RADIOLABELING OF ISOLATED CUTICLES FROM FOLIAR DISCS USED AS A TEST OF CUTICLE BIOSYNTHESIS

The radiolabelling of isolated Hedera helix L. (ivy) leaf cuticles was investigated after incorporation of [C-14]acetate in foliar discs. Cu ticle radioactivity greatly decreased as leaf age increased. The perce ntage of radioactivity incorporated in the upper cuticles decreased fr om 0.5% to 0.08% of the total radioactivity of foliar discs from young to old leaves. Cuticle radioactivity was recovered in waxes, cutin an d polar components. It was considerably greater for waxes when express ed in terms of cuticle mass. The methodology was validated using S-eth yl-dipropylthiocarbamate (EPTC). The radioactivity incorporation in cu ticles was significantly reduced when 1 mM EPTC was deposited as a 20- mu L droplet on to foliar discs 6 h before the incorporation of radiol abelled acetate. EPTC inhibited radiolabelling of wax and cutin fracti ons in the upper and lower cuticles. Some acetylenic fatty acid analog ues inactivating lauric and oleic acid omega-hydroxylases, used as aci d and sulphonate forms in the same experimental conditions as EPTC, in duced no reduction in cuticle radiolabelling. An inhibitory effect was observed only for the acetylenic and the saturated C-12 fatty acid an alogues, used as tetrabutylammonium sulphonates, when applied directly in the liquid medium supporting foliar discs. Several assumptions are considered to explain the results of the present investigation.