Co-Permeability of (3)H-Labeled Water and (14)C-Labeled Organic Acids across Isolated Plant Cuticles

Penetration of (3)H-labeled water ((3)H(2)O) and the (14)C-labeled organic acids benzoic acid ([(14)C]BA), salicylic acid ([(14)C]SA), and 2,4-dichlorophenoxyacetic acid ([(14)C]2,4-D) were measured simultaneously in isolated cuticular membranes of Prunus laurocerasus L., Ginkgo biloba L., and Juglans regia L. For each of the three pairs of compounds ((3)H(2)O/[(14)C]BA, (3)H(2)O/[(14)C]SA, and (3)H(2)O/[(14)C]2,4-D) rates of cuticular water penetration were highly correlated with the rates of penetration of the organic acids. Therefore, water and organic acids penetrated the cuticles by the same routes. With the combination (3)H(2)O/[(14)C]BA, co-permeability was measured with isolated cuticles of nine other plant species. Permeances of (3)H(2)O of all 12 investigated species were highly correlated with the permeances of [(14)C]BA (r(2) = 0.95). Thus, cuticular transpiration can be predicted from BA permeance. The application of this experimental method, together with the established prediction equation, offers the opportunity to answer several important questions about cuticular transport physiology in future investigations.