Some cesium and potassium salts increase the water permeability of astomatous isolated plant cuticles

Salts were applied as aqueous solution to the outer surfaces of astomatous isolated cuticles, and the water was allowed to evaporate. Effects of salt residues on the surfaces of cuticles on water permeability of cuticles were measured at 25°C. A surface dose of 0.2 mol m^–2 Cs₂CO₃ and K₂CO₃ increased the water permeability of pear leaf cuticles by factors of 9.9 and 3.9, respectively. Na₂CO₃ was barely effective, and Li₂CO₃ as well as (NH₄)₂CO₃ had no influence on water permeability. Potassium applied as sulfate, nitrate, or chloride had no effect on the water permeability of pear leaf cuticles, while K⁺ salts of weak acids (0.2 mol m^–2) were effective, as they increased water permeability by factors of 5.4 (K⁺‐acetate), 3.9 (K₂CO₃), and 2.0 (K₂HPO₄), respectively. Sensitivity of Idesia polycarpa leaf cuticles to treatment with K₂CO₃ at 0.2 mol m^–2 was greatest as water permeability was increased 35‐fold, while the water permeability of cuticles from other species tested (astomatous leaf cuticles from Hedera helix, Citrus aurantium, Prunus laurocerasus, Pyrus communis, and Populus canescens; fruit cuticles from Capsicum annuum and Lycopersicon esculentum) increased only by factors ranging from 1.7 to 3.9. Data are discussed in relation to swelling and ion‐exchange properties of cuticles.