The measurement of the root acidification capacity followed the
method described by Zocchi and Cocucci (1990). The preincubation
was carried out for 60 min, at pH 6.2, using 8 g of excised
roots, in a shaking bath (100 oscillations/min) maintained at 26·C.
The ATPase proton pump activity was thereafter measured using a
Radiometer 64 pH-meter.
Electrolytic conductance was determined with a Crison 522 conductimeter,
according to Ketchie (1969). Three grams of roots and
shoots were incubated with deionized water for 8 h; thereafter, the
absolute conductance Was measured. After a heat shock treatment at
100 ·C for 7 min, the volume of deionized water was corrected and