Plant waxes

The surface of plants is covered with a complex mixture of lipids, often in crystalline form, called plant waxes. The chemistry, biosynthesis, catabolism and function of plant waxes are reviewed. The most common components are hydrocarbons, wax esters, free fatty alcohols and acids. Ketones, secondary alcohols, diols, aldehydes, terpenes and flavones are also found. The major function of the wax appears to be protection of the organism from water loss and other hazards of the environment. The alkanes are formed from fatty acids either by elongation followed by decarboxylation or by head‐to‐head condensation between two biochemically dissimilar fatty acids followed by specific decarboxylation of one of them. Fatty acyl‐CoA is reduced to the aldehyde which in turn is reduced to the alcohol. The alcohol is then esterified with acyl moieties from acyl‐CoA or phospholipids. Plant waxes undergo very little catabolism in plants but animals can degrade them to a limited extent and microorganisms readily degrade them.