Lateral Roots but Not Root Hairs Contribute to High Uptake of Manganese and Cadmium in Rice

Rice (Oryza sativa L.) can accumulate high manganese (Mn) in the shoots through uptake by the roots, which consist of crown roots, lateral roots and root hairs. We investigated the role of lateral roots and root hairs in Mn and cadmium (Cd) uptake by using two indica rice mutants defective in formation of lateral roots (osiaa11) and root hairs (osrhl1). The uptake of Mn and Cd in osiaa11 was significantly lower than that in wild type 'Kasalath', but there was no difference between wild type and osrhl1. Furthermore, a kinetic study showed that Mn uptake in osiaa11 was much lower than that in wild type and osrhl1 across a wide range of Mn concentrations. The role of lateral roots in Mn and Cd uptake was further confirmed in a japonica rice mutant defective in lateral root formation. We found that expression of Mn transporter gene Natural Resistance-Associated Macrophage Protein 5 (OsNRAMP5), but not of Metal Tolerance Protein 9 (OsMTP9), was lower in osiaa11 than in wild type; however, there were no differences between osrhl1 and the wild type. Immunostaining showed that OsNRAMP5 and OsMTP9 were localized in the exodermis and endodermis of crown roots and lateral roots, but not in the root hairs. Taken together, our results indicate that lateral roots, but not root hairs, play an important role in high Mn and Cd uptake in rice.