Homogenates used to determine enzyme activity were prepared as described (Eastmond et al., 2000). Cell-free preparations were obtained from 6-week-old rosette leaves . Leaves (200 mg) were washed, frozen under liquid nitrogen, and ground to a powder. The powdered material was homogenized with 600 mL of buffer containing 50 mM Tris-HCl, pH 8.0, 5 mM EDTA, 1 mM phenylmethylsulfonyl fluoride, and 40 mM 2-mercaptoethanol. The homogenate was centrifuged at 12,000 g for 20 m in at 4℃, and the supernatant was collected.