HEAT STRESS-INDUCED ALTERATIONS IN ANTIOXIDATIVE ENZYMES OF SOME PLANTS OF CUCURBITACEA FAMILY

The effects of high temperatures on melon cvs. Miranda and Poli, watermelon cv. Crimson Tide and zucchini cv. Asma leaves. The leaves obtained from plants were subjected to 35, 40, 45, 50, 55 and 60°C temperatures with gradual increments every 30-minutes. Samples, obtained at each treatment, were analyzed for ascorbic acid content, NADP(H) oxidase, catalase, gluthatione reductase, peroxidases activities and isoperoxidase patterns. The ascorbic acid content slightly increased parallel to temperature increment in zucchini but did not change in watermelon and in both melon cultivars. Melon cv. Poli exhibited comparatively less oxidative damage than cv. Miranda with a lower NAD(P)H oxidase activity. Heat stress induced NAD(P)H activity in watermelon and zucchini comparing to control plants. Results revealed that antioxidative enzyme activities were increased generally up to 50°C then decreased gradually in melon cultivars. Besides cv. Poli generally had higher enzyme activities than cv. Miranda. The activity of catalaes become prominent in watermelon while the activity of ascorbate peroxidase become prominent in zucchini. Acidic isoperoxidase bands with different relative mobility values were found in all species. Besides, basic isoperoxidase band could not be determined in both melon cultivars and watermelon while a basic isoperoxidase band was found in zucchini.