Selenium (Se) is an essential nutrient for many organisms, but also toxic at higher levels. Se deficiency is one of the urgent questions. Around 15% of the world’s population is estimated as Se deficient in various degrees. Se is a vital component of aminoacids, selenoproteins, and selenium-binding proteins that can easily transform into aminoacids instead of sulphur (S). Among different Se supplementation options, diet is the principal route even for animals and humans. Most people obtain virtually all of their Se from the foods they eat. In plant and animal tissues, Se is found mostly bound to proteins. Considering the diet, plants have outstanding importance. They may be used both to provide dietary Se in areas of Se deficiency, and to clean up Se pollution from seleniferous areas. Plant foods are the major dietary sources of Se in most countries throughout the world, and Se imbalance in the soil-plant system can lead to production of Se-deficient food with negative consequences for human and animal nutrition. However plants don’t need Se to keep the normal metabolism, they can transform inorganic Se to organic selenoaminoacids and their derivatives. Beside the advantages for humans and animals, Se improves plant growth and other physiological parameters. Our new scientific results were: Sunflower has high Se accumulation capacity and has a high Se tolerance capacity in phytoremediation cultures and also as a Se-hyperaccumulator; by up taking near 1800 mg kg-1 (in range) in shoots can be a valuable plant for agricultural industry, phytoremediation processing and biofortification. 3 mg kg-1 of SeIV significantly increases green pea growth biomarkers and protein content in the leaves significantly by 17% and also selenomethionine (SeMet) is the major species especially in shoot and the only organic selenium form in lower SeIV concentration range. Elevated dosage of SeIV (≥30 mg kg-1) results inhibitive effects on growth and protein content and causes higher accumulation of inorganic Se in forms of SeVI and SeIV along with selenocysteine (SeCys2).