Chapter 8 - Cadmium Toxicity in Plants: Unveiling the Physicochemical and Molecular Aspects

Abstract

With growing industrialization and nonjudicious use of chemical fertilizers, heavy metal–mediated chemical toxicity has become a major environmental threat for plants around the globe. Heavy metal ions cause damage to the structural, enzymatic, and nonenzymatic components of plant cells, often resulting in loss of cell viability and thus negatively affecting plant growth, development, and finally crop productivity. Like the majority of heavy metals, cadmium (Cd) enters the environment and ecosystem mainly from industrial processes and fertilizer applications and is eventually transferred to the food chain through plants. Thus, Cd toxicity is considered a major threat for humans, animals, and plants. Cd accounts for about 0.1ppm of the earth's crust. In nature, Cd contamination in soil and water generally comes from natural, agricultural, industrial, and domestic wastes. Often Cd contamination in soil may occur naturally during weathering processes. In biological systems including plants, Cd uptake mainly takes place in the form of Cd(II). After entering into plant cells, Cd generally binds to the –SH (thiol) groups of proteins and thus disrupts protein structure and function. Furthermore, Cd toxicity induces oxidative and genotoxic stress via reactive oxygen species production, which then causes oxidative damage to cellular macromolecules and the photosynthetic apparatus. The overall effects are reflected at physiological and biochemical levels with decreased membrane stability and pigment production leading to compromised photosynthetic yield, hormonal and nutrient imbalance, and the inhibition of DNA replication, gene expression, and cell division. This chapter mainly illustrates our present understanding of the physicochemical properties and molecular mechanism of Cd-mediated toxicity and stress response in plants and also highlights the importance of identifying potential targets in the associated pathways for improved tolerance to Cd stress in crops.