Water permeability of plant cuticles

Publisher Website
Google Scholar
Abstract
Using the system vapor/membrane/liquid, permeability coefficients of cuticular transpiration (Pct) were determined as functions of water activity in the vapor (awv). Enzymatically isolated cuticular membranes (CM) of Citrus aurantium L. and nonisolated CM of onion bulb scales and eggplant fruits were investigated. Pct of Citrus and eggplant CM decreased with decreasing awv, while permeability coefficients of CM of onion were independent of awv. Extraction of soluble cuticular lipids (SCL) from the CM of Citrus increased permeability coefficients by a factor of approximately 500. This extraction had no effect on the dependence of Pct on awv. Treating cuticular membranes as a resistance network consisting of SCL and the polymer matrix, it is shown that the permeability of onion CM is determined by the resistance of the SCL arranged in series with the polymer matrix. In this type of CM liquid and vapor are separated by a continuous, nonporous layer of SCL, and the driving force of transpiration is the gradient of partial pressure of water vapor across the SCL layer. In the CM of Citrus and eggplant, the SCL layer is traversed by polar pores that swell or shrink depending on awv. However, liquid continuity is maintained across these membranes down to awv=0.22, the lowest value used. In this type of membrane the driving force of transpiration is the water potential gradient across the membrane.