For determination of catalase and APX, enzyme extracts were
prepared by freezing the weighed amount of leaf samples in liq-
uid nitrogen to prevent proteolytic activity, which was followed
by grinding in 0.1 M phosphate buffer at pH 7.5 containing 0.5 mM
EDTA and 1 mM ascorbic acid in a 1:10 (w/v) ratio. The homogenate
was passed through four layers of gauze and the filtrate centrifuged
at 15,000 × g for 20 min, and the resulting supernatant was used as
enzyme source.