STRUCTURAL-CHANGES AND PERMEABILITY OF IVY (HEDERA-HELIX L) LEAF CUTICLES IN RELATION TO LEAF DEVELOPMENT AND AFTER SELECTIVE CHEMICAL TREATMENTS

The fine structure of ivy leaf cuticles was investigated as a function of leaf development before and after cuticle isolation as well as aft er selective extraction of cuticle components. Cuticle mass increased with increasing age from 234.3 to 539.1 mu g cm(-2). Waxes increased f rom 12.3 to 18.6% of cuticle mass from young to old leaves. However, p ercentages of cutin and non-lipid constituents did not vary significan tly with leaf age. They represented approx. 58 and 26% of the cuticle mass, respectively. Cuticle thickness determined from electron and lig ht microscopy increased 12-fold during leaf growth to reach 4.25 mu m for mature leaves. Transmission electron microscopy of transverse sect ions of non-isolated and isolated cuticles showed an outer lamellate z one gradually merging from an inner reticulate zone the thickness of w hich increased with leaf growth. The lamellate zone appeared very earl y (in vitro unexpanded leaf) and was characterized by a constant thick ness (0.2 mu m). Cuticle lamellation seemed to disappear after extract ion of soluble cuticular wax, which confirmed intracuticular wax local ization in lamellae. Electron-dense fibrillae observed in the reticula te zone disappeared after acid hydrolysis showing that they are made o f non-lipid components. X-ray diffraction confirmed the presence of cr ystalline structures and revealed a cuticle disorganization after wax extraction. Permeability measurements showed an increase rather than a decrease in glyphosate and isoproturon diffusion through cuticles wit h increasing leaf age, suggesting that the main barrier to diffusion i s the outer lamellate zone. A considerable increase in isoproturon pen etration through cuticles resulted from the wax extraction, demonstrat ing the major role of wax in the control of cuticular permeability to this herbicide.