The properties of the leaf cuticle—the outermost layer of the leaf—are of special interest because of their potential to be used to improve crops.
The permeability of the cuticle is an important variable affecting the rate at which leaves lose water in dry conditions, even when their stomata are closed. Low permeability is presumably an important adaptation to arid conditions.
Permeability is also strongly temperature dependent, so it is especially crucial under hot, dry conditions.
Cuticle thickness and permeance together constitute permeability. Variation in the chemical composition of cuticles drives variation in their permeance.
Physical reinforcement of leaves is an important adaptation to aridity and, especially, to low soil nutrients—crucial in Australian conditions. Tough leaves can defend the plant against herbivores and pathogens. Cuticle thickness contributes substantially to leaf fracture toughness, which is also influenced by cutan, a major chemical constituent of the cuticle.
Surface features of the cuticle are also important, affecting the ability of pathogens to attach to leaf surfaces; of water to bead; of the leaf to act as a self-cleaning surface; and of pesticides and other chemicals to be effective.
