CUTICULAR LIPIDS OF TERRESTRIAL PLANTS AND ARTHROPODS: A COMPARISON OF THEIR STRUCTURE, COMPOSITION, AND WATERPROOFING FUNCTION

Abstract

Summary1. Lipids deposited on the surface or embedded within the cuticle of terrestrial plants and arthropods are primarily responsible for the observed low rates of water loss through the cuticle.2. These lipids are a mixture of long‐chain compounds which include hydrocarbons (saturated, unsaturated, branched), wax esters, free fatty acids, alcohols, ketones, aldehydes, and cyclic compounds.3. The cuticle of both plants and arthropods is a continuous, non‐cellular multilayered membrane which overlies the epidermal cells.4. In arthropods, horizontal division of the cuticle into layers is clearly visible. In plants, the layers comprising the cuticle are not sharply demarcated.5. The substance responsible for the structural integrity of the plant cuticle (cutin) is composed of cross‐esterified fatty acids; structural integrity in arthropod cuticle is provided by a chitin‐protein complex.6. Cuticular lipids are probably formed near the surface in both plants and arthropods; however, specific sites of synthesis are known for only a few species and little is known about their transport from these sites to the surface. The elaborate pore canal and wax canal system of arthropod cuticle is absent from plants.7. The physical structure and arrangement of the lipid deposits on the cuticular surface that are so important in controlling water movement depend on both quantity and chemical composition, and are, in turn, specific to each species in relation to its environment.8. Different lipid components are not equally efficient in reducing transpiration. Maximum waterproofing effectiveness is provided by long‐chain, saturated, non‐polar molecules containing few methyl branches.9. Plants and arthropods can, within genetic constraints, alter the composition of their cuticular waxes to improve impermeability when conditions require increased water conservation.10. None of the models proposed to explain the change in arthropod cuticular permeability which occurs at a species‐specific temperature (‘transition temperature’) in many species is supported by the experimental data now available.