Analysis of Epicuticular Waxes

Abstract

The plant surfaces which are exposed to the atmosphere, such as leaves, stems, fruits, and petals, are covered with a hydrophobic, water repellent substance called wax, of which the leaf waxes have received most attention. The outer surface of leaf epidermis is covered with a substance called cutin which is usually impregnated with wax; together they comprise the cuticle. The insoluble polymer cutin is composed of cross-linked hydroxy fatty acids (Kolattukudy 1975), which are released upon hydrolysis. The wax is a complex mixture of lipophilic substances such as hydrocarbons, wax esters, alcohols, and ketones (Tulloch 1976a). The cuticular wax plays an important role in preserving the water balance of the plant by reducing evaporation from the leaf surface. The hydrocarbons together with other waxy components serve as a barrier to the passage of water in and out of the cell, thus preventing water inundation or dehydration (Misra et al. 1984a; Weete et al. 1978). Other protective functions may include minimizing mechanical damage to leaf cells and inhibiting fungal and insect attack. The structural and functional roles of leaf epicuticular waxes along with their biosynthesis and some analytical aspects have been discussed in an excellent review by Eglinton and Hamilton (1967).