β-1,3-glucanase activities in tomato roots inoculated with arbuscular mycorrhizal fungi and/or Phytophthora parasitica and their possible involvement in bioprotection

beta-1,3-Glucanases in tomato roots were studied after arbuscular mycorrhizal (AM) symbiosis establishment and/or pathogenic infection by Phytophthora parasitica by polyacrylamide gel electrophoresis (PAGE). Two species of AM fungi, Glomus mosseae and Glomus intraradices were tested, and Phytophthora inoculation was performed on both non-mycorrhizal and mycorrhizal tomato pre-colonized for 4 weeks with either of the AM fungal species. The protective effect of both AM fungi on tomato plants against Phytophthora was assessed. In control roots two acidic beta-1,3-glucanase isoforms were constitutively expressed, and their activity was higher in mycorrhizal roots. Two additional acidic isoforms were detected in extracts from G. mosseae-colonized tomato roots, but not in G. intraradices-colonized roots. Roots infected by P. parasitica displayed stronger activities but the pathogen did not induce the isoforms related to G. mosseae colonization. Only one basic glucanase isoform was detected whether the plants were non-inoculated or colonized by any of the fungi when inoculated singly. However, when plants were pre-inoculated with G. mosseae and post-infected with P. parasitica two additional basic isoforms were clearly revealed. Results are discussed in relation to the possible role of the additional acidic and basic beta-1,3-glucanase isoforms in the establishment and development of the AM symbiosis, as well as their putative implication in plant bioprotection. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.