RADIOLABELING STUDIES OF ISOLATED LEAF CUTICLES AFTER IN-VIVO INCORPORATION OF [C-14] ACETATE PRECURSOR IN IVY PLANTS

The radiolabelling of isolated leaf cuticles is determined after folia r or root application of [C-14]acetate precursor to ivy (Hedera helix L.] plants. Cuticle radioactivity, for a surface corresponding to abou t 36 leaves of different ages, represents 2.3 and 0.04% of the total r adioactivity recovered in the plant, 60 h after foliar or root applica tion of the precursor, respectively. Radioactivity is about twice as h igh in upper than in lower cuticles after the foliar treatment. The cu ticle radiolabelling, expressed in terms of unit surface area, greatly decreases as the leaf age increases, after either foliar or root appl ication of the precursor. The decrease is particularly severe for uppe r leaf cuticles when the precursor is applied to leaves. Radioactivity is incorporated both in cuticular waxes and in the insoluble part con stituted by the cutin polymer and polysaccharides. The proportion reco vered in cuticular waxes, in terms of surface area, increases with lea f age, therefore the inverse is observed for the insoluble part. The r adioactivity incorporation, expressed in relation to mass, is greater in waxes than in the insoluble part and decreases very sharply with in creasing leaf age. This approach should be Very useful to detect modif ications in cuticle formation resulting from biochemical inhibitors or external stress.