Xyloglucanases in the interaction between the arbuscular mycorrhizal fungus Glomus mosseae and Rhizobium

We studied the production of xyloglucanase enzymes of leguminous roots in the presence of Rhizobium and arbuscular-mycorrhizal (AM) fungi. The AM fungus Glomus mosseae and Sinorhizobium meliloti GR4 for alfalfa, Rhizobium leguminosarum bv. viceae Rlv 13 for pea, R. leguminosarum bv. trifolli 2152 for clover, R. tropici CIAT 899 for bean and Mesorrhizobium mediterraneum USDA 3392 for chickpea. The inoculation of plants with G. mosseae, with Rhizobium or with both microorganisms together increased the shoot dry weights of almost all plants tested. The shoot dry weight of plants was higher when both symbionts were inoculated together than when they were inoculated separately and this benefit was related to the increase in the percentage of root length colonization and to the increase in the number of nodules observed in the joint inoculated plants. The AM fungus and Rhizobium increased the production of xyloglucanases in plant roots. The level of xyloglucanase activity and the number of xyloglucanolytic isozymes in plants roots inoculated with G. mosseae together with most of the Rhizobium tested was higher than when both microorganisms were inoculated separately. The possible relationship between xyloglucanase activities and the ability of AM and Rhizobium to improve the dry weight and AM root colonization of plants was investigated.