Biosynthesis of new divinyl ether oxylipins in Ranunculus plants

[1-14C]Linolenic acid was incubated with homogenates of leaves from the aquatic plants Ranunculus lingua (greater spearwort) or R. peltatus (pond water-crowfoot). Analysis by reversed-phase high-performance liquid radiochromatography demonstrated the formation of a new divinyl ether FA, i.e., 12-[1'(E),3'(Z)-hexadienyloxyl-9(Z), 11 (Z)-dodecadienoic acid [11 (Z)-etherolenic acid] as well as a smaller proportion of omega5(Z)-etherolenic acid previously identified in terrestrial Ranunculus plants. The same divinyl ethers were formed upon incubation of 13(S)-hydroperoxy-9(Z),11 (E),15(Z)-octadecatrienoic acid, a lipoxygenase metabolite of linolenic acid, whereas the isomeric hydroperoxide, 9(S)-hydroperoxy-10(E),12(Z),15(Z)-octadecatrienoic acid, was not converted into divinyl ethers in R. lingua or R. peltatus. Incubation of [1-14C]linoleic acid or 13(S)-hydroperoxy-9(Z), 11 (E)-octadecadienoic acid produced the divinyl ether 12-[1'(E)-hexenyloxyl-9(Z),11(Z)-dodecadienoic acid [11(Z)-etheroleic acid] and a smaller amount of omega5(Z)-etheroleic acid. The experiments demonstrated the existence in R. lingua and R. peltatus of a divinyl ether synthase distinct from those previously encountered in higher plants and algae.