The root activity was determined using the a-naphtylamine
oxidation process (Zhang and Qu, 2001). The oxidated amount of
a-naphtylamine (in mg g1FW h1) was determined for per hour and
per fresh root. About 0.1 g of the root, including root tips and root hair
zone, were sampled and homogenized in 5 mL of 50 mg L1
a-naphtylamine and 5 mL of phosphate buffer at pH 7. The homogenized
mixture was shaken gently and placed in the thermo-tank for
24 h. Four solutions, 2 mL of a-naphtylamine solution, 10 mL of
distilled water,1mL of 1% p-aminobenzene sulfonic acid and 1mL of
sodiumnitrite,were addedtothemixturewiththe total volume of the
mixed solution at 25 mL and then kept at room temperature. The
amount ofa-naphtylaminewasdeterminedfromthe absorbance data
at 510 nm