Structural changes and permeability of ivy (Hedera helix L.) leaf cuticles in relation to leaf development and after selective chemical treatments

Abstract

. 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.

Atomic force microscopy study of isolated ivy leaf cuticles observed directly and after embedding in Epon®

“…Figure 1 a shows a top view of a transverse section of ivy cuticle embedded in Epon, The general shape of an isolated cuticle can be easily recognized, as corresponding images obtained by light microscopy are very similar (Viougeas et aL, 1995). The outside of the cuticle is regular and bordered by a dark zone which corresponds to a fracture that is always found on this side between Epon and the cuticle (Fig, 1 a, arrow).…”

“…The surface profile in Figure 16 shows surface irregularities which are not revealed by transmission electron microscopy (TEM) (HoUoway, 19826;Gouret et al, 1993;Viougeas et al, 1995), Views of such transverse sections in TEM are implicitly assumed to be flat. The relief observed here, which has been magnified in Figure 1 b (compare the continuous line to the dotted one), is due to the cutting process which is not ideal but might reflect the intimate structure of the material.…”

“…Data obtained for the same samples by electron microscopy and AFM are compared. Ivy was chosen because its cuticle can be easily separated from the leaf and because we have used it as model to investigate the relationship between the structure and permeability of isolated cuticles (Gouret, Rohr & Chamel, 1993;Viougeas, Rohr& Chamel, 1995).…”

Cloning and Characterization of the WAX2 Gene of Arabidopsis Involved in Cuticle Membrane and Wax Production

“…First, exhaustive extraction of waxes from cuticles does not alter cuticle membrane ultrastructure, except for a slight reduction in the visibility of cuticle proper lamellae (Viougeas et al, 1995). Second, the cuticle membranes of seven wax mutants in sorghum and five wax mutants in Arabidopsis, including cer1, were ultrastructurally normal (Jenks et al, 1994;M.A.…”

Ontogenetic and seasonal development of wax composition and cuticular transpiration of ivy ( Hedera helix L.) sun and shade leaves

“…From the literature (Haas 1977;Viougeas et al 1995) and our own preliminary experiments we knew that cutin development and wax composition of ivy (Hedera helix L.) changed signi®cantly with increasing leaf age. Thus, we investigated the development of the wax composition and the cuticular transpiration of ivy leaves in parallel, in order to ®nd a possible correlation between wax composition and cuticular permeability.…”