Pathways of cadmium fluxes in the root of the hyperaccumulator Celosia argentea Linn.

Abstract

In order to study the mechanism of cadmium (Cd) uptake by the roots of Celosia argentea Linn. (Amaranthaceae), the effects of various inhibitors, ion channel blockers, and hydroponic conditions on Cd2+ fluxes in the roots were characterized using non-invasive micro-test technology (NMT). The net Cd2+ flux (72.5pmol∙cm-2∙s-1) in roots that had been pretreated with Mn was significantly higher than that in non-pretreated roots (58.1pmol∙cm-2∙s-1), indicating that Mn pretreatment enhanced Cd uptake by the roots. This finding may be explained by the fact that the addition of Mn significantly increased the expression of the transporter gene and thus promoted Cd uptake and transport. In addition, Mn pretreatment resulted in an increase in root growth, which may in turn promote root vigor. The uncoupler 2,4-dinitrophenol (DNP) caused a significant reduction in net Cd2+ fluxes in the roots, by 70.5% and 41.4% when exposed to Mn and Cd stress, respectively. In contrast, a P-type ATPase inhibitor (Na3VO4) had only a small effect on net Cd2+ fluxes to the plant roots, indicating that ATP has a relatively minor role in Cd uptake by roots. La3+ (a Ca channel inhibitor) had a more significant inhibitory effect on net Cd2+ fluxes than did TEA (a K channel inhibitor). Therefore, Cd uptake by plant roots may occur mainly through Ca channels rather than K channels. In summary, uptake of Cd by the roots of C. argentea appears to occur via several types of ion channels, and Mn can promote Cd uptake.