The pathway of transmembrane cadmium influx via calcium-permeable channels and its spatial characteristics along rice root

To develop elite crops with low cadmium (Cd), a fundamental understanding of the mechanism of Cd uptake by crop roots is necessary. Here, a new mechanism for Cd(2+) entry into rice root cells was investigated. The results showed that Cd(2+) influx in rice roots exhibited spatially and temporally dynamic patterns. There was a clear longitudinal variation in Cd uptake along rice roots, with the root tip showing much higher Cd(2+) influx and concentration than the root mature zone, which might be due to the much higher expression of the well-known Cd transporter genes OsIRT1, OsNRAMP1, OsNRAMP5, and OsZIP1 in the root tip. Both the net Cd(2+) influx and the uptake of Cd in rice roots were highly inhibited by ion channel blockers Gd(3+) and TEA(+), supplementation of Ca(2+) and K(+), and the plasma membrane H(+)-ATPase inhibitor vanadate, with Gd(3+) and Ca(2+) showing the most inhibitory effects. Furthermore, Ca(2+)- or Gd(3+)-induced reduction in Cd(2+) influx and Cd uptake did not coincide with the expression of Cd transporter genes, but with that of two Ca channel genes, OsAAN4 and OsGLR3.4. These results indicate that Cd transporters are in part responsible for Cd(2+) entry into rice root, and provide a new perspective that the Ca channels OsAAN4 and OsGLR3.4 might play an important role in rice root Cd uptake.