Peroxidases in the cell walls of seeds and seedlings of Araucaria araucana

Abstract

Two major proteins present in the cell walls of the embryo and megagametophyte tissues of Araucaria araucana seeds were partially purified, characterized and identified as peroxidases. These two proteins have Mrs of 83 and 145 × 103, a pI of 10.5, an optimal pH of 5.0 and a buoyant density of 1.333 g ml−1. Kinetic studies of these peroxidases define a Km app. of 13.6 mM for H2O2 and 3.4 mM for o-phenylenediamine (o-PDA). The Vmax is 525 μmol o-PDA oxidized min−1 mg−1. After oxidation with periodic acid the peroxidases react on gels with dansylhydrazine, demonstrating that the proteins are glycosylated. The sugar components linked to the proteins are galactose, glucose, xylose and mannose. Galactose comprises more than 60% of the sugar residues in both peroxidases. The other sugar contents show significant quantitative differences between the peroxidases. Expression of the peroxidases increases upon wounding of the seed tissues. The two proteins were differently expressed during seed germination. They also showed a different susceptibility to degradation when the proteins were heated in the presence of 5 M urea.