TEMPERATURE STRESS TOLERANCE AND INCREASE IN ANTIOXIDATIVE ENZYME ACTIVITIES IN MYCORRHIZAL STRAWBERRY PLANTS

Promotion of active oxygen synthesis in plants occurs under several stress conditions and antioxidative enzymes have relationships with the resolution. We investigated the changes in activities of antioxidative enzymes (SOD, APX) through symbiosis with arbuscular mycorrhizal (AM) fungi in strawberry plants under high temperature stress. Strawberry (Fragaria × ananassa Duch., cv. Nohime) runner plants were inoculated with two species of AM fungi. Ten weeks after AMF inoculation, plants were transferred under 35°C-constant temperature and raised during the following 10 days. Dry weight of shoots and roots became greater in AM plots than in the non-AM ones 10 weeks after inoculation. The level of mycorrhizal colonization differed between the fungi. Browning of leaves and roots appeared following 10 days under stress conditions, but the severity of browning was diminished in AM plots than in the non-AM ones. Before the stress conditions were imposed, SOD activities differed little among the plots except in lateral roots with colonization. In non-AM plot, SOD activities markedly decreased under stress conditions. However, AM plots showed higher SOD activities than the non-AM one especially after 10 days under stress condition; the effect differed with plant parts; little difference appeared between the fungi. On the other hand, APX in AM plots became higher in roots before stress and especially after ten days under stress condition; Glomus mosseae showed relatively higher values than Gigaspora margarita. From these findings, tolerance to high temperature stress and the increase in activities of SOD and APX occurred in mycorrhizal strawberry plants, so that the activation of antioxidative enzymes is thought to be associated with the temperature stress tolerance.