Effects of cadmium and copper on peroxidase, NADH oxidase and IAA oxidase activities in cell wall, soluble and microsomal membrane fractions of pea roots

Twelve-day-old seedlings of pea (Pisum sativum L.) that were treated for 4 days by 20 and 100 mumol/l Cd(NO3)(2) or CuSO4 showed a growth reduction in all organs. From root protein extracts, the activities of guaiacol peroxidase (GPX; EC 1.11.1.7), ascorbate peroxidase (APX; EC 1.11.1.11), coniferyl alcohol, peroxidase (CAPX), NADH oxidase, and indole-3-acetic acid (IAA) oxidase were measured in covalently-and ionically-circle minus bound cell wall, soluble, and microsomal membrane fractions. With the exception of 20 mumol/l Cu, metal treatments enhanced GPX activity in all fractions. Only IAA oxidase activity was metal-elevated in the covalently bound cell wall fraction, white the ionic one showed Cd stimulation for all, assayed enzymic activities. These effects were not entirety observed in Cu-treated plants, since APX and IAA oxidase activities were only enhanced in this fraction. However, soluble extract showed stimulation of APX activity, while in the microsomal fraction metal exposure also increased the activities of CAPX and NADH oxidase. Differential responses of root cell fractions to the presence of cadmium and copper ions are discussed in regard to the contribution of their enzymic capacities in antioxidant, lignification, and auxin degradation pathways. Comparisons between metals and dose effects are also underlined. (C) 2004 Elsevier GrnbH. All rights reserved.