Heavy metal specificity of cellular tolerance in two hyperaccumulating plants, Arabidopsis halleri and Thlaspi caerulescens

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Abstract
• The cellular tolerance to nickel (Ni), zinc (Zn) and cadmium (Cd) of two poly-hyperaccumulators, Arabidopsis halleri and Thlaspi caerulescens, was investigated in order to compare their cellular phenotypes toward various metal ion exposures. • Protoplasts were kept for 24 h on solutions containing increasing concentrations of the metal ions, and a viability test was performed. Zinc loading of the protoplasts was investigated with Arabidopsis lyrata and A. halleri protoplasts using the Zn fluorescent indicator Newport green diacetate. • Only T. caerulescens protoplasts showed a clear tolerance to Ni. On the other hand, protoplasts from both hyperaccumulators displayed a very high and constitutive Zn tolerance and an inducible Cd tolerance. The vacuolar storage of Zn was confirmed, but no Zn accumulation at all was observed in A. halleri protoplasts after Zn exposure. • Specific metal tolerances were found at the cellular level in the hyperaccumulating plants, highlighting that specific adaptations to metal ions exist in the cells as well as in the whole plants.