Induction of Nickel Accumulation in Response to Zinc Deficiency in Arabidopsis thaliana

Excessive accumulation of nickel (Ni) can be toxic to plants. In Arabidopsis thaliana, the Fe(2+) transporter, iron (Fe)-regulated transporter1 (IRT1), mediates Fe uptake and also implicates in Ni(2+) uptake at roots; however, the underlying mechanism of Ni(2+) uptake and accumulation remains unelucidated. In the present study, we found that zinc (Zn) deficient conditions resulted in increased accumulation of Ni in plants, particularly in roots, in A. thaliana. In order to elucidate the underlying mechanisms of Ni uptake correlating zinc condition, we traced (63)Ni isotope in response to Zn and found that (i) Zn deficiency induces short-term Ni(2+) absorption and (ii) Zn(2+) inhibits Ni(2+) uptake, suggesting competitive uptake between Ni and Zn. Furthermore, the Zrt/Irt-like protein 3 (ZIP3)-defective mutant with an elevated Zn-deficient response exhibited higher Ni accumulation than the wild type, further supporting that the response to Zn deficiency induces Ni accumulation. Previously, expression profile study demonstrated that IRT1 expression is not inducible by Zn deficiency. In the present study, we found increased Ni accumulation in IRT1-null mutant under Zn deficiency in agar culture. These suggest that Zn deficiency induces Ni accumulation in an IRT1-independen manner. The present study revealed that Ni accumulation is inducible in response to Zn deficiency, which may be attributable to a Zn uptake transporter induced by Zn deficiency.