The leaf surface
Virtually all primary aerial plant parts are covered by a cuticle. It’s as if leaves, petioles, flowers and young stems were wrapped in a kind of cling film that helps keep water in and bugs out. Cuticles consist in the main of a polymeric network of esterified hydroxy fatty acids (the cutin) shot through with polysaccharide fibres and impregnated with waxes. Everything in this structure is highly variable when cuticles from different plants or plant parts are compared, but the waxes are the most variable component of all.
“Waxes” is a generic term for all compounds in the cuticle that can be dissolved in organic solvents; the polymer is insoluble. While the cutin polymer and polysaccharide fibres form a solid extracellular matrix it is the waxes that are responsible for most of the barrier properties of the cuticle. Waxes reside on the surface of the cuticle and may be observed by scanning electron microscopy if they form crystallites, but they also reside within the cuticle where they are at least as important for the cuticular barrier properties as their epicuticular counterparts.
Unfortunately, the relationships between wax composition or their appearance under the scanning electron microscope and permeability of the cuticle to water or anything else are still very poorly understood. This is also true for the questionable effect on cuticular barrier properties of the frequently observed accelerated deterioration of epicuticular waxes when plants are exposed to significant concentrations of air pollutants.
Please refer to the abstracts supplied with the list of publications for details of our own work on plant cuticles.
I started a web page in the mid-nineties that listed homepage addresses of people working with cuticles and provided links to freely available abstracts, of which there were relatively few then, in many areas of cuticular research. As in the meantime practically all abstracts are freely available I stopped updating this page some time ago but it is still available if anyone’s interested: