PRESENCE OF XYLOGLUCAN-HYDROLYZING GLUCANASES (XYLOGLUCANASES) IN ARBUSCULAR MYCORRHIZAL SYMBIOSIS

We studied the production of xyloglucan-hydrolyzing glucanases (xylogl ucanases) in roots of lettuce (Lactuca sativa), onion (Allium cepa) an d soybean (Glycine max) colonized by the arbuscular mycorrhizal (AM) f ungus Glomus mosseae. Endoxyloglucanase activity in mycorrhizal roots extracted with 100 mM Tris-HClH (pH 7) was higher than in nonmycorrhiz al root extracts. There were no significant differences in endoxyloglu canase activity between mycorrhizal and nonmycorrhizal roots when they were extracted with 200 mM Na2PO4 (pH 7.2), 100 mM NaCl, 100 mM potas sium-phosphate buffer (pH 7.8) or 25 mM. MES (Na) (pH 6.6). From the r esults obtained the most suitable extraction buffer for endoxyloglucan ase activity in lettuce plants was 100 mM Tris-HCl (pH 7). Endoxyloglu canase activity was greatest when the reaction was carried out at pH 5 or 8, and activity declined at pH 3, 4, 6, 7 and 9. Maximum endoxylog lucanase activity was observed in a range oi: temperatures between 37 degrees C and 50 degrees C. Tris extracts of mycorrhizal plants showed more endo- and exoxyloglucanase activity than nonmycorrhizal plants w hen nasturtium or tamarind xyloglucan was used as the substrate. Extra cts from spores and external mycelia of G. mosseae also showed endo- a nd exoxyloglucanase activity. The possible participation of xyloglucan ase activity in the colonization of plant roots by AM fungus is discus sed.