EFFECT OF ELEVATED COPPER ON THE ULTRAVIOLET LIGHT-ABSORBING COMPOUNDS OF CUCUMBER COTYLEDON AND LEAF TISSUES

Abstract

The effect of copper [Cu(II)] on the ultraviolet light-absorbing compounds of cucumber (Cucumis sativus L., cv Poinsett 76) leaf and cotyledon tissues was investigated. Tissue disks (7 mm) were exposed to CuSO4 · 5H2O concentrations from 50 μM (12.5 ppm) to 2.5 mM (625 ppm) at either pH 6.0 or 4.5 for up to 48 h in both light and dark. Acidified, aqueous methanol extracts (flavonoid-rich fraction) were analyzed by high performance liquid chromatography. Copper(II) altered the levels of the UV-absorbing compounds (340 nm), increasing the levels of some compounds at low Cu(II) concentrations and decreasing the levels of the UV-absorbing compounds at higher Cu(II) levels. In most cases, the magnitude of the Cu(II)-induced changes in cucumber phenolics was dependent upon tissue type, light condition, pH, and treatment duration. Since plant leaf phenolic compounds extracted under these conditions may have antioxidative activity, the ability to chelate prooxidative minerals and protect against ultraviolet B radiation, the Cu(II)-induced changes in phenolic compounds may modify plant responses to environmental stresses and alter the nutritional values of certain vegetable crops.