Purification and characterization of a neutral peroxidase induced by rubbing tomato internodes

Rubbing applied to a young tomato internode inhibited the elongation of thi s internode and increased soluble peroxidase activity. These morphologic al and biochemical changes Here observed both at the site of rubbing (local r esponse) and in the neighbouring internode (systemic response). The cellula r, biochemical. and molecular mechanisms leading to inhibition of internode elongation are not full! understood. it was proposed that mechanical stimu li increased the oxidation of IAA, via the induction of specific peroxidase s and stimulated the lignification processes. In order to gain more informa tion about the role of these enzymes, analysis of changes in peroxidase act ivities were performed, Qualitative analysis of isoperoxidases, by means of native cathodic PAGE, showed four induced isoforms termed C-1, C-2, C-3, a nd C-4. The major isoform (C-2) was purified to homogeneity and partially c haracterized, This isoform is probably unglycosylated, with a molecular mas s of 36 kDa and a neutral pIof 7.1. The effects of pH and temperature on th e activity Here determined with guaiacol as electron donor. Optima were obt ained at pH 5 and at a temperature of 55 degrees C. The activity of the pur ified enzyme was not affected by Ca2+, Mg2+ and Mn2+ as was reported for so me basic peroxidases. Analysis of substrate specificity revealed that this isoperoxidase acted on ABTS. o-dianisidine, pyrogallol, guaiacol, coniferyl alcohol (monolignol) and IAA but not on syringaldazine. Activity of C-2 is operoxidase on confieryl alcohol and IAA suggests a possible role of peroxi dase C-2 in inhibition of internode elongation, observed in rubbed plants, probably via an increase in lignification processes and regulation of IAA l evels in internode tissues.