomycota. Therefore, according the AFTOL, AM fungi are apart of the Glomeromycota phylum^[8]. The Gloeromycota phylum contains 12 genra and 169 species^[8].Some of the other characteristics that define Glomeromycota are formation of arbuscules in plant roots and non-septate hypahe Previously mentioned, the AM fungi are characterized within the Glomeromycota because of their relatively large multi-nucleated spores that range from 40-800µm in diameter^[8]. These spores may be formed singly, in clusters or in fruiting bodies called sporocarps^[9].

Fungal arbuscules growing inside a living plant cell.[10]

Section of a sporocarp of Glomus sinuosum (isolate MD126, formerly Sclerocystis sinuosa). Spores are arranged around a center of interwoven hyphae and covered by a "peridium".[11]

Scientific Name Glomus sp. S328 Comments Spore of Glomus sp. S328 with attached hypha. Size Spore diameter is approximately 80 µm.[12]

Habitat

Endomycorrihza are most abundant in areas where there is a massive decline in soil nutrients that is accessible to the vegetation. In these conditions, AM fungi are more than often placed in poor soil conditions to aid in the growth and development of vegetation, more so agricultural crops^[8].Moreover, Endomycorrihza can be considered as ecologically important for most vascular plants and is found in 85% of plant families, most of them being crop species^{[13] [14]}

Reproduction and Growth

Life Cycle

To date, there is no evidence that proves that AM fungi produce sexually. Molecular genetic markers show that there is little to no recombination from different lineages, therefore supporting the notion that AM fungi reproduce asexually^[8]. The starting point of the AM fingi life cycle is the germination of the spore, which then either grows infection structures known as appresoria within the host plants' root system or grows hyphae from root to explore soil in order to uptake nitrogen. The appresoria move on the surface of host roots and forms hyphae between cells that penetrate cell walls ^[16]. This is the main reasons why AM fungi are not detrimental to the host plant because the hyphae grow only within the external membrane. These hyphae form coils or tree-like structures called arbuscules.

Biochemical Pathways and Nutrient Uptake

Endomycorrizhae have the ability to move carbon and nitrogen and utilize these molecules as an energy source.Carbon is transferred from the host plant to the internal mycelium of fungus in the form of hexose. Once within the fungi, hexose is then rearrange into glycogen and trehalose for short term storage. Then these forms of carbon are reconfigured into triacylglycerol (TAG) to be exported to the external mycelium system. TAG is then catabolized to be used at cell wall components via the glyoxylate cycle or as energy via the TCA cycle by the formation of ATP and amino acids. In this case, the fungi is using the host to benefit its’ growth.

However, when it comes to nitrogen, it functions in the opposite direction of the carbon flow. Inorganic nitrogen in the forms of ammonia (NH4+)and nitrate (NO3-) are absorbed by the external mycelium. These forms of nitrogen are not usable, thus they are assimilated and converted into Arginine; it is hypothesized that polyphosphate aids in this conversion. Arginine is then imported to the internal mycelium and catabolized further into [http:en.wikipedia.org/wiki/ammonium ammonium] (NH3+). Ammonium is a usable form of nitrogen for the fungus as well as the host plant. Ammonium is able to undergo many other chemical reactions and transformations that result in the production of ATP and amino acids. These end products are then, mainly, used by the host plant. In this case, the host plant is using the fungi to benefit its’ growth.

Applications

Organic Farming

The practice of organic farming generally excludes the use of harsh pesticides and fertilizer use, organic famers abide by the guidelines of the International Federation of Organic Agricultural Movements ^[19] . Because of these guidelines many organic fields have lower phosphorous and nitrogen concentration in the soil, have lower crop yields and are more prone to pests ^[20]. In organic farms phosphorus is usually the limiting factor of crop growth, not enough is available in the soil through weathering and other natural processes. Many farmers must use a complex mix of rotting material and manure in order to increase the nutrient value of the soil, endomycorrihza inoculation of crops helps to better utilize these nutrients and increases the yield on an organic farm ^[21] Low yield of an organic farm is one of the major downfalls to this method of farming when compared to traditional practices, therefore increasing crop yield is one of the biggest challenges facing organic farmers today. Certain species of endomycorrihza have been shown to increase growth rates of plants by stimulating the release of certain plant growth hormones such as cytokinins and gibberellins ^[22]

Truffles

Comparison Table

Environmental impacts and concerns

Forest communication

Mycorrhiza applications go far beyond just nutrient and water absorption and play a larger role in the forest community. Networks of Mycorrhiza can connect two trees of a different or similar species together forming vast networks throughout the forest floor ^[23]. Most forests are interconnected through these networks of mycorrhiza with the oldest trees forming the central hub of the network while the younger trees and seedlings become established in these pre made networks ^[24]. The underground networks actually help support saplings and younger weaker trees as carbon, nitrogen, water and other nutrients can be transferred through these networks from older more established trees "Mother trees" ^[25] . This transfer of nutrients back and forth throughout the forest floor can help these systems cope with climate changes such as unusually dry conditions.

Acid Rain

Acid rain is formed in the upper atmosphere as NO3 and SO2 are hydrolyzed ^[27] mixing with rain water and eventually falling back down to earth. Mycorrhizal associations can be affected either indirectly or through influence on host shoots. ^[28] Acid rain can have differeing effects on different species, one particular ECM fungi ascomycetes Cenococcum spp. has been reported to be more abundant in forests that have under gone acidification, most likely due to decreased competition from other species of fungi.^[29] The problem of acid rain is often compounded as an increase in PH leads to an increase in the rate that minerals dissolve such as toxic heavy metals. ^[30]

Head 2

Additional Information

Plant species that benefit from Endomycorrizha and Ectomycorrizha[1]

References

1. ↑ Frank, A. B. (1885). "Über die auf Würzelsymbiose beruhende Ehrnährung gewisser Bäum durch unterirdische Pilze". Berichte der Deutschen Botanischen Gesellschaft 3: 128–145.
2. ↑ Kirk, P. M.; Cannon, P. F.; David, J. C. & Stalpers, J. (2001). Ainsworth and Bisby’s Dictionary of the Fungi (9th ed.). Wallingford, UK: CAB International.
3. ↑ Harrison MJ (2005). "Signaling in the arbuscular mycorrhizal symbiosis". Annu Rev Microbiol. 59: 19–42. doi:10.1146/annurev.micro.58.030603.123749. PMID 16153162
4. ↑ Eco Tree Care and Conservation LTD. Mycorrhiza - The Biology A Study - What are Mycorrhiza and why are they important?http://www.ecotreecare.co.uk/mycorrhizal-inoculation-biology.htm
5. ↑ Eco Tree Care and Conservation LTD. Mycorrhiza - The Biology A Study - What are Mycorrhiza and why are they important?http://www.ecotreecare.co.uk/mycorrhizal-inoculation-biology.htm
6. ↑ Syekhfani, Prof. Dr. Ir. MS. (2013). Succession Life on Earth. Soil-Function
7. ↑ Trappe, J. M. (1987). Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint. Florida: CRC Press.
8. ↑ ^{8.0 8.1 8.2 8.3 8.4 8.5} Moore, D., Robinsion, G.D., & Trinci, A.P. (2011) 21st Century Guidebook to Fungi. Cambridge University Press, New York.
9. ↑ Redecker, Dirk. 2008. Glomeromycota. Arbuscular mycorrhizal fungi and their relative(s). Version 14 January 2008. http://tolweb.org/Glomeromycota/28715/2008.01.14 in The Tree of Life Web Project, http://tolweb.org/
10. ↑ http://shachar-hill.plantbiology.msu.edu/?page_id=44
11. ↑ Photo © Dirk Redecker, isolate courtesy of J. B. Morton at INVAM. Sporocarp diameter approximately 250 µm.
12. ↑ Copyright © 2000 American Association for the Advancement of Science Image Use restricted Attached to Group Glomeromycota: view page image collection Title s328_small.jpg Image Type Photograph Image Content Specimen(s) ID 7350 http://tolweb.org/Glomeromycota .
13. ↑ Gederman, H. A. Rev. Phytopath. 6, 397−418 (1968).
14. ↑ Wang, B.; Qiu, Y.L. (2006). "Phylogenetic distribution and evolution of mycorrhizas in land plants". Mycorrhiza 16 (5): 299–363. doi:10.1007/s00572-005-0033-6. PMID 16845554. Retrieved 2008-01-21.
15. ↑ http://shachar-hill.plantbiology.msu.edu/?page_id=44
16. ↑ Shchar-hil Lab doi:http://shachar-hill.plantbiology.msu.edu/?page_id=44
17. ↑ http://shachar-hill.plantbiology.msu.edu/?page_id=44
18. ↑ http://shachar-hill.plantbiology.msu.edu/?page_id=44
19. ↑ Stockdale, E.A., N.H. Lampkin, M. Hovi, R. Keatinge and E.K.M. Lennartsson et al., 2001. Agronomic and environmental implications of organic farming systems. Adv. Agron., 70: 261-262
20. ↑ Mahmood, I. Rizvi, R. Mycorrhiza and organic farming. (2010) Asian Journal of Plant Sciences, 9: 241-248
21. ↑ Mahmood, I. Rizvi, R. Mycorrhiza and organic farming. (2010) Asian Journal of Plant Sciences, 9: 241-248.
22. ↑ Mahmood, I. Rizvi, R. Mycorrhiza and organic farming. (2010) Asian Journal of Plant Sciences, 9: 241-248.
23. ↑ Beiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM. 2010. Architecture of the wood-wide web: Rhizopogon spp genets link multiple Douglas-fir cohorts. New Phytologist, 185: 543-553.
24. ↑ Beiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM. 2010. Architecture of the wood-wide web: Rhizopogon spp genets link multiple Douglas-fir cohorts. New Phytologist, 185: 543-553.
25. ↑ Beiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM. 2010. Architecture of the wood-wide web: Rhizopogon spp genets link multiple Douglas-fir cohorts. New Phytologist, 185: 543-553.
26. ↑ Mosquin, D. Mycorrhizal Networks.UBC Botanical Garden and Centre for Plant Research. (March 6 2010) http://www.botanicalgarden.ubc.ca/potd/2010/03/mycorrhizal_networks.php
27. ↑ Charlson, R.J., Rodhe, H., 1982. Factors controlling the acidity of natural rainwater. Nature 295, 683-685
28. ↑ Cairney,J. Meharg,A. Influences of anthropogenic pollution on mycorrhizal fungal.Environmental Pollution 106 (1999) 169-182
29. ↑ Danielson, R.M., Visser, S., 1989. Ef€fects of forest soil acidification on ectomycorrhizal and vesicular-arbuscular mycorrhizal development. New Phytologist 112, 41±47
30. ↑ Cairney,J. Meharg,A. Influences of anthropogenic pollution on mycorrhizal fungal.Environmental Pollution 106 (1999) 169-182