Harnessing the anti and pro-oxidants potential of selenium

Selenium is an essential trace element with a dual role in plant physiology; it acts either as a pro-oxidant or as an antioxidant depending on its concentration and chemical form. A plant assimilates Se present in the soil, which constitutes the main determining factor for its availability due to the presence of different forms (e.g. selenite, selenate, organic Se). Efficient uptake facilitates the assimilation of Se mostly through sulfate transporter genes. Once inside the plant, selenium undergoes complex speciation, transforming into organic compounds like selenomethionine and selenocysteine, which are then distributed throughout the plant tissues. As an antioxidant, selenium plays a crucial role in enhancing plant stress tolerance. Being part of selenoenzymes, e.g. glutathione peroxidase (GPx) and thioredoxin reductase (TrxR), selenium can neutralize reactive oxygen species (ROS) produced inside the cells, protecting them from oxidative deterioration. Selenium treatment enhances the enzyme activities of antioxidation and the accumulation of non-enzymatic antioxidants in plants, thus improving resistance to abiotic stress such as drought, salinity, and heavy metal toxicity. Reaching a higher level, selenium opposes its antioxidant activity and turns into pro-oxidants. Selenium toxicity in plants is characterized by a redox imbalance, causing excessive production of certain types of ROS and their related oxidative stress. This pro-oxidant activity further compounds cellular damage since it may disrupt the metabolism of essential metals. To apply selenium safely, it is important to know precisely at what concentrations it ceases to have beneficial effects on health. Despite these challenges, selenium biofortification may be a good method to improve the nutritional quality of crops and to uplift human health. Selenium-enriched crops are one of the key food sources of this vital trace element necessary for antioxidant defense and immune function in humans. Future research should focus on optimizing selenium biofortification protocols to maximize the antioxidant properties of selenium while minimizing the risk of pro-oxidant effects so as to promote sustainable agriculture and human nutrition.