Measurement of ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities
A leaf blade was homogenized by the enzyme extract solution [50 mM potassium phosphate buffer (pH 7.0), 1 mM EDTA, 20% (w/v) sorbitol, 5% (w/v) polyvinylpyrrolidone, 1% (w/v) Tween-20, and 1 mM ascorbate] with quartz sand. The APX activities were measured by following Amako et al. (1994). The SOD activities were measured according to Flóhe & Ötting (1984).