The enzymes from the plants Dimorphotheca sinuata (African daisy) and Vernicia fordii (tung oil tree) insert a trans double bond in position C-12 of oleate and palmitoleate incorporated into glycerolipids. The enzyme introduces the new double bond at a position three carbons away from an existing double bond at position 9, towards the methyl end of the fatty acid. The enzyme from tung oil tree also possesses the activity of EC 1.14.19.33, ¦¤12 acyl-lipid conjugase.