The Hows and Whys of Heavy Metal-Mediated Phytotoxicity: An Insight

Abstract

For the last few years, heavy metal toxicity in plants has remained as a global concern in respect to environment, agriculture, and ultimately human health. Several anthropogenic activities including modern agriculture process and industrialization cause a sharp increase in the concentration of various heavy metals in air, soil, and water. Constant increase in heavy metal concentration in the environment causes their entry and bioaccumulation in the food chain through plants. In plants, heavy metals directly or indirectly affect a broad range of physiological and metabolic processes including inhibition of photosynthesis and respiration and decrease in essential plant pigments which ultimately affect crop productivity. Inside the root cells, heavy metal ions may accumulate within various subcellular compartments of root cells, mainly vacuole and Golgi apparatus, or may be transported to different parts of the shoot through xylem cylinder by forming complex with different metal chelators. A common consequence of heavy metal toxicity in the plant cell is the elevated accumulation of reactive oxygen species (ROS) which can hamper the structure and function of crucial biomolecules including lipid, protein, and enzymes. The interaction of heavy metals with nuclear proteins, chromatin, and microtubules results in profound mitotic abnormality and genotoxicity. Plants have developed a sophisticated and coordinated system that modulates the uptake, accumulation, relocation, and detoxification of metals by highly effective homeostatic mechanisms. Various components of this network have been identified till date, including different transporters and chelators. Transporters belonging to different classes are involved in metal uptake and vacuolar transport and chelators involved in trafficking and detoxification via buffering the cytosolic metal concentrations. This chapter considers the recent progress in understanding the mechanism of heavy metal uptake and relocation and also provides insights regarding the mechanisms governing metal phytotoxicity.