Nickel Toxicity in Plants

Nickel (Ni) is a ubiquitous trace metal and an essential ultra micronutrient. It is a constituent of several enzymes and is currently known to be involved in a number of physiological processes in plants, including nitrogen metabolism, growth and seed germination. However, at elevated concentrations, Ni exerts multiple toxic effects on various physiological processes, which leads to impaired plant growth and morphogenesis, and reduced productivity. This review summarizes the current knowledge of the mechanisms of Ni toxicity, analyzing its effects on enzyme activity, membrane structure and functioning, antioxidant and glyoxalase systems, mineral nutrition, water regime, photosynthesis, plant growth and morphogenesis. Nickel effects on excluder plants, which accumulate Ni primarily in their roots, and hyperaccumulator plants, which accumulate Ni primarily in their shoots, are compared. Studying the mechanisms of Ni toxicity may substantially contribute to an integral modern approach to investigating plants under constantly changing environmental conditions. It is essential for understanding the full spectrum of physiological and biochemical reactions in plants that are involved in plant tolerance to Ni. Furthermore, understanding of the mechanisms of Ni growth inhibitory effects is important for the enhancement of agricultural techniques aimed at increasing crop productivity worldwide. It is also crucial for the development of approaches used in phytoremediation and phytomining technologies.