Format: ORAL

Mirko Salinitro1, Sandrine Isnard2, Dennis Brueckner3, Kathryn M. Spiers3, Mark G. M. Aarts4, Amelia Corzo Remigio5, Antony van der Ent4

1 University of Bologna, Bologna, Italy. 2 Université de Montpellier, Montpellier, France. 3 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany. 4 Wageningen University and Research, Wageningen, The Netherlands. 5 The University of Queensland, Brisbane, Australia.

Thallium (Tl) is a relatively rare element, but highly toxic for all living organisms already at low concentrations. Some plant however evolved Tl hyperaccumulation and the most extreme Tl hyperaccumulator is Biscutella laevigata capable of attaining 32,000 g Tl g-1 in its leaves. Interestingly, only some ecotypes have the ability to hyperaccumulate Tl when growing on Tl-rich soils. The study aims at understanding the Tl handling mechanisms, tolerance and distribution in two ecotypes ofB. laevigata using synchrotron-based X-ray fluorescence microscopy. Two B. laeavigata accessions were used in this study coming from: Les Malines (France, Tl-hyperaccumulator) and Feltre (Italy, non-accumulator). Both accessions were grown in aeroponics for two months and were subjected to three Tl treatments: 0 (control), 5 and 30 M. The two accessions showed morphological differences in terms of leaves shapes and trichome distribution, with Les Malines having deeply lobate leaves and scarce trichomes compared to Feltre with almost entire leaves and dense trichomes.Overall, Les Malines accession showed greater Tl tolerance and accumulation, compared to Feltre, which did not survive in the 30 M Tl treatment. Feltre accession accumulated 125 g Tl g-1 in old leaves (at 5 M), whereas Les Malines accession had 1750 and 24,130 g Tl g-1 in old leaves (at 5 and 30 M respectively). The distribution of Tl was similar in the two accessions. The synchrotron XRF analysis revealed that Tl is localised in the vacuoles of epidermal cells, especially in trichome basal cells. Thallium also occurs in solid crystalline deposits (35 m in size, ~40 wt% Tl) that are mainly found in guard cells of stomata and in foliar margins.Other studies need to be carried out including more accessions, and including transcriptomics to yield information on the genes and genetic pathways linked to the phenotypic variation in Tl hyperaccumulation.