| Summary: | Using plants as bioremediation agents are rising worldwide as an environmentally friendly tool to remove contaminants such as heavy metals. Arabidopsis halleri ssp. gemmifera is able to hyperaccumulate Cd/Zn, however, the commonality between Cd/Zn accumulation pathways are still vague. This study focused on HMA4 and IRT3 as indicators and investigated their transcription in A. halleri ssp. gemmifera under Cd/Zn treatments. In addition to the known Cd/Zn xylem loading functions in roots, HMA4 showed a potential role in Cd/Zn redistribution or metal efflux from the vascular bundle in leaves due to increased transcription by 3-fold after 7 d under all treatments. On the other hand, IRT3 as a Zn homeostasis gene was expressed continuously in both roots and leaves under single Cd or Zn treatment. However, IRT3 transcription in leaves plunged to 50-fold lower under combined Cd and Zn treatment. The result indicated an increase of intracellular free Zn ion, implying a new unreported mechanism of Zn homeostasis in leaves under the presence of both metals. Furthermore, no competition between Cd/Zn uptake and accumulation suggested the existence of independent transport system for Cd and Zn in A. halleri ssp. gemmifera, which is differed from what have been reported until now.
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