Frozen material was homogenized with cold extraction medium
(4 mL g−1) consisting of 50 mM Hepes-KOH (pH 7), 5 mM MgCl2 and
1 mM EDTA, and analyzed with the Bio-Rad protein assay accord-
ing to Bradford (1976). Pigments were determined in plant extracts
according to Cabello et al. (1998). For H2O2 determination, 1 g
leaf material was ground with 10 mL cool acetone in a cold room
and passed through Whatman filter paper. Hydrogen peroxide was