Jasmonic acid generation

The alcohol moiety is produced in a different manner from that of the acid moiety. The alcohol moiety resembles the plant hormone jasmonic acid (JA) (26) generated from linolenoyl moiety of lipids via (13,S )-hydroperoxy-linolenic acid (22), (12.13,S )-epoxylinolenic acid (23), and 12-oxo-cis-10.15-phytodienoic acid (24) by the oxylipin or octadecanoid pathway (Fig. 3) [31]. In fact, 13C was incorporated at pyrethrolone (1) carbon positions that agreed with those predicted to be labeled when the alcohol moiety is produced via the pathway (Fig. 3) [30]. Figure 3 illustrates that m-jasmone (25) is hydroxylated to yield jasmololone (4), which is then dehydrogenated to yield pyrethrolone (5). However, it has not yet been determined if this is actually the case. 

Degradation products of LOOHs are able to initiate the production of the ethylene, kinases and G-proteins required to induce an oxidative burst. These events are apparently followed by activation of the genes which encode the generation of jasmonic acid and of salicylic acid. These are in turn able to induce the production of enzymes of the phenylpropanoid pathway [149,150], and enzymes which initiate the biosynthesis of terpenes (e.g. 3-hydroxy-3-methylglutaryl coenzyme A reductase [145,151-153]) and lignins. 

The most well known and well investigated degradation reaction of 13S-HPOTE is the generation of jasmonic acid. 13S-HPOTE is converted by allene oxide hydroperoxydehydrase by an intramolecular elimination of water to an allene oxide [160]. The latter is cyclized by allene oxide cyclase to 9S,13S,12-oxo-10,15-phytodienoic acid [160] followed by a trifold P-oxidation and a hydrogenation step (Scheme 7) [108]. 

Scheme Generation of jasmonic acid as well as a- and y-ketols according to Hamberg [160].

The last route is important for the formation of jasmonic acid. The action of allene oxide synthase on 13-hydroperoxy linolenic acid initially results in the generation of 12,13-epoxy-octadecatrienoic acid. This unstable epoxide is either chemically hydrolyzed to a- and y-ketols and racemic 12-oxo-phytodienoic acid or, in the presence of allene oxide cyclase (AOC), is further converted to enantiomeric pure 12-oxo-PDA [7]. The ring double bond of PDA is then reduced in a NADPH dependent reaction by 12-oxo-PDA reductase and after shortening of the side chain containing the carboxy group by 3 rounds of fi>-oxidation, the biosynthesis of jasmonic acid is completed. 

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