Allene Oxide Synthase Pathway in Cereal Roots: Detection of Novel Oxylipin Graminoxins

Young roots of wheat, barley, and sorghum, as well as methyl jasmonate pretreated rice seedlings, undergo an unprecedented allene oxide synthase pathway targeted to previously unknown oxylipins 1–3. These Favorskii‐type products, (4Z)‐2‐pentyl‐4‐tridecene‐1,13‐dioic acid (1), (2′Z)‐2‐(2′‐octenyl)‐decane‐1,10‐dioic acid (2), and (2′Z,5′Z)‐2‐(2′,5′‐octadienyl)‐decane‐1,10‐dioic acid (3), have a carboxy function at the side chain, as revealed by their MS and NMR spectral data. Compounds 1–3 were the major oxylipins detected, along with the related α‐ketols. Products 1–3 were biosynthesized from (9Z,11E,13S)‐13‐hydroperoxy‐9,11‐octadecadienoic acid, (9S,10E,12Z)‐9‐hydroperoxy‐10,12‐octadecadienoic acid (9‐HPOD), and (9S,10E,12Z,15Z)‐9‐hydroperoxy‐10,12,15‐octadecatrienoic acid, respectively, via the corresponding allene oxides and cyclopropanones. The data indicate that conversion of the allene oxide into the cyclopropanone is controlled by soluble cyclase. The short‐lived cyclopropanones are hydrolyzed to products 1–3. The collective name “graminoxins” has been ascribed to oxylipins 1–3.