Main Page

From BIOL 2P96 Jan 2013 Group 03

Revision as of 12:25, 16 March 2013 (edit) Bt09sg (Talk | contribs) ← Previous diff		Revision as of 12:30, 16 March 2013 (edit) (undo) Bt09sg (Talk | contribs) Next diff →
Line 60:		Line 60:
	==References==		==References==
	<ref>Frank, A. B. (1885). "Über die auf Würzelsymbiose beruhende Ehrnährung gewisser Bäum durch unterirdische Pilze". Berichte der Deutschen Botanischen Gesellschaft 3: 128–145.</ref>		<ref>Frank, A. B. (1885). "Über die auf Würzelsymbiose beruhende Ehrnährung gewisser Bäum durch unterirdische Pilze". Berichte der Deutschen Botanischen Gesellschaft 3: 128–145.</ref>
		+	<ref>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.</ref>.
		+	<ref>Trappe, J. M. (1987). Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint. Florida: CRC Press.</ref>

---

Revision as of 12:30, 16 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.

Figure 1. The photo on the left depicts a vascular plant engaging in a symbiotic Mycorrhizal relationship therefore increasing the total root area, and allowing a maximum nutrient uptake. The photo on the right depicts a vascular plant that does not engage in a Mycorrhizal relationship therefore producing a smaller total root area, and in turn receiving a smaller nutrient uptake.

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^[3]

Contents 1 Endomycorrihza 1.1 Habitat 1.2 Reproduction and Growth 1.2.1 Life Cycle 1.2.2 Biochemical Pathways 1.3 Applications 1.3.1 Genetics 1.3.2 Current Studies 2 Ectomycorrihza 2.1 Habitat 2.2 Reproduction and Growth 2.2.1 Life Cycle 2.2.2 Biochemical Pathways 2.3 Applications 2.3.1 Genetics 2.3.2 Current Studies 3 Comparison Table 4 Environmental concerns 4.1 Acid Rain 4.2 Head 2 5 Additional Information 6 References

Endomycorrihza

Endomycorrizha are also known as arbuscular mycorrihizal (AM) fungi and are generally classified in the Zygomycota phylum^[4] 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.^[5] The Gloeromycota phylum contains 12 genra and 169 species ^[6].

Habitat

Endomycorrihza are most abundant in areas where there is a massive decline in soil nutrients that is accessible to the vegetation. This is due to their purpose of invading hosts plants and aiding in nutrient retrieval^[7]. 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^{[8] [9]}

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 ^[10].

This diagram dipicts the life cycle of AM fungi. The starting point is the germinating spore, which then either grows infection structures known as appresoria or grows hyphae from root to explore soil. The appresoria move on the surface of host roots and forms hyphae between cells that penetrate cell walls ^[11]. This is one of 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. The picture below illustrates what AM fungi look inside of a host root cell.

Some of the other cahracteristics 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^[12]. These spores may be formed singly, in clusters or in fruiting bodies called sporocarps^[13]. Below are graphics depicting a sporocarp and spores of Glomus sinosum.

Biochemical Pathways

Applications

Genetics

Current Studies

Ectomycorrihza

Habitat

Reproduction and Growth

Life Cycle

Biochemical Pathways

Applications

Genetics

Current Studies

Comparison Table

Environmental concerns

Acid Rain

Acid rain is formed in the upper atmosphere as NO3 and SO2 are hydrolyzed ^[14] mixing with rain water and eventually falling back down to earth. Mycorrhizal associations can be affected either indirectly or through influence on host shoots. ^[15] 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.^[16] 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. ^[17]

Head 2

Additional Information

Plant species that benefit from Endomycorrizha and Ectomycorrizha[1]

References

^{[18] [19]}. ^[20]