Cuticle on epidermis

Covers outer surface of the outer wall, hydrophobic

Possesses hydrophilic dendritic channels

The protective function of the epidermis is provided by the cuticle and epicuticular waxes which serve as a barrier to water and gases. The cuticle consists of special hydrophobic polymers represented by a mixture of cutins. Typically, it also supports a layer of epicuticular waxes.

In this transmission electron micrograph of willow (Salix fragilis) leaf epidermal outer wall, the cuticle is observed as a thick layer, in which there are a large number of hydrophilic branching (or dendritic) structures. They are continuous with the cell wall proper, but do not usually reach the outer surface. They are polysaccharides, and serve as channels for the transport of precursors of cutin and waxes during leaf development. In mature leaves they may be involved in the regulation of extra-stomatal transpiration.

In a dry atmosphere, the cuticle is a most effective barrier for the loss of water, but in a humid atmosphere, water is permitted to move across the cuticle. The dendrites are believed to aid in the control of this function. Small traces of epicuticular waxes can be observed at the surface of the cuticle.

C = cuticle; CP = cytoplasm; EW = epicuticular wax; PW = primary cell wall

Illustration courtesy of I. Kravkina, Komarov Botanical Institute, St. Petersburg, Russia