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AM Fungi in Plants and Soil Questions

Question 1

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Answer 1

Four features indicate that the host controls colonisation. Total colonisation of the root system is prevented; the fungus never enters the stele. The initiation of colonisation is reduced to a single penetration point from multiple appressoria. Thirdly, the fungus must pass through passage cells of the hypodermis. Finally, different types of AM are associated with specific hosts.

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Question 2

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Answer 2

Arum types have extensive intercellular spaces, and more regular cell arrays in the cortex. Paris type colonies appear to have tighter junctions between cells. Thus physical barriers are likely to prevent intercellular spread in Paris-type hosts. However, oxygen availability might also be important.

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Question 3

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Answer 3

AM fungi are heterotrophic. They rely utterly on their host for organic carbon. Penetration of the root probably requires an expenditure of energy by the fungus. Thus it seems likely that the fungus must gain energy from the root before commencing lateral spread.

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Question 4

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Answer 4

Except for passage cells, the outer layer of the hypodermis is suberised soon after formation. The loss of exudates from the root is thus limited to a proportion of the surface. This limited area of nutrient loss may attract hyphae of AM fungi. Secondly, the cell becomes suberised soon after penetration, thus further limiting penetration by all fungi, yet maintaining control over the mineral uptake provided by the AM fungi. This is likely to reduce attack by pathogens, and enable longer periods where the cortex is used for nutrient exchange.

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Question 5

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Question 6

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Question 7

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