BIOLOGICAL ROLES AND BIOCHEMISTRY OF THE LIPOXYGENASE PATHWAY

Abstract

Two branches of the lipoxygenase pathway seem to universally predominate in plants. One such pathway involves chain-cleavage of fatty acid hydroperoxides into aldehydes, and another is chain cyclization of a linolenic hydroperoxide with eventual transformation into jasmonates. The aldehyde pathway, which furnishes green-grassy or cucumber-like odors, is triggered by wounding or pathogen attack. The aldehydes generated are defensive against the growth of pathogenic bacteria/fungi. Recently, the aldehyde pathway has been extended to include the transformation of cis-3-hexenal and cis-3-nonenal into 4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal, respectively, the latter of which are cytotoxic. The other pathway leads to the biosynthesis of the jasmonate phytohormones. The initial biosynthetic product, 7-isojasmonic acid, becomes converted into jasmonic acid, as well as a large family of related compounds. The jasmonates control diverse physiological processes, such as induction of proteins, defensive enzymes, tuberization, secondary metabolites, and senescence.