Oxylipin biosynthesis. Oxylipin biosynthesis starts with the release of α-linolenic acid (α-LeA) from chloroplast membranes . This fatty acid can be metabolized by the action of 13-lipoxygenase (13-LOX) that leads to (13S)-hydroperoxyoctadecatrienoic acid (13-HPOT). The first step in jasmonic acid (JA) biosynthesis is carried out by an allene oxide synthase (AOS) leading to an unstable allene oxide. This intermediate is converted by an allene oxide cyclase (AOC) into (9S,13S)-12-oxo phytodienoic acid (OPDA). The subsequent step, reduction of the cyclopentenone ring, is catalysed by an OPDA reductase (OPR). Three rounds of β-oxidative side-chain shortening starting with 3-oxo-2-(pent-2'-enyl)-cyclopentane-1-octanoic acid (OPC-8) via 3-oxo-2-(pent-2'-enyl)-cyclopentane-1-hexanoic acid (OPC-6) and 3-oxo-2-(pent-2'-enyl)-cyclopentane-1-butanoic acid (OPC-4) lead to the synthesis of JA. Beside the JA biosynthesis pathway, the LOX-product 13-HPOT can be either reduced to (13S)-hydroxyoctadecatrienoic acid (13-HOT) or under certain conditions, such as low oxygen pressure to 13-ketooctadecatrienoic acid (13-KOT) by the action of 13-LOX. The mutation of the AOS gene of the dde 2–2 mutant leads to a deficiency in the JA biosynthesis .