Pectinaceous layer

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). 

The cuticle, being attached to the epidermal cells via a pectinaceous layer, can be released by disruption of this layer by chemicals such as ammonium oxalate/oxalic acid or by pectin-degrading enzymes. After treatment of the recovered cuticular layer with carbohydrate-hydrolyzing enzymes to remove the remaining attached carbohydrates, the soluble waxes can be removed by ex-... 

For removal of the cuticle from plant tissues, it is necessary to disrupt the pectinaceous layer external to the epidermal cell wall. In addition, carbohydrates attached to the cuticle have to be removed. A combination of enzyme (pectinase, cellulase) and chemical (ammonium oxalate-oxalic acid, cuprammonium ion and ZnCl2-HCl) treatments is usual (Matic, 1956 Eglinton and Hunneman, 1968 Walton and Kolattukudy, 1972). Waxes associated with the cuticle can be removed by extraction with organic solvents. 

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