THE OCTADECANOIC PATHWAY - SIGNAL MOLECULES FOR THE REGULATION OF SECONDARY PATHWAYS

Plant defense against microbial pathogens and herbivores relies heavil y on the induction of defense proteins and low molecular weight antibi otics, The signals between perception of the aggression, gene activati on, and the subsequent biosynthesis of secondary compounds are assumed to be pentacylic oxylipin derivatives. The rapid, but transient, synt hesis of cis-jasmonic acid was demonstrated after insect attack on a f ood plant and by microbial elicitor addition to plant suspension cultu res. This effect is highly specific and not caused by a number of envi ronmental stresses such as light, heavy metals, or cold or heat shock. Elicitation of Eschscholtzia cell cultures also led to a rapid alkali nization of the growth medium prior to jasmonate formation, Inhibition of this alkalinization process by the protein kinase inhibitor stauro sporine also inhibited jasmonate formation. The induction of specific enzymes in the benzo[c]phenanthridine alkaloid pathway leading to the antimicrobial sanguinarine was induced to a qualitatively and quantita tively similar extent by fungal elicitor, methyl jasmonate, and its li nolenic acid-derived precursor 12-oxophytodienoic acid. It is herein p roposed that a second oxylipid cascade may exist in plants starting fr om linoleic acid via 15,16-dihydro-12-oxophytodienoic acid to 9,10-dih ydrojasmonate. Experiments with synthetic trihomojasmonate demonstrate d that beta-oxidation is not a prerequisite for biological activity an d that 12-oxophytodienoic acid and derivatives are most likely fully a ctive as signal transducers. Octadecanoic acid-derived compounds are e ssential elements in modulating the synthesis of antibiotic compounds and are thus integral to plant defense.