ULTRASTRUCTURE AND RADIOLABELING OF LEAF CUTICLES FROM IVY (HEDERA-HELIX L) PLANTS IN-VITRO AND DURING EX-VITRO ACCLIMATIZATION

Cuticle ultrastructure and radiolabelling of isolated cuticles after i ncorporation of [C-14] acetate in foliar discs were investigated with ivy plants grown in vitro then ex vitro. Results show an increase in t hickness, mass and wax content, between young and expanded leaves, for both in vitro and ex vitro cuticles. The cuticle of in vitro unexpand ed leaves was very thin and only constituted a lamellate zone. The ult rastructure of in vitro young and expanded leaf cuticles showed charac teristics similar to in situ cuticles. The thickness of the lamellate zone remained fairly constant and represented 33% of the cuticle thick ness in young leaves, but only 11.4% in expanded leaves. The number of lamellar units decreased from 14 to nine between these two growth sta ges. The main difference between young leaves developed in vitro or ex vitro was a thinner lamellate zone for ex vitro cuticles. However. th ese latter cuticles had an intermediary zone between the lamellate and reticulate zones. The cuticle thickness of expanded leaves was greate r for in vitro cuticles suggesting a temporary decrease in cuticle bio synthesis after transfer of the plant from in vitro to ex vitro. Resul ts from cuticle radiolabelling show higher radioactivity incorporation in cuticles isolated from leaves developed ex vitro compared to in vi tro. This radiolabelling was particularly marked for ex vitro young le af cuticles and depended on the duration of the ex vitro growth period revealing a progressive activation of cuticle biosynthesis in respons e to new environmental conditions (C) 1997 Annals of Botany Company.