Penetration of Ions through Isolated Cuticles

Abstract

Penetration of radioactive cations (Ca45, Rb86) and anions (S35O4, Cl36) through enzymically isolated cuticles of tomato fruit, having no stomatal pores, and green onion leaves, with stomatal pores, was studied. The permeability of these cuticular membranes from the outer surface to the inner surface, as compared to movement from the inner to outer surface was much greater for Ca++, Rb+, SO4- and Cl-. These differences were greater in the tomato fruit cuticle, which lacks stomata, than in the cuticle of the green onion leaf, which possesses stomata. A dialyzing membrane showed no differences in permeability for ions originating at the 2 surfaces. Rate of penetration through different cuticular surfaces was directly related to the extent of ion binding on the surface which was opposite the site of initial entry. It is possible that the greater ion binding on the inside, compared to the outside, of isolated cuticular membranes facilitates foliar absorption.