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 (UY-BBE) radiation. The latter irradiance corresponded to a decrease in stratospheric ozone of ca 20% for clear sky conditions at Beitsville, MD on 21 June. The diamine putrescine and the polyamine 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, Poinsett 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. (author)