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Summary Cucumber (Cucumis sativus L. cv. Marketer) plants were treated with 0 or 100μg of soil-applied uniconazole (20 ml of 17μM solution) and then exposed to a gaseous sulfur dioxide pulse one week following treatment. Uniconazole-treated plants exhibited considerably less visible sulfur dioxideinduced phytotoxicity than untreated controls. Rates of net photosynthesis 24h following sulfur dioxide exposure were 0 and 5.6μmol CO2 m-2s-1 for the control and treated plants, respectively. Forty-eight hours following sulfur dioxide exposure, net photosynthesis in uniconazole-treated plants recovered to 10.4μmol CO2 m-2s-1 but remained near zero in controls. The foliar content of malondialdehyde, a by-product of lipid peroxidation, was about 30% less in uniconazole-treated plants compared to controls following exposure to sulfur dioxide. This indicates that uniconazole decreased sulfur dioxide-induced lipid peroxidation. Stomatal diffusive resistance measurements suggested that increased sulfur dioxide tolerance in uniconazole-treated plants was not due to stomatal closure. The content or activity of several antioxidant systems including glutathione, peroxidase, and catalase was increased in uniconazole-treated plants. These results suggest that uniconazole-induced sulfur dioxide tolerance may be due, at least in part, to increased antioxidant activity which reduces stress-related oxidative cellular damage. |
