The enzyme, characterized from the endosperm of the plant Thunbergia alata (black-eyed Susan vine), introduces a cis double bond at carbon 6 of several saturated acyl-[acyl-carrier protein]s. It is most active with palmitoyl-[acyl-carrier protein] (16:0), but can also act on myristoyl-[acyl-carrier protein] (14:0) and stearoyl-[acyl-carrier protein] (18:0). The position of the double bond is determined by its distance from the carboxyl end of the fatty acid.