Thermodynamics of the water permeability of plant cuticles: characterization of the polar pathway

The water permeability of cuticles isolated from the leaves of 14 plant species was measured at temper-atures from 10 8C to 55 8C at 5 K intervals. Permeances increased slightly with temperatures <35 8C and drastically in the higher temperature range. The data were analysed according to the Arrhenius formalism which led to distinct plots for the lower and higher temperature range, respectively. Activation energies of permeation for the lower temperature range were estimated to amount to 15.2–52.5 kJ mol21, at higher temperature activation energies ranged from 52.2– 117.3 kJ mol21. This thermodynamics approach is used for further elucidating the pathway taken by water across the plant cuticle. Based on the results of this study it is hypothesized that the diffusion of water occurs along polysaccharide strands crossing the cuticle and that the transport properties of these polar pathways change with temperature