Inhibition of the K⁺-Stimulated ATPase of the Plasmalemma of Pinto Bean Leaves by Ozone

Three varieties of Phaseolus vulgaris which differ in their sensitivity to ozone were examined for changes in some physiological and structural plasma membrane characteristics. Plasma membrane vesicles were prepared from control and ozone-treated (0.2 to 0.5 microliters per liter ozone for 5 hours) leaf tissue, and the (K+ + Mg2+)-ATPase activity determined and compared. No major changes were observed in the resistant varieties. The sensitive variety showed a severe inhibition of ATPase activity which was largely due to a decrease in the K+-stimulated component. This inhibition was completely reversed by the addition of sulfhydryl compounds. Ozone-induced plasma membrane permeability changes may be effected by damage to membrane proteins, perhaps by oxidation of amino acid sulfhydryl groups to disulfide and sulfenic moieties.