PERMEABILITY OF PERIDERM AND CUTICULAR MEMBRANES TO ALKALI CATIONS

The rates of penetration of alkali cations through isolated potato per iderm and pear fruit cuticular membranes as a function of pH and the e xternal solution concentration were determined. Steady-state rates wer e measured using a diaphragm diffusion cell, and permeabilities and th e corresponding diffusion coefficients were calculated from the lag ti me. The observed penetration rates of the alkali cations in the peride rm and cuticular membranes were in the order Cs+ > K+ > Na+ > Li+. Thi s is the order of increasing crystal radii and the order of decreasing exchange selectivity. The diffusion coefficients of all counterions i ncreased as the external concentration was increased. (C) 1995 Academi c Press, Inc.