The use of ion‐selective microelectrodes for measuring calcium and hydrogen ion transfer between foliar surfaces and simulated rain solutions

Abstract

summaryA method is presented for the rapid and quantitative assessment of the transfer of calcium (Ca2+) and hydrogen (H+) ions between the surface of a leaf and simulated acidic rain. A small volume (144 μl) of pH 3.5 simulated rain solution was confined within a rigid, Teflon capillary on the foliar surface. A liquid membrane‐type, neutral carrier‐based, ion‐selective microelectrode either for Ca2+or for H* was placed within the capillary with the tip of the microelectrode at least 100μm from the foliar surface. This allowed spatial and temporal aspects of ion gradients generated by ion diffusion from the foliar surface to be studied. Results indicate that, throughout a 60–minute period after contact of simulated rain with the adaxial foliar surface of spinach (Spinacea oleracea L. cv. Marathon) or Japanese pachysandra (Pachysandra terminalis Siebold & Zucc)., negligible amounts of foliar‐derived calcium diffused into the simulated rain solution, and there was virtually no neutralization of the pH 35 rain simulant present in the capillary. A discussion of these results with respect to previous methods of investigation and theoretical possibilities of ion diffusion and cuticular permeability is presented.