In situ Inactivation of the Oxidase Activity of Xylem Peroxidases by H2O2 in the H2O2-Producing Xylem of Zinnia elegans |
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Authors: | A Ros Barceló |
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Institution: | (1) Department of Plant Biology (Plant Physiology), University of Murcia, E-30100 Murcia, Spain, ES |
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Abstract: | Zinnia elegans stems with 3,3′, 5, 5′-tetramethylbenzidine (TMB) in the presence and in the absence of catalase reveals the presence of
xylem oxidase activities in the H2O2-producing lignifying xylem cells. This staining of lignifying xylem cells with TMB is the result of two independent mechanisms:
one is the catalase-sensitive (H2O2-dependent) peroxidase-mediated oxidation of TMB, and the other the catalase-insensitive (H2O2-independent) oxidation of TMB, probably due to the oxidase activity of xylem peroxidases. The response of this TMB-oxidase
activity of xylem peroxidases to different exogenous H2O2 concentrations was studied, and the results showed that H2O2 at high concentrations (100–1,000 mM) clearly acted as an inactivator of this xylem TMB-oxidase activity, although some inhibitory
effect could still be appreciated at 10 mM H2O2. This xylem TMB-oxidase activity resided in a strongly basic cell wall-bound peroxidase (pl about 10.5). Given such a scenario,
it may be concluded that this TMB-oxidase activity of peroxidase is located in tissues capable of sustaining H2O2 production, and that the in situ oxidase activity shown by this enzyme is inactivated by high H2O2 concentrations.
Received 20 April 1999/ Accepted in revised form 16 August 1999 |
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Keywords: | : Inactivation H2O2 Lignification Xylem oxidases Zinnia elegans |
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