The effects of rhenium accumulation on Indian mustard

Rhenium (Re) is one of Earth's scarcest and more largely scattered elements, with an estimate concentration of 0.4-0.6 μg kg^-1 in the upper crust. Still, considerable concentrations of bioavailable ReO₄^- ions are often found, particularly in copper-molybdenum mines, where their uptake by plants of these regions has been reported. Yet, the impact of Re on plants remains a question mark, as the only available knowledge derives from a limited investigation carried out over 60 years ago. The aim of this study was to evaluate the ecophysiological response of Brassica juncea, a species known to endure and accumulate various metals, to a broad range of Re concentrations. B. juncea plants were allowed to grow and on a substrate amended with KReO₄ to attain soil Re levels ranging from 0 to 80 mg kg^-1. Plants were collected 45 days after sowing for analysis. The results have shown that greater Re levels reduce growth, photosynthetic activity, soluble carbohydrate mobilization, and protein contents, and increase the plant's oxidative stress (anthocyanins, H₂O₂, lipid peroxidation) and corresponding response (ascorbic acid, superoxide dismutase activity). Nevertheless, B. juncea exhibited a remarkable ability to endure and uptake Re, featuring shoot Re concentrations that ranged from 1615 to 24,987 mg kg^-1 among the 5 and 80 mg kg^-1 treatments.