Cuticular layer/polymer

Suberin and the related polymer, cutin, function primarily as the structural components of barrier layers, which always have waxes associated with them (231, 232). Studies with isolated cuticular layers showed that the wax provides the major barrier to moisture diffusion Removal of the wax resulted in a 300- to 2000-fold increase in permeability (292, 398, 401). Similar studies with cuticular layers from the leaves of Citrus aurantium demonstrated that wax provides the... 

Plants were probably the first to have polyester outerwear, as the aerial parts of higher plants are covered with a cuticle whose structural component is a polyester called cutin. Even plants that live under water in the oceans, such as Zoestra marina, are covered with cutin. This lipid-derived polyester covering is unique to plants, as animals use carbohydrate or protein polymers as their outer covering. Cutin, the insoluble cuticular polymer of plants, is composed of inter-esterified hydroxy and hydroxy epoxy fatty acids derived from the common cellular fatty acids and is attached to the outer epidermal layer of cells by a pectinaceous layer (Fig. 1). The insoluble polymer is embedded in a complex mixture of soluble lipids collectively called waxes [1], Electron microscopic examination of the cuticle usually shows an amorphous appearance but in some plants the cuticle has a lamellar appearance (Fig. 2). 

Cuticle constitutes the boundary between higher plants and their environment. Therefore, this layer might be expected to play an important role in the interaction of the plant with environmental factors. The plant cuticle is composed almost entirely of lipids and the role of some of these lipids in the interaction between plants and microbes has become clear in the recent years. In this brief review, we shall confine our discussion to two specific examples of such interactions a detrimental one with pathogenic fungi and a beneficial one with phyllospheric bacteria which might provide fixed nitrogen in return for the use of some of the cuticular components as the carbon source. In this context, we will deal only with the role of the insoluble lipid-derived polymer, cutin, but not the role of soluble waxes that are always constituents of the cuticle. 

---