EPICUTICULAR AND INTRACUTICULAR WAXES - T HEIR SEPARATION, CHEMICAL CHARACTERISTICS AND ROLE IN CUTICULAR PERMEABILITY

The use of a cellulose nitrate film (with acetone 6% weight/volume) fa cilitated the stripping and recovery of the epi- and intracuticular wa xes from the two surfaces of Eucalyptus leaves. This study showed that depending on the species, the epicuticular wax (E. globulus) or the i ntracuticular 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 th e abaxial surface. The leaf aging process reduces the difference betwe en the surfaces, and induces a modification of the wax chemical compos ition. 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 biosynt hesis, e.g. trichloroacetic add, is supplied in the culture solution, the epicuticular a ax shows a large decrease in the polar fraction; an d correlates inversely with a decrease of beta Theta-dicetone in the a polar 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 fe w modifications in the proportions of the different alkanes. This phys iological effect of TCA, essentially observable at the level of the ch emical composition of the epicuticular wax, confirms that epi- and int racuticular wax biosynthesis pathways are different. Our technique of stripping permits us to study the water resistance of the different co mponents of isolated cuticle of Prunus laurocerasus and to show that a t the wax level, the intracuticular wax fraction is the main shield ag ainst water flow with a complementary role of the cutin matrix.