Co-Permeability of 3H-Labeled Water and14C-Labeled Organic Acids across Isolated Plant Cuticles1

Penetration of 3H-labeled water (3H2O) and the 14 C-labeled or- ganic acids benzoic acid ((14C)BA), salicylic acid ((14C)SA), and 2,4-dichlorophenoxyacetic acid ((14C)2,4-D) were measured simul- taneously in isolated cuticular membranes of Prunus laurocerasus L., Ginkgo biloba L., and Juglans regia L. For each of the three pairs of compounds (3H2O/( 14 C)BA, 3H2O/( 14 C)SA, and 3H2O/( 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 3H2O/( 14 C)BA, co-permeability was measured with isolated cuticles of nine other plant species. Permeances of 3H2 Oo f all 12 investigated species were highly correlated with the per- meances of (14C)BA (r2 5 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 cutic- ular transport physiology in future investigations.