Extracts for measuring enzyme activities were made by grinding
approximately 100mg FW of root tip material (or 3 leaf disks,
0.96cm2 each) in a mortar with 1mL of extraction buffer containing
30mMsorbitol, 1% BSA and 1% PVP in 100mMHEPES–KOH, pH
8.0. The slurry was centrifuged for 15min at 10,000×g and 4 ◦C,
and the supernatant was collected and analysed immediately.