Quantitative characterization of cuticular barrier properties: methods, requirements, and problems

The interface between the atmosphere and leaves and fruits is formed by the lipophilic plant cuticle, which seals the outer epidermal cell walls, thus significantly reducing water loss and uptake of dissolved solutes deposited on the cuticle surface. Different experimental and theoretical approaches for quantifying barrier properties of cutinized leaf and fruit surfaces are presented and discussed in this review. Quantitative characterization of cuticle barrier properties requires (i) the measurement of diffusion kinetics, namely the amount diffusing versus time, (ii) accurate knowledge of driving forces, namely concentration gradients, acting across the barrier, and (iii) the calculation of permeances, namely diffusion velocity. We suggest that on the basis of permeances, which are independent from experimental boundary conditions such as driving forces, the time period of measurement, and area, cuticle barrier properties of different plant organs, different plant species, and different lines, as well as barrier properties of suberized root tissue or synthetic membranes, can be directly compared. This review provides a short and easy to understand manual on what should be kept in mind when quantifying barrier properties of cutinized and suberized transport barriers. This could be helpful for scientists working on cuticle biosynthesis and its regulation.