Nitrite in the Root Zone Increases The Peroxidase Activity of Wheat Roots at pH 4.0

Abstract

Nitrate is the principal source of nitrogen in soil, but nitrite may also accumulate in the root zone under environmental stress conditions. Nitrite ion is an additional potential N source for wheat plants, but it proved to be a stress factor below pH 4.5. 1 mM nitrite nutrition reduced the elongation and dry matter accumulation of wheat roots at pH 4.0 as compared with those of plants growing in a culture solution containing 1 mM nitrate, but did not inhibit these parameters at pH 7.0. The activities of soluble and cell wall-bound peroxidase fractions of roots with guaiacol as substrate were increased significantly in all culture media at pH 4.0 as compared with those of plants growing at pH 7.0, but the effect of nitrite was much greater in the peroxidase fractions bound ionically or covalently to the cell wall. The changes in peroxidase activities coincide well with the significant inhibition of root elongation by nitrite nutrition at pH 4.0. The cell wall-bound isoenzymes of peroxidases may regulate the elongation growth of roots by decreasing the plasticity of the cell walls.