Differential heavy metal tolerance of Arabidopsis halleri and Arabidopsis thaliana: a leaf slice test

Summary Here, a short‐term leaf tissue tolerance test was designed to determine the distinct Zn‐, Cd‐ and Ni‐tolerance levels for leaves of the Zn‐hyperaccumulating plant Arabidopsis halleri compared with Arabidopsis thaliana. Leaf slices were incubated in different metal concentrations for 2 h. Quantum yield of photosystem II was used as a parameter dependent on heavy metal concentrations in the incubation medium. The half effective concentration values (EC50) showed that A. halleri was extremely tolerant to Zn (EC50 » 1 m), whereas A. thaliana had an EC50 of only 2.5 mm. For Cd, the EC50 values were 40 mm and 1.9 mm for A. halleri and A. thaliana, respectively. No differential tolerance was observed for Ni between the two species. Determination of heavy metal uptake by leaf slices under the same conditions revealed decreased uptake rates for A. halleri, suggesting that low metal influx from the apoplast, probably combined with efficient intracellular compartmentation, constitutes the mechanistic basis for Zn‐ and Cd‐hyperaccumulation. It is also shown that pre‐exposure of A. halleri with Zn during growth affects tolerance in the subsequent leaf slice test. The leaf slice test presented here provides a quick and reliable method for estimating heavy metal tolerance levels in individual plants.