At harvest time, three plants were randomly sampled from each treatment. Samples (500 mg) of leaves
and roots were separately ground to a fine powder in a
mortar under liquid nitrogen. One portion of the powder was suspended in 5 mL of 50 mmol L
−1
potassium phosphate buffer (pH 7.8), homogenized and centrifuged at 14 000×gfor 15 min at 4
◦
C. For chitinase
activity determination, the supernatant was diluted
two times. The colloid chitin was prepared according
to Wu et al. (2009). The chitinase activity was determined based on the method described by Schraudneret al.(1992) using N-acetyl-amino-glucosamine as
standard. One unit of chitinase activity was defined
as the amount of enzyme that produced 1μgofNacetyl-amino-glucosamine per hour from chitin under
these assay conditions. The activity ofβ-1,3-glucanase
was determined using the method of Schraudneret al.
(1992) using laminarine as standard. One unit ofβ-1,
3-glucanase activity was defined as the amount of enzyme that produced 1 nmol reduced sugar per second
under the assay conditions.