Arbuscular mycorrhizae

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Roseobacter sp. Courtesy of Harbour Branch Marine Microbial Database.

Classification

Eomycota

Domain:

Glomermycota

Phylum:

Glomeroycetes

Order:

Archaeosporales

Family:

Ambisporaceae

Genre:

Ambiospora

Family:

Archaeosporaceae

Genre:

Archaeospora Intraspora

Family:

Geosiphonaceae

Genre:

Geosiphon

Order:

Diversisporales

Family:

Acaulosporaceae

Genre:

Acaulospora Kuklospora Acaulospora

Family:

Entrophosporaceae

Genre:

Entrophospora

Family:

Gigasporaceae

Genre:

Gigaspora Scutellospora

Family:

Pacisporaceae

Genre:

Pacispora

Order:

Glomerales

Family:

Glomeraceae

Genre:=

Glomus

Order:

Paraglomerales

Family:

Paraglomaceae

Genre:

Paraglomus

Species:

Currently, the named species of arbuscular mycorrhizae fungi number over 200, but it is believed that there are over 2500 species which have not been identified as of yet (Martin et al, 1994).

Alternate names:

The term "vesticular- arbuscular mycorrhiza (VAM) was previously used to describe these fungi. However, because members of the Gigasporaceae do not form vesicles, "arbuscular mycorrhiza" is now a more widely accepted term.

Description and Significance

Arbuscular mycorrhizae are symbiotic relationships between specialized soil fungi and plant roots. The relationship between the plants and the fungi benefit the fungi and the plants by raising the quality of the soil and providing more access to available nutrients to each. Arbuscular mycorrhiza greatly improve the rate of growth in plants, especially in less than optimal conditions for plant growth. The extensive hyphal networks which the mycorrhiza form aid in the plants ability to access water and nutrients from the soil.

Arbuscular mycorrhizae are present and aid the growth of over 80% of plants species. They are present on all continents except for Antarctica. Many of the crop plants which are grown in current agricultural practices are aided by arbuscular mycorrhizae, and studies are being conducted to explore methods to improve yields through the inoculation of the crops with arbuscular mycorrhizae.

The extensive extaradical mycelium which the arbuscular mycorrhizae forms is responsible for extending the host plant's rooting network, providing a larger area with which to gain nutrients and water. The fungus invades the plant's root cells, expands it's mycelium which gains nutrients and provides them to the plant's cell, reproduces, then dies. The life cycle of the mycorrhizae cell is usually between 4 and 15 days, and when the fungus dies, the plant cell returns to normal (Moore, 2017).

Genome Structure

Arbuscular mycorrhizae form endosymbiosis with many plants and are simultaneously hosts to Mollicutes/ Mycoplasma related endobacteria [(Sun et al., 2018)]. Although they are very significant, genome information for arbuscular mycorrhizae and their Mycoplasma related endobacteria is currently sparse [(Sun et al, 2018)]. It is thought, however, that the evolution of arbuscular mycorrhizae and the colonization of land plants over 353- million years ago coincided, and that the mycorrhizae became more specialized to the plants where it formed [(Moore, 2017)].

Cell Structure and Reproduction

The most significant part of the cell structure of the arbuscular mycorrhizae is it's tree-like hyphal structures, known as its arbuscules, which deliver minerals and nutrients to its host plant. These nutrients are accepted by the host plant through a "plant derived periarbuscular membrane which surrounds the fungi's hyphae" and directs nutrients to the plant [(Gutjahr, 2013)]

The arbuscular mycorrhizae reproduce through spores which the hyphae produce. The act of reproduction through spores is the method with which the plant is supplied additional nutrients and minerals from the soil [(Rossouw, 2017)]. Through this process, the plant gains access to carbon, phosphorus, water, and other nutrients that it would otherwise be unable to gain [(Rossouw, 2017)].

Ecology

Arbuscular mycorrhizae interact with other organisms, almost all plants, throughout all of the stages of their lives. Approximately two-thirds of all of the land plants on earth interact with arbuscular mycorrhizae [(Hodge, 2000)]. This group of fungi are found in the soils of all of the continents on Earth, with the exception of Antarctica. The main threats to the fungi are human activity and the changing climate [(Rossouw, 2017)].

Future potential for use in bioremediation

The role that arbuscular mycorrhizae plays in nature by sharing a symbiotic relationship with plants is that is aids the plants in stabilizing and removing minerals from the soil. In turn for providing access to these minerals, the fungus receives carbon from the plant. Recent research shows that by inoculating plants with arbuscular mycorrhizae aids the plants in the removal and stabilization of heavy metals which contaminate the soil.

References

[Gutjahr, 2013. https://www.semanticscholar.org/paper/Cell-and-developmental-biology-of-arbuscular-Gutjahr-Parniske/c8ee97c7c49031c6e5f08cec44ca57fc69660163]

[Hodge, 2000. https://academic.oup.com/femsec/article/32/2/91/528677]

[Martin et al, 1994. David Moore's World of Fungi: where mycology starts. www.davidmoore.org.uk/Assets/Mostly_Mycology/Diane_Howarth/am.htm]

[Rossouw, 2017. https://www.sanbi.org/animal-of-the-week/arbuscular-mycorrhizal-fungi/]

[Sun et al, 2018. https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.15472]