Radiolabelling of isolated cuticles from foliar discs used as a test of cuticle biosynthesis

The 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 m m 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.