Effect of xyloglucan and xyloglucanase activity on the development of the arbuscular mycorrhizal Glomus mosseae

The effect of xyloglucan on spore germination, hyphal length and mycorrhiza l colonization of alfalfa plants was studied. The presence of high concentr ations of xyloglucan in the rooting medium inhibited mycorrhizal colonizati on in plants inoculated with Glomus mosseae. Intermediate xyloglucan concen trations had no effect on arbuscular mycorrhizal (AM) colonization, but a l ow concentration increased mycorrhization of host plants. The effects of th ese doses on spore germination and hyphal length of G. mosseae were similar to those observed for mycorrhizal colonization. Production of xyloglucanas e was assayed during colonization by the AM fungus G. mosseae in lettuce an d onion. Endoxyloglucanase activity peaked 15 d after inoculation, whereas exoxyloglucanase activity peaked at 30 and 50 d. Extracts from external myc elia of G. mosseae showed endo- and exoxyloglucanase activities. Some of th e endoxyloglucanase activities detected in AM colonized plant roots may be derived from the AM fungus, as endoxyloglucanase proteins found in the exte rnal mycelia of G, mosseae and in mycorrhizal root extracts showed similar electrophoretic mobility. These results suggest: that xyloglucanase is invo lved in the process of colonization of plants by G, mosseae.