2.5 Measurement of citrate in root exudates
The citrate concentration of root exudate from excised root tips of
XZ29, XZ9 and Dayton was determined according to Wang et al (2007).
Briefly, twenty 10-mm root tips of two-day-old seedlings were excised
and washed for three times with 1 ml of control solution (200 μM
CaCl2, pH 4.3). Treatment solutions (200 μM
CaCl2, pH 4.3,
with
or without 5 μM AlCl3) were added and the tubes
containing the root tips were incubated at 60 rpm for 2 h using a
platform shaker. Then the solution was collected for citrate measurement
according to Wang et al. (2007).