Effects of selenium on plant metabolism and implications for crops and consumers

Selenium (Se) is an essential trace element for many organisms including humans, while in plants it can trigger a variety of beneficial effects. Plants absorb Se mainly in the form of selenate using high affinity root sulfate transporters. Consequently, availability of sulfur (S) has a major impact on Se accumulation due to competition effects of the two oxyanions. In addition, Se has an impact on S uptake through interference with intrinsic regulatory mechanisms. Inside cells, selenate can access the sulfate assimilation pathway and influence the production of S-organic compounds that are of vital importance in plant responses to biotic and abiotic stress conditions. Selenium has been reported to mitigate stress in plants because of its capacity to induce the synthesis of S- and nitrogen (N) compounds, in addition to stimulating the activity of antioxidant enzymes and metabolites. Selenium can also alter the uptake of certain microelements like molybdenum, which functions as a cofactor for the enzyme nitrate reductase. Therefore, Se at high doses may interfere with N assimilation, causing a decrease in the level of N-compounds with structural and/or regulatory functions. Selenium interactions with multiple metabolic pathways in plants have relevant implications for plants and consumers that feed on them. Managing such interactions are useful to biofortify crops with organic forms of Se endowed with beneficial properties (selenomethionine and methylselenocysteine) and in other nutraceuticals like glucosinolates and antioxidants. Furthermore, Se at low doses may improve plant productivity or phytoremediation potential by enhancing photosynthesis and increasing the capacity of plants to tolerate stress.