Urea penetration of isolated tomato fruit cuticles

14C-urea penetration of isolated tomato (Lycopersicon esculentum Mill. cv. 'Pik Red') fruit cuticular membranes(CM) was studied as a function of concentration and temperature. There was no significant effect of cuticular wax on urea penetration at 25C, permeances for the CM being 8.4 X 10(-10) and dewaxed CM (DCM) 11.1 X 10(-10) m.s-1. Time lags were near zero for both CM and DCM. Steady-state diffusion analysis suggests that the relatively low cuticular permeance of urea is due to low partitioning that offsets high diffusivity. Urea flux through the CM and DCM showed approximately 1.5- and 1.9-fold increases, respectively, for each 10C increase between 5 and 45C. Urea flux across CM and DCM increased linearly with concentration (10 micromolar to 1 M) and, thus, was a first-order process