ENZYMES OF OCTADECANOID BIOSYNTHESIS IN PLANTS - 12-OXO-PHYTODIENOATE10,11-REDUCTASE

Octadecanoids, potent cyclic plant signaling molecules derived from al pha-linolenic acid, are involved in the regulation of a multitude of p hysiological processes such as senescence, herbivore and pathogen defe nse, mechanoperception and morphogenesis. The first cyclic intermediat e in the Vick-Zimmerman pathway of octadecanoid biosynthesis is 12-oxo -phytodienoic acid. Its conversion to the end product of the pathway, jasmonic acid, a C-12 compound, first proceeds through reduction to 3- oxo-2-(pent-2'-enyl)-cyclopentane-1-octanoic acid, which is then conve rted to jasmonic acid by three cycles of beta-oxidation. The first of these conversions is a decisive point in the biosynthetic sequence, in that it channels the octadecanoid into the pathway of beta-oxidation. 12-Oxo-phytodienoate reductase was purified to apparent homogeneity f rom a cell suspension culture of Corydalis sempervirens. The enzyme is soluble and a monomer of apparent molecular mass 41 kDa which prefers NADPH over NADK to reduce the 10,11-double bond of 12-oxo-phytodienoi c acid. The structure of the reaction product was proved by derivatiza tion, GC/MS and NMR analysis. The enzyme accepts both the cis and the trans isomer of 12-oxophydodienoic acid, with a preference for the cis -isomer (6:1). 12-Oxo-phytodienoate reductase will also convert the sy nthetic substrate 2-cyclohexenone to cyclohexanone, but the enzyme did not reduce some other cyclic alpha,beta-unsaturated ketones tested (t he plant hormone abscisic acid or the steroids testosterone and proges terone). Characteristic parameters of 12-oxo-phytodienoate reductase w ere determined.