PATHWAYS OF ROOT UPTAKE AND MEMBRANE TRANSPORT OF CD2+ IN THE ZINC/CADMIUM HYPERACCUMULATING PLANT SEDUM PLUMBIZINCICOLA

Uptake and membrane transport of cadmium (Cd) in roots of the hyperaccumulator Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu was characterized by assessing the impact of various inhibitors and ion channel blockers on Cd accumulation as well as the real-time net Cd2+ flux at the roots with application of the scanning ion-selective electrode technique. The uncouplers 2,4-dinitrophenol and P-type adenosine triphosphatase inhibitor Na3VO4 significantly limited Cd2+ uptake and transport kinetics in the root of S. plumbizincicola. These findings indicate that Cd is actively taken up into the roots. The Cd content in plant was significantly decreased with pretreatments of the Ca2+ channel blocker La3+ or Gd3+ and the K+ channel blocker tetraethylammonium, as well as in the presence of higher concentration of Ca2+ and K+. These findings indicated that uptake of Cd2+ into the root of S. plumbizincicola proceeds through ion channels that are permeable to both Ca2+ and K+ as confirmed by the direct evidence of real-time net Cd2+ fluxes at the root surface in the treatments with ion channel inhibitors, as well as in the presence of elevated concentrations of Ca2+ and K+. In addition, the results suggested a role for phytochelatin and protein synthesis in mediating Cd2+ uptake by S. plumbizincicola. These findings increase the understanding of Cd2+ uptake and membrane transport pathways in roots of the Zn/Cd hyperaccumulator S. plumbizincicola. (C) 2016 SETAC