Xyloglucan endotransglycosylase activities in onion roots colonized by the arbuscular mycorrhizal fungus Glomus mosseae

We studied the production of xyloglucan endotransglycosylase (XET; EC 2.4.1.-) activity during the process of penetration and development of the arbuscular mycorrhizal (AM) fungus Glomus mosseae in roots of onion (Allium cepa, cv. Babosa). Viscometry assays did not yield any detectable transglycosylation products; however, a radiochemical assay showed that in both mycorrhizal and nonmycorrhizal plants XET activity decreased as the root grew. Xyloglucan endotransglycosylase activity was higher in mycorrhizal plants than in nonmycorrhizal plants. The possible role of XET associated with wall loosening in the colonization of the plant root by AM fungi is discussed.