REASSESSMENT OF THE ROLE OF CUTICULAR WAXES IN THE TRANSFER OF ORGANIC-MOLECULES THROUGH PLANT CUTICLES

The role of cuticular waxes in the penetration of a hydrophilic ([C-14 ]glyphosate) and a lipophilic ([C-14]isoproturon) compound through iso lated plant cuticles was investigated using a finite-dose diffusion sy stem (droplet/cuticle/agar), after partial or complete soluble wax ext raction. Cuticle models were selected from leaves (Ilex aquifolium, He dera helix, Ficus elastica) and fruit (Lycopersicon esculentum, Capsic um annuum). These cuticles represent two types of microstructure chara cterized by the presence or absence of a lamellar zone above a reticul ate zone. The diffusion of glyphosate through the cuticle was very low for the five species. Wax extraction increased diffusion rate slightl y, although it still remained very limited even after complete wax ext raction. The diffusion of isoproturon depended to a large extent on th e plant species: the highest values were obtained for pepper and tomat o cuticles. Extraction of superficial waxes led to a considerable incr ease in the diffusion rate of this herbicide through the cuticle of th ese two species. More pronounced wax extraction increased the transfer through holly cuticles by a factor of 4, although cuticles still cont ained 70% of cuticular waxes. After complete wax extraction, transcuti cular 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, respecti vely. This lower transfer rate was observed for cuticles having a lame llar zone above the reticulate zone. Results show that waxes are not a lways the main barrier to the penetration of chemicals through plant c uticles, and that it is necessary to consider the complete picture of cuticle organization with the polymer matrix and waxes. (C) Elsevier, Paris.