Role of Peroxidase in Lignification of Tobacco Cells

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Abstract
The two peroxidase isoenzyme groups (GI and GIII) localized in the cell walls of tobacco (Nicotiana tabacum L.) tissues were compared with respect to their capacity for NADH-dependent H2O2 formation. Peroxidases of the GIII group are slightly more active than those of the GI group when both are assayed under optimal conditions. This difference is probably not of major regulatory importance. NADH-dependent formation of H2O2 required the presence of Mn2+ and a phenol as cofactors. The addition of H2O2 to the reaction mixture accelerated subsequent NADH-dependent H2O2 formation. In the presence of both cofactors or Mn2+ alone, catalase oxidized NADH. However, if the cofactors were absent or if only dichlorophenol was present, catalase inhibited NADH oxidation. No H2O2 accumulation occurred in the presence of catalase. Superoxide dismutase inhibited NADH oxidation quite significantly indicating the involvement of the superoxide radical in the peroxidase reaction. These results are interpreted to mean that the reactions whereby tobacco cell wall peroxidases catalyze NADH-dependent H2O2 formation are similar to those proposed for horseradish peroxidase (Halliwell 1978 Planta 140: 81-88).

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