Thallium uptake/tolerance in a model (hyper)accumulating plant: Effect of extreme contaminant loads

Abstract

Thallium (Tl) is a toxic trace element with a highly negative effect on the environment. For phytoextraction purposes, it is important to know the limitations of plant growth. In this study, we conducted experiments with a model Tl-hyperaccumulating plant (Sinapis alba L., white mustard) to better understand the plant tolerance and/or associated detoxification mechanisms under extreme Tl doses (accumulative 0.7/1.4 mg Tl, in total). Both the hydroponic/semi-hydroponic (artificial soil) cultivation variants were studied in detail. The Tl bioaccumulation potential for the tested plant reached up to 1% of the total supplied Tl amount. Furthermore, it was revealed that the plants grown in the soil-like system did not tolerate Tl concentrations in nutrient solutions higher than ~1 mg/L, i.e., wilting symptoms were evident. Surprisingly, for the plants grown in hydroponic solutions, the tolerable Tl concentration was by contrast at least 2-times higher (≥ 2 mg Tl/L), presumably mimicking the K biochemistry. The obtained hydroponic/semi-hydroponic phytoextraction data can serve, in combination, as a model for plant-assisted remediation of soils or mining/processing wastes enriched in Tl, or possibly for environmental cycling of Tl in general.

Thallium accumulation and distribution in Silene latifolia (Caryophyllaceae) grown in hydroponics

“…This study has shown that S. latifolia accumulates Tl in response to increasing Tl concentrations in a hydroponic system. In a similar Tl dosing trial with Sinapis alba exposed to 2 mg Tl L −1 , the highest Tl in shoots was 87.2 μg g −1 (Holubík et al 2021), whereas in our experiment at 5 μM Tl (corresponding to 1 mg Tl L −1 ) S. latifolia attains 705 ± 466 μg Tl g −1 in young leaves, and even more Tl is taken up in the higher Tl treatments, thereby showing that it is demonstrably highly Tl tolerant.…”

Effect of Thallium(I) on Growth, Nutrient Absorption, Photosynthetic Pigments, and Antioxidant Response of Dittrichia Plants

“…Chang et al [ 45 ] also describe the antagonistic effect of Tl and K in Arabidopsis, in which Tl interferes with the K uptake. In Sinapis alba that are grown in hydroponic culture, the effect of Tl is to reduce the K content in the roots, as well as in the stems and leaves [ 50 ]. With regard to Mg, the Tl inhibits its absorption in Dittrichia , decreasing the content in the roots.…”

“…However, despite the increase in TF Mg and the lower effect that is observed on the Mg content in the leaves, this does not prevent the decrease in the chlorophyll content. In contrast, in S. alba , Holubick et al [ 50 ] describe low Tl concentrations leading to a decrease in Mg in shoots but not in roots, whereas, in C. annuum, the changes in the Mg content depend on the variety [ 88 ]. With regard to the Ca content, the data show that there is a decrease in its accumulation in the roots, except for those with the highest concentration that was used.…”

“…Various hydroponic culture studies have been carried out on the absorption, accumulation, and toxicity of Tl [ 46 , 50 , 51 ]. In Sinapis alba under these conditions, most of the Tl is transported to the leaves [ 50 ].…”

“…Various hydroponic culture studies have been carried out on the absorption, accumulation, and toxicity of Tl [ 46 , 50 , 51 ]. In Sinapis alba under these conditions, most of the Tl is transported to the leaves [ 50 ]. In Silene latifolia and Biscutella laevigata , low Tl concentrations induce a hormetic increase in biomass in response to slight toxic stress [ 46 , 51 , 52 , 53 ].…”