||Contamination of soil and water with heavy metals and metalloids is a worldwide problem today. The beneficial effect of silicon for optimal plant performance and agricultural crops exposed to various types of abiotic stress (studied in our previous projects) have been reported by several authors, though the mechanism of its action is still not fully understood. The aim of the project is to study the mechanisms of action of exogenously applied silicon on the defense responses of the selected cultivars of maize (or other crops – wheat and sunflower) exposed to toxic (As, Sb) and potentially toxic (in excess) essential elements (Cu) on metabolic and biochemical levels. We will focus on growth, physiological processes (membrane damage, water intake and release, etc.), changes in nitrogen metabolism and its possible connection with antioxidant mechanisms (glutathione-ascorbate cycle), as well as non-enzymatic and enzymatic components of the antioxidant defense system in individual organs of experimental plants.