INFLUENCE OF UV-B RADIATION ON POLYAMINES, LIPID-PEROXIDATION AND MEMBRANE-LIPIDS IN CUCUMBER

Sensitive (Poinsett) and insensitive (Ashley) cultivars of cucumber (Cucumis sativus) were grown for four weeks from planting in unshaded greenhouses at 0 or 12.2 kJ m-2 day-1 of biologically effective ultraviolet-B (UV-B(BE)) radiation. The latter irradiance corresponded to a decrease in stratospheric ozone of ca 20% for clear sky conditions at Beltsville, MD on 21 June. The diamine putrescine and the polyamine spermidine spermidine accumulated in cotyledon and leaf tissues in response to UV-B radiation in both cultivars, but levels were not correlated with sensitivity to UV-B. Lipid peroxidation, as quantified by measurement of malondialdehyde (MDA), was increased by UV-B exposure. Significant cultivar differences were observed, with increases in lipid peroxidation in both cotyledons and leaves being correlated with UV-B sensitivity. Determination of membrane lipid composition indicated slight decreases in the unsaturated/saturated fatty acid ratios as a result of UV-B exposure. In general, Pionsett had a lower unsaturated/saturated ratio of fatty acids than did Ashley. These results indicate that membrane lipids may be a target of UV-B damage and that differences in the UV-B susceptibility of these two cultivars may involve differences in lipid metabolism. Polyamine accumulation in response to UV-B radiation stress is consistent with similar responses to other environmental stressors.