Cleavage of sucrose in roots of soybean (Glycine max) colonized by an arbuscular mycorrhizal fungus

Here we tested the hypothesis that the activity of sucrose-cleaving enzymes is modified in roots colonized by arbuscular fungi. The activities of soluble and cell-wall bound invertases and of sucrose synthase were assessed in nonnodulated roots of soybean (Glycine max), either inoculated with the arbuscular mycorrhizal fungus Glomus mosseae, or in the absence of inoculation. Furthermore, we assessed the activity of sucrose-cleaving enzymes in cultured extraradical mycelium of the arbuscular fungus Glomus intraradices. Both soluble and cell wall-bound acid invertase activities decreased during the course of the experiment; there were no differences between mycorrhizal and nonmycorrhizal plants. Alkaline invertase activity was significantly higher in inoculated roots from the beginning of root colonization. Sucrose synthase activity showed no significant differences between treatments for 35 d, thereafter it became significantly higher in mycorrhizal roots. No sucrose cleaving activities were detected in extraradical mycelium. Fungal colonization of soybean roots induces an increase in alkaline invertase activity, which could provide hexoses for the fungal symbiont and for development of colonized cells.