Unusual Fatty Acids

This chapter provides an overview of the major questions concerning unusual fatty acid biosynthesis. It presents an overview of certain aspects of contemporary enzymology which are relevant to the important class of enzymes, such as desaturases and hydroxylases, which participate in 0₂-dependent modifications of fatty acids. A feature of unusual fatty acids is that they are generally confined to seed triacylglycerols. Analyses of vegetative tissues have generated few reports of unusual fatty acids, other than those occurring in the cuticle. Since the ability to synthesize various unusual fatty acids must have evolved independently, the common feature of confinement to seed triacylglycerol indicates some selective constraint or functional significance. One possible function of unusual fatty acids is that by being toxic or indigestible they protect the seed against herbivory. Desaturation of plant fatty acids at the Δ⁶ position seems to occur by two unrelated pathways. One pathway is widespread in seeds of the Apiaceae, Araliaceae, and Garryaceae which accumulate petroselinic acid.