UNICONAZOLE-INDUCED THERMOTOLERANCE IN SOYBEAN SEEDLING ROOT-TISSUE
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Soybean [Glycine max(L.) Merr. cv. A2] seeds were germinated in 0 or 1 mg 11 (3.4 uM) uniconazole, after which seedling roots were excised and exposed to 22 or 48C for 90 min. Prior to the temperature treatments there were few ultrastructural differences between uniconazoletreated seedling roots and the controls. Following exposure to 48C, electron micrographs revealed near complete loss of normal ultrastructure in control epidermal root cells, whereas cellular integrity was maintained in treated roots, indicating that uniconazole conferred tolerance to high temperature. Total electrolyte, sugar and K+ leakage were all greater from control roots than treated roots during exposure to 48C. Proline content in the roots was unaffected by uniconazole at 22C but was 2530% greater in treated tissue than in controls following exposure to 48C. Malondialdehyde content was unaffected by uniconazole at 22C but was nearly 20% less in treated tissue than in controls following high temperature exposure. This indicates that uniconazole decreased hightemperatureinduced lipid peroxidation. Uniconazole elevated several antioxidant systems in the roots, including watersoluble sulfhydryl concentration and catalase, peroxidase and superoxide dismutase activities. These findings are consistent with the hypothesis that uniconazoleinduced stress tolerance is due, at least in part, to enhanced antioxidant activity which reduces stressrelated oxidative damage to cell membranes. Copyright 1990, Wiley Blackwell. All rights reserved
