Polysaccharide degradation by Fenton reaction- or peroxidase-generated hydroxyl radicals in isolated plant cell walls

The formation of hydroxyl radicals (OH.) by peroxidase was confirmed by EPR spectroscopy using ethanol/alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone as a spin-trapping system specific of OH.. The effect of OH., generated either non-enzymatically with the Fenton reaction (H2O2 + Fe2+) or with horseradish peroxidase in the presence of O-2 and NADH, on cell walls isolated from maize (Zea mays) coleoptiles or soybean (Glycine max) hypocotyls was investigated. OH. produced by these reactions attack polysaccharides in the wall, demonstrated by the release of a heterogeneous mixture of polymeric breakdown products into the incubation medium. The peroxidase-catalyzed degradation of cell-wall polysaccharides can be inhibited by KCN and superoxide radical (O-2(.-)) or OH. scavengers. These data support the hypothesis that OH., produced by cell-wall peroxidases in vivo, act as wall-loosening agents in plant extension growth. (C) 2002 Elsevier Science Ltd. All rights reserved.