Copper-induced Damage to the Permeability Barrier in Roots of Silene cucubalus

Abstract

The mechanism of copper-induced damage to cell plasma membrane functioning in intact roots of Silene cucubalus was studied by comparing the effects of high copper ion concentrations with those of Nethylmaleimide (NEM), a sulfhydryl-reagent, and of cumene hydroperoxide (CHP), an organic peroxide known to induce lipid peroxidation by free radical formation. Leakage of potassium ions from roots (a measure of cell permeability) was detected directly upon supply of copper or NEM, whereas with CHP a 45 minutes time-lag was observed. In copper or CHP treated plants, leakage was constant for at least three hours and, as demonstrated by trypan blue staining after a 24 hour exposure, the plasma membranes of root cells were severely damaged, especially in the tips. A marked increase of lipid peroxidation products was detected in roots treated with these reagents, although the increase was highest with copper. In contrast, with NEM potassium leakage diminished after about 1 hour, dye staining of root cells was negligible and the level of lipid peroxidation products did not increase. When NEM plus CHP were added, the results were the same as those obtained with high copper supply, suggesting a combined effect of thiol depletion and lipid peroxidation by copper ions. In addition, it was shown in vitro that copper ions stimulate lipid peroxidation in microsomes isolated from roots of plants grown at a normal low copper supply. These results suggest that, apart from thiol depletion, direct free radical formation leading to lipid peroxidation might play an important role in the mechanism of copper-induced damage to the permeability barrier in roots of higher plants in vivo.