Response of oxidative metabolism in watermelon plants subjected to cold stress

The objective of the present work was to determine the effect of thermal stress on oxidative metabolism in Citrullus lanatus [Thomb.] Mansf. cv. Dulce maravilla. Plants were grown for 30 d at two temperatures (10 and 35˚C), at which time we measured the leaf concentration of antioxidant compounds (ascorbate, dehydroascorbate, reduced glutathione, oxidized glutathione) and enzymatic activities [superoxide dismutase (SOD), catalase, guaiacol peroxidase, ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase], as well as total hydrogen peroxide (H2O2) concentration and shoot dry weight. Our results indicate that chilling stress occurred in watermelon plants at 10˚C, while 35˚C is the optimal temperature for this plant. Low temperature stress caused: (i) decreased shoot weight; (ii) accumulation of H2O2; (iii) increased SOD activity; and (iv) decreased enzyme activities associated with detoxifying H2O2. The novelty of this study centres on the fact that so few cold-sensitive species have been examined to date — additional cold-sensitive species need to be studied to determine if there are shared characteristics in terms of how they respond to cold stress. Most studies have examined single antioxidant responses, whereas we conducted a comprehensive examination of many antioxidant responses.