. SUMMARYThe fine .structure of ivy leaf cuticles was investigated as a function of leaf development before and after cuticle isol-dtion as well as after selective extraction of cuticle components. Cuticle mass increased with increasing age from 234-3 to S39-1 //g cm"^. Waxes increased from 12-3 to 18-6",, of cuticle mass from young to old leaves. However, percentages of cutin and non-lipid constituents did not vary significantly with leaf age. They represented approx. 58 and 26",, of the cuticle mass, respt'ctivcly. Cuticle thickness determined from flectron and light microscopy increased 12-fold during leaf growth to reach 4-25 //m for mature leaves. Transmission electron microscopy of transverse sections of non-isolated and isolated cuticles showed an outer lamellate zone gradually merging from an inner reticulate zone the thickness of which increased with leaf growth. The lamellate zone appeared very early (ill 7'itro unexpanded leaf) and was characterized by a constant thickness (0-2 //m). Cuticle lamellation seemed to disappear after extraction of soluble cuticular wax, which confirmed intracuticular wax localization in lamellae. Electron-dense fibrillae observed in the reticulate zone disappeared after acid hydrolysis showing that they are made of non-lipid components. X-ray diffraction confirmed the presence of crystalline 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 with increasing loat age. sugRcsting that the main harrier to diffusion is the outer lamellate zone. A considerable increase in isoproturon penetration through cuticles resulted from the wax extraction, demonstrating tbe major role of wax in tbe control of cuticular permeability to this herbicide.

SummaryThe radiolabelling of isolaled Hedera helix L, (ivy) leaf cutieles was investigated after incorporation of [14C]acetate in foliar discs Cuticle radioactivity greatly decreased as leaf age inereased. The percentage of radioactivity incorporated in the upper cuticles decreased from 0.5% to 0.08% of the total radioactivity of foliar dises from young to old leaves. Cuticle radioactivity was recovered in waxes, cutin and polar components. It was considerably greater for waxes when expressed in terms of cuticle mass. The methodology was validated using S‐ethyl‐dipropylthiocarbamate (EPTC). The radioactivity incorporation in cuticles was significanly reduced when 1 mm EPTC was deposited as a 20‐μL droplet on lo foliar dises 6 h before the incorporation of radiolabelled acetate. EPTC inhibited radioiabelling of wax and cutin fractions in the upper and lower cuticles. Some acetylenic fatty acid analogues inactivating lauric and oleic acid ω‐hydroxylases, used as acid and sulphonate forms in the same experimental conditions as EPTC, induced no reduction in cuticle radiolabelling. An inhibitory effect was observed only for the acetylenic and the saturated C12 fatty acid analogues, used as tetrabu‐tylammonium sulphonates, when applied directly in the liquid medium supporting foliar dises. Several assumptions are considered to explain the results of the present investigation.