Because of their biochemical importance and relative ease of study, the waxes of the plant cuticle
have received most study. All the aliphatic components of plant waxes are synthesised in the
epidermal cells from saturated very-long-chain fatty acids (commonly C20 to C34). 16:0 and 18:0
fatty acids are first synthesised in the stroma of plastids by the soluble enzymes forming the fatty
acid synthase complex (see our web page on fatty acid biosynthesis). The second stage
involves multiple elongation steps and is catalysed by membrane-associated multi-enzyme
complexes, known as fatty acid elongases, outwith the plastids. As in fatty acid synthesis de novo,
each two-carbon extension of the chain involves four reactions: condensation between a CoAesterified
fatty acyl substrate and malonyl-CoA, followed by a β-keto reduction, dehydration and an
enoyl reduction to produce saturated very-long-chain fatty acids with 24 to 36 carbon atoms. Manydifferent forms of the elongases have been identified, and these must interact in some manner to
produce the chain-length specificity observed.