Elemental imaging of leaves from the metal hyperaccumulating plant Noccaea caerulescens shows different spatial distribution of Ni, Zn and Cd

Elemental imaging using laser ablation inductively coupled plasma mass spectrometry was performed on whole leaves of the hyperaccumulating plant Noccaea caerulescens after treatments with either Ni, Zn or Cd. These detailed elemental images reveal differences in the spatial distribution of these three elements across the leaf and provide new insights in the metal ion homeostasis within hyperaccumulating plants. In the Zn treated plants, Zn accumulated in the leaf tip while Mn was co-localised with Zn suggesting similar storage mechanisms for these two metals. These data show a Zn concentration difference of up to 13-fold higher in the distal part of the leaf. Also, there was no correlation between the S and Zn concentrations providing further evidence against S-binding ligands. In contrast, Ni was more evenly distributed while a more heterogeneous distribution of Cd was present with some high levels on leaf edges, suggesting that different storage and transport mechanisms are used for the hyperaccumulation of these two metals. These results show the importance of correct sampling when carrying out subcellular localisation studies as the hyperaccumulated elements are not necessarily homogenously distributed over the entire leaf area. The results also have great implications for biotechnological applications of N. caerulescens showing that it may be possible to use the mechanisms employed by N. caerulescens to increase the Zn concentration in nutrient poor crops without increasing the risk of accumulating other toxic elements such as Ni and Cd.