13 -hydroperoxylinolenic acid

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Substrate Specificity. Hydroperoxide dehydrase from sunflower cotyledons was about four-fold more active wiA 13-hydroperoxylinoleic acid Aan 13-hydroperoxylinolenic acid. In contrast, leaf hydroperoxide lyase was more Aan 10-fold more active wiA 13-hydroperoxylinolenic acid Aan wiA 13-hydroperoxylinoleic acid. However, root hydroperoxide lyase showed no preference between Ae two substrates, again suggesting Aat roots have a different form of Ae enzyme Aan leaves. NeiAer 9-hydroperoxylinoleic nor 9-hydroperoxylinolenic acids were suitable substrates for any of Ae hydroperoxide metabolizing enzymes in sunflower. 

The initial reaction of the pathway in which a-linolenic acid is converted to 12-oxo-PDA was catalysed with Oj in the presence of soybean lipoxygenase and the resultant hydroperoxide product was 13(S)-hydroperoxylinolenic acid [13(S)-HPOD a minor product was 9-HPOD [30]. A regiospecificity study using partially pure lipoxygenase from V. faba pericarp showed that 92% of the product was 13(S)-HPOD and 8% was the... 

Hamberg, M Sanz, A Gastresana, G. a-Oxidation of fatty acids in higher plants Identification of a pathogen-inducible oxygenase (PIOX) as an a-dioxygenase and biosynthesis of 2-hydroperoxylinolenic acid. J. Biol Chem., 1999, 274, 24503-24513. 

Jasmonic acid is derived from a-linolenic acid, 13(5)-hydroperoxylinolenic acid, 12-oxophytodienoic acid, and phytodienoic acid (Farmer and Ryan, 1990, 1992 Hamberg and Gardner, 1992). The biosynthesis of jasmonic acid and related compounds has been reviewed (Sembdner and Parthier, 1993). 

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