**7.1 Selenium uptake**

Selenium exists as both as organic (seleniumcysteine (SeCys) and seleniummethionine (SeMet)) and inorganic (selenate (SeO4 <sup>2</sup>−), selenide (Se2<sup>−</sup>), selenite (SeO3 <sup>2</sup><sup>−</sup>) and selenium (Se)) [61, 62]. The various species of plants, their developmental phases, type and concentration of selenium, the soil pH and its salinity determines the uptake and distribution of selenium in plants [14, 16]. Selenate is the most bioavailable form of selenium in agriculture and it is also more soluble in water than selenite [63]. Selenite is found in acidic soils, whereas selenate is found in alkaline soils [14]. According to Kikkert and Berkelaar [64], the rate of translocation of selenate is higher than that of selenium methionine while that of selenium methionine is greater than that of selenite or selenium cysteine by studying the translocation factors. Uptake of selenium is mostly carried out by transporters in the cell membrane of the root; selenate is transported by sulfate transporters while selenite is transported by phosphate transporters [14, 65]. The plants nutritional state determines the choice of the transporters [66]. Transporters for selenium decrease under extreme sulfate concentrations while the inducible transporters show greater affinity for sulfate than selenate than the constitutive ones [66]. Lack of sulfur and phosphorus in *Triticum aestivum* enhanced the uptake of selenium [14].
