Catalyzes the desaturation of oleic acid to linoleic acid. Introduces a double bond at position 12 of 16:1(9Z) and 18:1(9Z). Lipid metabolism; polyunsaturated fatty acid biosynthesis. Expressed in leaves, flower buds and developing seeds. The histidine box domains may contain the active site and/or be involved in metal ion binding. Belongs to the fatty acid desaturase type 1 family.