characterization and cdnamicroarray expression analysis of 12oxophytodienoate reductases reveals differential roles for octadecanoid biosynthesis in the local versus the systemic wound response 12oxophytodienoate reductases oprs belong to a family of flavindependent oxidoreductases with two new tomato isoforms reported here three oprs have now been characterized in both tomato and arabidopsis only one of these isoforms opr3 participates directly in the octadecanoid pathway for jasmonic acid biosynthesis as only opr3 reduces the 9s13sstereoisomer of 12oxophytodienoic acid the biological precursor of jasmonic acid the subcellular localization of oprs was analyzed in tomato and arabidopsis the opr3 protein and activity were consistently found in peroxisomes where they colocalize with the enzymes of betaoxidation which catalyze the final steps in the formation of jasmonic acid the octadecanoid pathway is thus confined to plastids and peroxisomes and in contrast to previous assumptions does not involve the cytosolic compartment the expression of tomato lycopersicon esculentumle opr3 was analyzed in the context of defenserelated genes using a microarray comprising 233 cdna probes leopr3 was found to be upregulated after wounding with induction kinetics resembling those of other octadecanoid pathway enzymes in contrast to the induction of genes for wound response proteins eg proteinase inhibitors the accumulation of octadecanoid pathway transcripts was found to be more rapid and transient in wounded leaves but hardly detectable in unwounded systemic leaves consistent with the expression data opda and ja were found to accumulate locally but not systemically in the leaves of wounded tomato plants the transcriptional activation of the octadecanoid pathway and the accumulation of ja to high levels are thus not required for the activation of defense gene expression in systemic tissues