Abstracts |
Mycorrhiza formation is the consequence of a mutualistic interaction between
certain soil fungi and plant roots that helps to overcome nutritional limitations faced by the
respective partners. In symbiosis, fungi contribute to tree nutrition by means of mineral
weathering and mobilization of nutrients from organic matter, and obtain plant-derived
carbohydrates as a response. Support with easily degradable carbohydrates seems to be the driving
force for fungi to undergo this type of interaction. As a consequence, the fungal hexose uptake
capacity is strongly increased in Hartig net hyphae of the model fungi Amanita muscaria and
Laccaria bicolor. Next to fast carbohydrate uptake and metabolism, storage carbohydrates are of
special interest. In functional A. Muscaria ectomycorrhizas, expression and activity of proteins
involved in trehalose biosynthesis is mainly localized in hyphae of the Hartig net, indicating an
important function of trehalose in generation of a strong carbon sink by fungal hyphae. In
symbiosis, fungal partners receive up to similar to 19 times more carbohydrates from their hosts
than normal leakage of the root system would cause, resulting in a strong carbohydrate demand of
infected roots and, as a consequence, a more efficient plant photosynthesis. To avoid fungal
parasitism, the plant seems to have developed mechanisms to control carbohydrate drain towards
the fungal partner and link it to the fungus-derived mineral nutrition. In this contribution,
current knowledge on fungal strategies to obtain carbohydrates from its host and plant strategies
to enable, but also to control and restrict (under certain conditions), carbon transfer are
summarized. |