Highly distinctive population-specific thallium hyper-tolerance and hyperaccumulation in Silene latifolia

Thallium is the most toxic element known to mankind and an emerging environmental contaminant of concern. Thallium is not only toxic, but also economically valuable, and therefore novel methods for extraction from contaminated land or wastes are desirable, including phytomining using hyperaccumulator plants. Facultative hyperaccumulation is a rare phenomenon reported from a small number of widespread species in which most populations are metal sensitive, but some populations are metal tolerant and hyperaccumulating. Silene latifolia is such as facultative hyperaccumulator for thallium, and in this study, we examined population-specific thallium tolerance and accumulation trait in two metallicolous and two non-metallicolous population. The results reveal that the metallicolous populations were thallium hyper-tolerant and hyperaccumulating, attaining up to 7000 and 14,000 µg Tl g⁻¹ d.w. at the highest thallium dose level in hydroponics (60 µM), while had minimal growth reductions. In contrast, the non-metalliferous populations accumulated up to 1000 and 2000 µg g⁻¹ d.w. and had a growth reduction of 50–70 % at the highest thallium dose level. Moreover, metallicolous populations preserved photosynthetic activity and had higher ionome stability under thallium treatment, in addition to a positive correlation between thallium and sulfur in their shoots. This study revealed a striking ecotypic response in thallium tolerance/accumulation in Silene latifolia.