Cellular-level thallium distribution in Biscutella laevigata revealed by X-ray fluorescence microscopy-computed tomography.

BACKGROUND AND AIMS: Biscutella laevigata is a facultative thallium hyperaccumulator, with hyperaccumulating populations known from Les Malines (France) and Cave del Predil (Italy) which are diploid and tetraploid respectively. METHODS: Biscutella laevigata was grown hydroponically and treated with 5 µM thallium. Elemental concentrations were determined with monochromatic X-ray fluorescence (MXRF) analysis. Synchrotron X-ray fluorescence microtomography was used to elucidate elemental distribution at the cellular level in plant organs. KEY RESULTS: Thallium treatment resulted in shoot concentrations exceeding 3000 µg g-1, with predominant localization in the vacuoles of the epidermal cells of leaves and at the base of the trichomes. In the root, thallium also accumulated in the epidermis, whereas most of the thallium in petioles was found in the vasculature. CONCLUSION: Biscutella laevigata compartmentalizes thallium in the epidermal vacuoles of foliar tissues as the main mechanism for detoxification of high shoot thallium.