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There are very few studies of hormonal regulation of arbuscular mycorrhiza formation that include the gaseous hormone ethylene. Ethylene is considered inhibitory to the formation of arbuscular mycorrhizae; however, very low concentrations may promote their formation. We used an improved method of exogenous ethylene application to determine whether ethylene concentration dependent changes in colonization occur in the leek (Allium porrum L. cv. Giant Musselburgh) – Glomus aggregatum Schenck & Smith emend. Koske system. This improved method allowed for a continuous flow of constant concentration of the gas to be applied to a substrate. The 0.6 μL/L substrate–ethylene treatment reduced both root and leaf length and resulted in significantly lower arbuscular colonization compared with controls, whereas the 0.3 μL/L treatment reduced root length only and did not significantly affect colonization levels. Despite continuous application of exogenous ethylene, the amount of ethylene detected in inoculated substrates was reduced to near zero 20 days after inoculation. This decrease may be either due to an increased capacity for ethylene oxidation by arbuscular mycorrhizal roots or because arbuscular mycorrhizal fungi (or other microbes in the pot-cultured inoculum) are capable of metabolizing ethylene. The present study highlights the need for investigations into arbuscular mycorrhizal fungal physiology and the mechanisms by which ethylene regulates arbuscular mycorrhiza formation.


This article was originally published in Canadian Journal of Botany, 80(2): 114-119. © 2002 National Research Council. Reproduced with permission