Phloem-specific transporter OsLCT1 at nodes regulates preferential Cd transport to upper nodes and grains

Uraguchi, Shimpei*; Suzui, Nobuo; Yin, Y.-G.; Ishii, Satomi; Fujimaki, Shu; Fujiwara, Toru*

We have previously reported that encodes a Cd transporter on plasma membrane and regulates grain Cd accumulation in rice. strongly expresses in both leaf blades and nodes during reproductive stages. This raises a possibility that OsLCT1 is involved in Cd translocation from leaf to grains and/or is involved in intervascular Cd transport at nodes. In this study, we clarified the contribution of OsLCT1 in Cd transport into grains by serial isotopic analyses. The experiment using two different stable isotope of Cd showed that knock-down and knock-out of decreased the direct Cd transport from roots to grain through nodes but did not affect Cd translocation from leaf blades. The live-imaging analysis using positron emitting radioisotope Cd demonstrated that Cd absorbed by roots was preferentially transported to upper nodes rather than to leaf blades and knock-down of retarded the Cd transport into upper nodes. The improved method for collecting phloem sap using plant brown hopper was established and the Cd level in phloem sap collected from a panicle neck was significantly lower in two different knock-down lines. Immunostaining confirmed the phloem specific expression of OsLCT1 in large vascular bundles and diffuse vascular bundles. These results suggest that OsLCT1 is involved in re-direction of Cd to upper nodes (and a panicle) at nodes probably facilitating Cd loading into sieve element.