HMA P-type ATPases are the major mechanism for root-to-shoot Cd translocation in Arabidopsis thaliana

The Zn/Cd-transporting ATPases, HMA2 and HMA4, essential for root-to-shoot Zn translocation, are also able to transport Cd. Phytochelatins ( PCs) are a major mechanism of Cd detoxification through the sequestration of PC-Cd complexes in vacuoles. The roles of HMA2 and HMA4 in root-to-shoot Cd translocation and Cd tolerance were investigated in the PC-deficient, cad1-3 mutant and CAD1 backgrounds. Six lines, with all possible combinations of hma2, hma4 and cad1 mutations, were constructed. The lines were tested for Cd-sensitivity on agar medium, and radioactive 109Cd was used to measure Cd uptake and translocation from root to shoot over periods of up to 6d. In hma4 and hma2, hma4, but not hma2, root-to-shoot Cd translocation was decreased to about 60 and 2%, respectively, of that in the wild-type. Cd sensitivity increased approximately twofold in the hma2, hma4 mutant in both CAD1 and cad1 backgrounds. PC deficiency resulted in an increase in shoot Cd concentrations. The near-complete abolition of root-to-shoot Cd translocation resulting from the loss of function of HMA2 and HMA4 demonstrates they are the major mechanism for Cd translocation in Arabidopsis thaliana.