Abstract
Most of the aerial organs of vascular plants are covered by a protective layer known as the cuticle, the main purpose of which is to limit transpirational water loss. Cuticles consist of an amphiphilic polyester matrix, polar polysaccharides that extend from the underlying epidermal cell wall and become less prominent towards the exterior, and hydrophobic waxes that dominate the surface. Here we report that the polarity gradient caused by this architecture renders the transport of water through astomatous olive and ivy leaf cuticles directional and that the permeation is regulated by the hydration level of the cutin-rich outer cuticular layer. We further report artificial nanocomposite membranes that are inspired by the cuticles’ compositionally graded architecture and consist of hydrophilic cellulose nanocrystals and a hydrophobic polymer. The structure and composition of these cuticle-inspired membranes can easily be varied and this enables a systematic investigation of the water transport mechanism.
Highlights
Most of the aerial organs of vascular plants are covered by a protective layer known as the cuticle, the main purpose of which is to limit transpirational water loss
We originally expected that the directional water transport behavior of olive cuticles is mainly caused by the lipophilic waxes that are preferentially located towards the outer cuticular side, and the hydrophilic polysaccharides at the interior of the cuticles (Fig. 1b)
A hydrophobic polymer matrix was used in lieu of the non-polar waxes and lipophilic portions of cutin, hydrophilic cellulose nanoparticles assume the function of the cuticular polysaccharides, and the polar portions of the cutin matrix were omitted (Fig. 1c)
Summary
Most of the aerial organs of vascular plants are covered by a protective layer known as the cuticle, the main purpose of which is to limit transpirational water loss. The water transport characteristics of the SBS/CNC membranes were investigated as a function of direction, CNC content, membrane thickness, and relative humidity at the donor side (RHD) using gravimetric dry (for RHD = 75 and 85%) and wet cup (for RHD = 100%) methods (Fig. 2a, b and Supplementary Fig. 8a, b).
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