Cadmium Phytotoxicity: Responses, Mechanisms and Mitigation Strategies: A Review

Contamination of soils with cadmium is a critical factor affecting soil properties and plant growth. Cadmium is toxic to most plants in trace amounts, while other plants show varying tendencies to grow under relatively high cadmium levels. Some plants can bind the absorbed cadmium to their cell walls. Roots, being directly exposed, always accumulate greater amounts of cadmium than shoots. Effects of cadmium toxicity on above-ground parts include plant stunting, leaf rolling, chlorosis and necrosis, diminished stomatal conductance and gas exchange, perturbed leaf water and nutrient status, hormonal imbalance, production of oxidative stress, and enhanced peroxidation of membrane lipids. Plants use various mechanisms to cope with cadmium, which include synthesis of metal chelating proteins, expression of enzymatic and nonenzymatic antioxidants, organic acids, and plant root–mycorrhizal association. Cadmium toxicity can be alleviated by the exogenous use of metal chelators, and organic and inorganic sources. Finding strategies to bind cadmium in soil systems and better understanding of species diversity for cadmium tolerance, cadmium-responsive genes, and the molecular basis of cadmium-tolerance may be important strategies for coping with this ever-increasing problem.