Diffusion and Electric Mobility of KCI within Isolated Cuticles of Citrus aurantium

Fick's second law has been used to predict the time course of electrical conductance change in isolated cuticles following the rapid change in bathing solution (KCI) from concentration C to 0.1 C. The theoretical time course is dependent on the coefficient of diffusion of KCI in the cuticle and the cuticle thickness. Experimental results, obtained from cuticles isolated from sour orange (Citrus aurantium), fit with a diffusion model of an isolated cuticle in which about 90% of the conductance change following a solution change is due to salts diffusing from polar pores in the wax, and 10% of the change is due to salt diffusion from the wax. Short and long time constants for the washout of KCI were found to be 0.11 and 3.8 hours, respectively. These time constants correspond to KCI diffusion coefficients of 1 × 10⁻¹⁵ and 3 × 10⁻¹⁷ square meters per second, respectively. The larger coefficient is close to the diffusion coefficient for water in polar pores of Citrus reported elsewhere (M Becker, G Kerstiens, J Schönherr 1986] Trees 1: 54-60). This supports our interpretation of the washout kinetics of KCI following a change in concentration of bathing solution.