Co-permeability of 3H-labelled water and 14C-labelled organic acids across isolated Prunus laurocerasus cuticles: Effect of temperature on cuticular paths of diffusion

Abstract

Co-permeability of 3H-labelled water and 14C-labelled benzoic acid or 2,4-dichlorophenoxyacetic acid across isolated cuticular membranes of Prunus laurocerasus L. was measured at temperatures ranging from 15 to 50°C. The water and benzoic acid permeances were highly correlated over the whole temperature range investigated, whereas water and 2,4-dichlorophenoxyacetic acid permeances were only correlated between 15 and 30°C. The activation energies of cuticular permeability calculated from Arrhenius plots were 40 kJmol-1 for water and benzoic acid and 115 kJ mol-1 for 2,4-dichlorophenoxyacetic acid. The slopes of the Arrhenius plots of 2,4-dichlorophenoxyacetic acid were linear between 15 and 50°C, whereas pronounced phase transitions around 30°C were observed for water and benzoic acid permeability. However, with isolated polymer matrix membranes, where cuticular waxes forming the transport-limiting barrier of cuticles have been extracted, phase transitions were not observed for water and benzoic acid. It is concluded that temperatures above 30°C caused structural changes in the transport-limiting barrier of the cuticles leading to additional paths of diffusion for water and benzoic acid but not for 2,4-dichlorophenoxyacetic acid.