Root length and shoot height were measured
manually with a ruler and dry weights of shoot and
root were determined after drying at 80 °C for 24 h.
Relative electrolyte leakage as a measurement for
membrane permeability was determined according to
the method of Li (2001). Leaves of seedlings were cut
into segments of about 5 mm. Each replication (0.2 g
fresh weight (FW)) was collected and washed with
deionized water, and then placed in the test tube with
10 ml deionized water and covered with a plug. After
incubation at 25 °C for 6 h, the relative electrolyte
leakage of the leaves was measured using a conductometer
(DDS-11A, Shanghai, China), and the value
was named E1. Subsequently, the test tube was kept in
water at 100 °C for 30 min, and then cooled to 25 °C,
and the second relative electrolyte leakage was
measured as E2. The relative electrolyte leakage of
deionized water was named E0. The relative electrolyte
leakage (REL) was calculated as follows: REL
(%)=(E1−E0)/(E2−E0)×100. The concentrations of
malondialdehyde (MDA), proline, and soluble sugar
in leaves were measured using thiobarbituric acid
(TBA) reaction method, colorimetric method, and
anthrone colorimetric method, respectively (Li, 2001).
Leaf peroxidase (POD) activity was determined by
guaiacol method (Zhu and Zhong, 1990), and leaf
catalase (CAT) activity was determined by the
method described by Fu and Huang (2001). All
measurements mentioned above were made after seed
germination for 8 d (at 25 °C under alternating cycle
of 12 h illumination and 12 h darkness for 5 d, followed
by low temperature stress at 5 °C for 3 d) on 20
randomly selected seedlings per measurement