After a stabilization period of 4h, the exudates from the xylem vessels were collected in testtubes overa 6-h period (4th to10th h fromthe onset of exudation). During this period, the roots were maintained inthesame flasks in which the plants were grown,andtheexternal
medium was continuously aerated and maintained at 25C. Then,
the roots were individually washed in 150mL of cold 5mM CaSO
4solution (5C) for 5min to allow the exchange of the cell wall
contents. Finally, the shoot, roots and their exuded sap were
individually weighed, frozen and stored at20
C.