Epi- and intracuticular waxes: Their separation, chemical characteristics and role in cuticular permeability

The use of a cellulose nitrate film (with acetone 6% weight/volume) facilitated the stripping and recovery of the epi- and intracuticular waxes from the two surfaces of Eucalyptus leaves. This study showed that depending on the species, the epicuticular wax (E. globulus) or the intracuticular wax (E. gunnii) may be the predominant wax of the leaf. Generally speaking, the quantity of intracuticular wax is independent of the surface, but the epicuticular wax is always more abundant on the abaxial surface. The leaf aging process reduces the difference between the surfaces, and induces a modification of the wax chemical composition. The alkane component has a shorter chain length (disappearance of C-30 and C-31, and appearance of C-24 and C-26), with the presence of alkenes only in the mature leaves. When an inhibitor of was biosynthesis, e.g. trichloroacetic add, is supplied in the culture solution, the epicuticular a ax shows a large decrease in the polar fraction; and correlates inversely with a decrease of beta Theta-dicetone in the apolar fraction, only a decrease of the long chain alkanes (C-29 and C-31) correlates with an increase of the shorter chains (C-25 and C-27). In the intracuticular wax, the apolar fraction decreases, but with few modifications in the proportions of the different alkanes. This physiological effect of TCA, essentially observable at the level of the chemical composition of the epicuticular wax, confirms that epi- and intracuticular wax biosynthesis pathways are different. Our technique of stripping permits us to study the water resistance of the different components of isolated cuticle of Prunus laurocerasus and to show that at the wax level, the intracuticular wax fraction is the main shield against water flow with a complementary role of the cutin matrix.