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

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 much greater than 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.