ABSTRACrSix plant species metabolized SO-labeled 12-oxo-cis,cis-10,15-phytodienoic acid (12-oxo-PDA) to

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12-Oxo-tras-ldodecenoic acid (raas-10-ODA) is an oxidation product of polyuaturated fatty aids in plant tssues. The strutural similarity of tras-10-ODA and traumatic acid, a compound considered to be a wound hormone, suggested that tras-10-ODA might be a precursor of traumatic acid. Both tans-10-ODA and traumatic acid were active in the Wehnelt bean assay. The results were more consistent with tans-10-ODA than with traumatic acid. Cucumber (Cucumis sativus L. var. National Pickling) hypocotyls also showed a growth increase following treatment with trans-10-ODA, which suggested that trans-10-ODA has a more general influence on plant development than previously ascribed to traumatic acid.Runner beans (Phaseolus vulgars L. var. Kentucky Wonder) were analyzed for the presence of endogenous trans-10-ODA and traumatic acid. These are the beans from which traumatic acid was originally isolated in 1939. They contained trans-10-ODA but no traumatic acid. Young beans were a better source of bans-10-ODA than older beans and an increase in the esterified form of trans-10-ODA with age may have been due to a conversion of the free acid to the esterified form. The amount of endogenous trans-10-ODA increased when bean pod tissue was sliced and wounded. Rapid stirring and the presence of oxygen increased autooxidation of trans-10-ODA to traumatic acid in nner beans, which indicated that the compound identified as traumatic acid is formed by autooxidation of trans-10-ODA and that trans-10-ODA is a natural compound with growth-regulating properties.Enzyme extracts of runner beans synthesized trans-10-ODA from inoleic acid. No enzymic synthesis of traumatic acid was observed even when cofactors were added to the reaction mixture. This confirmed the conclusion that traumatic acid is formed by autooxidation of trans-10-ODA. The internodes of Ricinus communis demonstrated a wound response to traumatic acid (18). However, many other tissues have failed to respond to traumatic acid, and Keller (11) and HaagenSmit and Viglierchio (7) reported that crude extracts of beans and citrus fruit were much more active in the Wehnelt assay for wound hormones than was traumatic acid.Vick and Zimmerman (24) recently reported the presence of a hydroperoxide lyase enzyme in watermelon seedlings that converted 13-hydroperoxy-linoleic acid to trans-10-ODA2 and hexanal. Tressl and Drawert (23) proposed that trans-10-ODA was formed from linoleic acid and 13-hydroperoxy-linoleic acid in homogenates of climacteric and postclimacteric bananas. Because of the similarity of the structures, trans-lI-ODA is a possible precursor of traumatic acid via a dehydrogenase. We investigated this possibility by repeating the work of English et al. (4,5) concerning the isolation and physiological activity of traumatic acid.MATERIALS AND METHODS General Conditions. All organic solvents and buffers for enzyme extraction were deoxygenated by bubbling N2 through them for 20 min. Samples were extracted and stored under N2. Enzyme incubations and assays were performed ...

Lipoxygenase (EC 1.13.1.13) was found in seedlings of Citrullus lanatus (Thunb.) Matsum. and Nakai (watermelon). The enzyme has pH optima of 4.4 and 5.5 and is inhibited by 0.2 mM nordihydroguaiaretic acid. It is present in two functional units with estimated molecular weights of 120,000 and 240,000, respectively.A new enzyme, tentatively termed hydroperoxide lyase, has been partially purified from watermelon seedlings. The enzyme, located principally in the region of the hypocotyl-root junction, catalyzes the conversion of 13-l-hydroperoxy-cis-9-trans-11-octadecadienoic acid to 12-oxo-trans-10-dodecenoic acid and hexanal. The hydroperoxide lyase enzyme from watermelon has a molecular weight in excess of 250,000, a pH optimum in the range of 6 to 6.5, and is inhibited by p-chloromercuribenzoic acid. Its presence has also been demonstrated in other cucurbits.The maximum activity of both enzymes occurs on the 6th day of germination. The identification of the products of the hydroperoxide lyase reaction suggests that lipoxygenase and hydroperoxide lyase may be involved in the conversion of certain polyunsaturated fatty acids to traumatic acid (trans-2-dodecenedioic acid).