Biochemical and Molecular Aspects in Phytoremediation of Selenium

Abstract

The element selenium (Se) is considered a finite and non-renewable resource on earth, and has been found to be an essential element in humans, animals, micro-organisms and some other eukaryotes; but as yet its essentiality to plants is in dispute. There is no doubt that adequate levels of selenium are important to animal and human health, and some selenium compounds have been found to be active against cancers. A limited number of plants growing on selenium rich soils can accumulate very high levels of selenium (i.e., hyperaccumulate selenium), and are classified as selenium tolerant, however, many more plants do not accumulate selenium to any great extent, and are selenium sensitive. Plants vary considerably in their physiological and biochemical response to selenium, and a revision of the physiological responses of plants to selenium is presented; especially growth, uptake, transport and interaction of selenium with other minerals. The review also details the biochemical responses of plants to selenium, the assimilation of selenium in plants and possible incorporation into proteins. Molecular approaches to understanding selenium toxicity and tolerance have increased the knowledge of mechanisms of action, and the molecular biology of selenium in transgenic plants is detailed; with special reference to the similarity with sulphur metabolism, sulphur/selenium transporters and important assimilation enzymes. Phytovolatilisation of selenium will be summarised, which is a unique method for plants to metabolise selenium to more volatile forms in order to eliminate selenium from tissues, and eventually from the soil and water. Finally, the application of phytoremediation in selenium rich environments is reviewed in light of the possible use of plants to decontaminate selenium from soil and water environments, and perhaps also produce a product which could be used in mineral supplementation of foods, and even fighting cancers.