Abstract. The water sorption by cuticular membranes (CM) isolated from both leaves and fruit and representing different structural and chemical cuticular types, was measured over the whole range of relative humidities using a magnetic suspension microbalance. The sorption isotherms were generally not linear and sorption increased more rapidly at the highest values of relative humidity. The highest values of water content, at 80–99% r.h., measured for the seven species ranged from 1.1 to 7.7% of the dehydrated weight. Extraction of the soluble cuticular lipids did not result in a decrease of sorption, but only in a lower interspecific dispersion. There was a drastic reduction (63%) in water sorption when polymer matrix membranes (MX) were partially acid‐hydrolysed; but methylation or charging with iron of (MX) did not have any significant effect on water sorption. The data obtained are discussed in relation to cuticular permeability. Two determinants of water permeability were determined: the partition coefficient (K) relating the equilibrium Water concentration of the cuticle to that of the surrounding atmosphere; and the diffusion coefficient (D), calculated from the half‐times of the sorption process in kinetic measurements.

This article is the first one of a series aimed at determining the numerous interaction configurations adopted by H 2 O molecules in macromolecular systems, using infrared spectrometry. These configurations are important for understanding the role of water in such systems, particularly biosystems. This article concerns H 2 O molecules at low concentration in an isolated plant cuticle. The analysis of quantitative variations of the entire spectrum due to modifications of chosen parameters such as stage of growth, humidity of the surrounding atmosphere, and temperature shows that two types of interaction configurations exist for H 2 O molecules hydrogen bonded to surrounding molecules: There are "volatile" molecules held by one hydrogen bond they formed with receptor sites of the cuticle and "embedded" molecules held by two stronger or three hydrogen bonds which are part of the hydrogen bond network of the cuticle. Embedded molecules do not evaporate, even at 100 °C. We emphasize the conditions which should be fulfilled in order to extend such a method to other macromolecular systems.

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. 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.