Fractionation of Stable Zinc Isotopes in the Zinc Hyperaccumulator Arabidopsis halleri and Nonaccumulator Arabidopsis petraea

Abstract : Zn isotope fractionation may provide new insights into Zn uptake, transport and storage mechanisms in plants. It was investigated here in the Zn hyperaccumulator Arabidopsis halleri and the nonaccumulator A. petraea. Plant growth on hydroponic solution allowed us to measure the isotope fractionation between source Zn (with Zn(2+) as dominant form), shoot and root. Zn isotope mass balance yields mean isotope fractionation between plant and source Zn Delta(66)Zn(in-source) of -0.19 +/- 0.20 parts per thousand in the nonaccumulator and of -0.05 +/- 0.12 parts per thousand in-source in the hyperaccurnulator. The isotope fractionation between shoot Zn and bulk Zn incorporated (Delta(66)Zn(shoot-in)) differs between the nonaccumulator and the hyperaccumulator and is function of root-shoot translocation (as given by mass ratio between shoot Zn and bulk plant Zn). The large isotope fractionation associated with sequestration in the root (0.37 parts per thousand) points to the binding of Zn(2+) with a high affinity ligand in the root cell. We conclude that Zn stable isotopes may help to estimate underground and aerial Zn storage in plants and be useful in studying extracellular and cellular mechanisms of sequestration in the root.