Uncovering the physiology and distribution of thallium in Tl-hyperaccumulating and Tl-sensitive populations of Biscutella laevigata L.

BACKGROUND AND AIMS

Thallium (Tl) is extremely toxic to all lifeforms and an emerging pollutant. Plants in the Brassicaceae family, including edible crops, have an enhanced capacity for Tl accumulation, even from soils with low thallium concentration. The most extreme Tl hyperaccumulator is Biscutella laevigata, capable of attaining >32,000 μg Tl g-1 DW in its leaves.

METHODS

Biscutella laevigata from a non-metallicolous accession (Feltre, Italy) and a metallicolous accession (Les Malines, France) were subjected to a dosing experiment in hydroponics (0, 5, 30 μM Tl), followed by synchrotron-based µXRF analysis to elucidate tissue and cellular-level Tl distribution.

KEY RESULTS

Flow cytometric data on the two used accessions showed the Feltre accession has a genome size twice of that of the Les Malines accession (256 and 125 pg/2C respectively), suggesting they are phylogenetically distant populations. The Feltre accession does not accumulate Tl (125 μg Tl g-1 DW on average in leaves) at the 5 µM Tl dose level, whereas the Les Malines accession had a mean of 1750 μg Tl g-1 DW, with peaks of 24,130 μg Tl g-1 DW at the 30 µM Tl dose level. At 30 µM Tl the non-metallicolous accession did not grow, and at 5 µM Tl showed reduced biomasss compared to the metallicolous one. In Les Malines accession, the synchrotron-based µXRF analysis revealed that Tl is localised in the vacuoles of epidermal cells, especially underneath trichomes and in trichome basal cells. Thallium also occurs in solid crystalline deposits (3-5 µm in size, ~40 wt% Tl) that are mainly found in foliar margins and under trichome bases.

CONCLUSIONS

Biscutella laevigata is an attractive model for studying Tl hypertolerance and hyperaccumulation on account of the extreme expression of this trait, and its marked intraspecific variability.

Informations de copyright

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