Formation of manganese oxide plaque on rice roots in solution culture under varying pH and manganese (Mn2+) concentration conditions

Abstract

Abstract Roots of rice (Oryza sativa L.) exposed to 25, 50, and 100 ppm concentrations of manganese (Mn2+) in solution culture at pH 4.0, 5.0, 6.0, 7.0, and 8.0 for 48 hours developed visible brown coatings (plaque) of oxidized Mn. Most plaque was deposited on a region of the root 1–6 cm long above the root tip. Manganese in root plaque was removed by dithionite‐bicarbonate‐citrate extraction and internal root Mn released by pressure digestion. Concentrations of Mn were determined by atomic absorption spectrometry. Mean concentrations of Mn in plaque exceeded concentrations of Mn remaining in roots after the DCB wash in all treatment conditions. Concentrations of plaque and internal Mn increased with increasing pH and Mn2+ concentration in the treatment solution. Significant positive correlations existed between plaque and internal Mn concentrations at high pH. A larger percentage of total root metal remains in Mn plaqued roots after DCB treatment than has been previously observed in similarly treated iron (Fe) plaqued roots.