Biscutella update: thallium and metal tolerance tests

The following work was presented at ICOBTE 2011 as a poster.

Thallium is a toxic heavy metal which pollution can derive from anthropogenic or pedogeochemical sources.

In our previous analysis we reported a presence of Biscutella laevigata subsp. laevigata in the former mining area of Cave del Predil, Tarvisio (Italy) (Fellet et al., 2011). In those specimens the average shoot Tl concentration was above the threshold for hyperaccumulation (> 1,000 ppm).

Biscutella laevigata subsp. laevigata on maining tails at Cave del Predil (Italy)

Plantlets from three geographically distant metallicolous [Cave del Predil (Cap), I and Ganges (Gan), F) and nonmetallicolous (Codroipo (Cod), I] B. laevigata subsp. laevigata populations were tested for Tl tolerance and accumulation for 8 days at increasing concentrations of Tl. You can see in the following picture how the tollerant populations develop more roots (white filaments) comparing to the non tolerant at 10 ppm Tl in solution.

The main findings were:

• The Cap population had the highest indices of tolerance in root elongation test and Tl concentration in shoots (up to 28,746 mg kg-1) and roots (up to 16,086 mg kg-1);
• A hyperacumulator Tl population of B. l. subsp. laevigata differentiation occurred in Cave del Predil;
• The Tl tolerance and accumulation is probable constitutive and adaptive;
• A phytomining of Tl by Cap population is a promising technique for soil remediation and for obtaining this rare, required and expensive metal (5,930 $ Kg^-1 in 2010).

As Tl is not a redox metal therefore cannot yield hydroxyl radicals, it may cause oxidative stress in plants by disturbing the Photosystem II that will lead to greater production of Reactive oxygen species in nontolerant plants. Further studies on oxidative stress are on-going in Free University of Amsterdam.