ION-EXCHANGE SELECTIVITIES OF PERIDERM AND CUTICULAR MEMBRANES TOWARDALKALI CATIONS

The ion-exchange selectivities of lithium, sodium, potassium, and cesi um on isolated potato periderm (Solanum tuberosum) and pear fruit cuti cular membranes were investigated; the general order of preference bot h for cation selectivities and ion-exchange capacities was lithium > s odium > potassium > cesium. The potato periderm and pear fruit cuticul ar membranes exhibited a behavior typical of ion-exchange resins of th e weak acid type. At constant pH 7, the ion-exchange capacities of per iderm and cuticular membranes increased with hydrated ionic radius, an d also with increasing pH and neutral salt concentration, and decrease d with crystal ionic radius. Counterion selectivities also exhibited t he same behavior. The ion-exchange properties are discussed in terms o f the structure and function of potato periderm and pear fruit cuticul ar membranes.