Effect of Elevated Iron on Ultraviolet Light-Absorbing Compounds of Cucumber Cotyledon and Leaf Tissues

Abstract

The effect of iron [Fe(II)] on ultraviolet light-absorbing phenolic compounds of cucumber (Cucumis sativus L., cv Poinsett 76) leaf and cotyledon tissues was investigated. Tissue disks (7 mm) were exposed to increasing FeSO 4 · 7H 2 O concentrations from 25 µM (7 ppm) to 500 µM (143 ppm) at pH 4.0-7.0 for 24 h in both light and dark. Acidified, aqueous methanol extracts that contain various phenolic compounds were analyzed by high performance liquid chromatography. Depending upon the treatment pH, Fe(II) altered the levels of the UV light-absorbing compounds measured at both 270 and 340 nm, increasing the levels of some compounds at low Fe(II) concentrations, which were subsequently reduced at higher Fe(II) levels. In most cases, the Fe(II)-induced change in phenolic compound concentration was dependent upon tissue type, light condition, and pH. The dose-response relations and pH dependencies for the Fe(II)-induced changes were complex. These results ORDER REPRINTS CALDWELLsuggest that the FeSO 4 · 7H 2 O treatments may specifically alter certain metabolic processes and do not simply produce reactive oxygen, which degrade the phenolic compounds.