It is further dehydrated to an unstable allene oxide by AOS, and then can be hydrolyzed to α- or g-ketols, or racemic oxophytodienoic acid (OPDA).In the presence of allene oxide cyclase (AOC), only the cis-(+)-enantiomer (9S, 13S) of OPDA is formed, which is thought to be the precursor of JA (Vick and Zimmerman 1983), indicating a crucial role of AOC in
jasmonate biosynthesis.