Effects of selenium on the uptake of toxic trace elements by crop plants: A review

Selenium (Se) is an essential micronutrient for humans and animals and can have beneficial effects on plants. A low concentration of Se can improve plant growth; however, high concentrations can be toxic for plants. In addition, Se can counteract stresses from toxic trace elements in plants. Hence, improved knowledge of the mechanisms involved may contribute to more effective management of Se for reducing trace element stress in plants. Here, the mechanisms of Se-mediated reduction of trace element toxicity in plants are reviewed. Upon uptake by plants, Se may protect plants against toxic trace elements by enhancing plant growth and photosynthesis by regulating the uptake and translocation of trace elements, and by mitigating oxidative stress through regulation of reactive oxygen species. Furthermore, within the plant, Se-induced tolerance of toxic trace elements involves modification of gene expression, chelation, compartmentalization within plants, and changes in the trace element species. In the rhizosphere, complexation of Se with toxic trace elements may contribute to a reduced uptake of these elements by plants. There is a need to explore the mechanisms of Se-induced trace element tolerance in plants at the molecular and genetic levels. Furthermore, field studies are needed to determine the optimal levels of Se.