Determination of diffusion coefficients of octadecanoic acid in isolated cuticular waxes and their relationship to cuticular water permeabilities

Transport properties of cuticular waxes from 40 different plant species were investigated by measuring desorption rates of C-14-labelled octadecanoic acid from isolated and subsequently reconstituted wax, Diffusion coefficients (D) of octadecanoic acid in reconstituted waxes, calculated from the slopes of the regression lines fitted to the linearized portions of desorption kinetics, ranged from 1.2 x 10(-19) m(2) s(-1) (Senecio kleinia leaf) to 2.9 x 10(-17) m(-2) s(-1) (Malus cf, domestica fruit), Cuticular water permeabilities (cuticular transpiration) measured with intact cuticular membranes isolated from 24 different species varied from 1.7 x 10(-11) m s(-1) (Vanilla planifolia leaf) up to 2.1 x 10(-9) m s(-1) (Malus cf. domestica fruit), thus covering a range of more than 2 orders of magnitude. Cuticular water permeabilities were highly correlated with diffusion coefficients of octadecanoic acid in isolated cuticular wax of the same species, It is therefore possible to estimate cuticular barrier properties of stomatous leaf surfaces or of leaves where isolation of the cuticle is impossible by measuring D of octadecanoic acid in isolated waxes of these leaves.