Physiological and Molecular Responses to Heavy Metal Stresses in Plants

In recent times, anthropogenic perturbations (extensive mining, modern agricultural practices, accelerated industrialization, etc.) of environment have led to the accumulation of heavy metals in air, water and soil. Soil pollution with heavy metals (Zn, Cu, Mo, Mn, Co, Ni, As, Pb, Cd, Hg, Cr, Al and Be) prompts various environmental issues and confers harmful effects in plants such as morphological abnormalities, metabolic disorders and production of reactive oxygen species (O2, H2O2 and OH−), which ultimately end up in yield loss in plants. With regard to these unfavourable environments, plants develop a wide range of exceptionally complex mechanisms and responses to acquire tolerance and survival, which include activation of various antioxidants, binding to phytochelatins/metallothioneins, sequestration of metal into vacuoles, etc. This chapter describes the plant response to metal stress, signalling molecules, toxic effects, functions and detoxification capabilities of phytochelatins, metallothioneins, amino acids, organic acids and chaperones and the role of plant-associated microbes. Moreover, heavy metal-induced oxidative stress with tolerance and crosstalk is also addressed.