The role of cuticular waxes in the penetration of a hydrophilic ([‘4C]glyphosate) and a lipophilic ([‘4C]isoproturon)
compound through isolated plant cuticles was investigated using a finite-dose diffusion system (dropletkuticlelagar), after
partial or complete soluble wax extraction. Cuticle models were selected from leaves (Ibex aquifofium, Hedera helix. Ficus elus-
tica) and fruit (Lycnpersicon esculentum, Capsicum ~nltuum). These cuticles represent two types of microstructure characterized
by the presence or absence of a lamellar zone above a reticulate zone. The diffusion of glyphosate through the cuticle was very
low for the five species. Wax extraction increased diffusion rate slightly, although it still remained very limited even after
complete wax extraction. The diffusion of isoproturon depended to a large extent on the plant species: the highest values were
obtained for pepper and tomato cuticles. Extraction of superficial waxes led to a considerable increase in the diffusion rate of
this herbicide through the cuticle of these two species. More pronounced wax extraction increased the transfer through holly
cuticles by a factor of 4, although cuticles still contained 70 %a of cuticular waxes. After complete wax extraction, transcuticular
penetration reached 93 % of the applied dose after 96 h for this species, but only 34.6 and 75.2 % for rubber and ivy cuticles.
respectively. This lower transfer rate was observed for cuticles having a lamellar zone above the reticulate zone. Results show
that waxes are not always the main barrier to the penetration of chemicals through plant cuticles, and that k is necessary to
consider the complete picture of cuticle organization with the polymer matrix and waxes. 0 Elsevier, Paris.