deionised water was added to the pots immediately after the plants
were de-topped to remove all the nutrients from the substrate.
Then, the plants were watered with 500mL of a nutrient solution
identical to that used for cultivation except that KCl was replaced
by 2.5mM RbCl
(Rb+was used as an analogue of K+ to be able to distinguish between the uptake of K+(Rb+) and the discharge of K+(K++Rb+) in the xylem flow during the root exudate collection)