Tarek Shalaby

Selenium and nano-selenium in agroecosystems

Selenium (Se) is an essential health element becoming rare in food as a result of intensive plant production. Indeed, several enzymes contain selenium in the form of the unusual selenocysteine amino acid. Selenium was found an essential nutrient in the late 1950s, when selenium was found to replace vitamin E in the diets of rats and chicks for the prevention of vascular, muscular, and hepatic lesions. At that time, selenium was considered solely as a toxic element in the northern Great Plains of the USA, because selenium was associated with the ‘alkali disease’ of grazing livestock. The major source of Se in soils is the weathering of Se-containing rocks. Secondary sources are volcanic activities, dusts such as in the vicinity of coal burning, Se-containing fertilizers, and some waters. Se cycles through the food system; Se is first removed from soils by plants and soil microorganisms, which can take up Se into their proteins and produce volatile forms such as dimethylselenide. Dimethylselenide enters the atmosphere to be brought down with precipitation and airborne particulates. Here, we review Se in agroecosystems. We focus on the production, biological effects, and use of nano-selenium particles.

Selenium and nano-selenium in plant nutrition

Abstract Selenium (Se) is a naturally occurring metalloid element which occurs nearly in all environments. Se is considered as a finite and non-renewable resource on the Earth. The common sources of Se in earth’s crust occur in association with sulfide minerals such as metal selenide, whereas it is rarely found in elemental form (Se0). While there is no evidence of Se need for higher plants, several reports show that when Se added at low concentrations, Se exerts beneficial effects on plant growth. Se may act as quasi-essential micronutrient through altering different physiological and biochemical traits. Thus, plants vary considerably in their physiological and biochemical response to Se. This review focusses on the physiological importance of Se forms as well as different Se fertilizers for higher plants, especially plant growth, uptake, transport, and metabolism.

Selenium and its Role in Higher Plants

Selenium (Se) is a naturally occurring metalloid element which occurs nearly in all environments in the universe. The common sources of Se in earth crust occurs in association with sulfide minerals as metal selenide whereas, it is rarely seen in elemental form (Se0). Furthermore, Se is considered a finite and non-renewable resource on earth, and has been found to be an essential element for humans, animals, micro-organisms and some other eukaryotes; but as yet its essentiality to plants is in dispute. Thus, plants vary considerably in their physiological and biochemical response to Se. Therefore, this review focuses on of the physiological importance of Se for higher plants, especially plant growth, uptake, transport, metabolism and interaction of selenium with other minerals. Biogeochemistry of Se, its relationship with S, application of Se-containing fertilizers, Se in edible plants and finally, red elemental Se nanoparticles in higher plants will be highlighted.

Selenium in Agriculture: Water, Air, Soil, Plants, Food, Animals and Nanoselenium

Selenium (Se) is an example of an essential element becoming more and more insufficient in food crops as a result of intensive plant production in many countries. Se is an essential biological trace element. It is an essential constituent of several enzymes in which it is present in the form of the unusual amino acid selenocysteine (SeCys). Se was first recognized as an essential nutrient in the late 1950s when it was found to replace vitamin E in the diets of rats and chicks for the prevention of vascular, muscular and/or hepatic lesions. Until that time, Se had been thought of only as a toxicant, being associated with “alkali disease” in grazing livestock in the northern Great Plains of the United States. Since that time, Se has become the subject of investigations in many parts of the world. Se enters soils primarily as a result of the weathering of Se-containing rocks, although volcanic activity, dusts such as in the vicinity of coal burning, Se-containing fertilizers, and some waters can also be sources. Se cycles through the food system, being removed from soils by plants and soil microorganisms, which can take up the element into their tissue proteins and metabolize some of it to volatile forms e.g., dimethylselenide. The latter enter the atmosphere to be brought down with precipitation and airborne particulates. This chapter reviews the present knowledge of the Se in agroecosystem. The occurrence of selenium in the environment from soil to food systems is discussed. The most promising and important nanotechnology applications in agriculture; and nano-selenium particles production, agricultural nanotechnology and its use in sustainable development will also be highlighted.