Redox Mechanisms and Plant Tolerance Under Heavy Metal Stress: Genes and Regulatory Networks

Abstract

Heavy metal contamination of environment is becoming increasingly serious with rapid and unchecked industrialization and urbanization. Soil contamination with heavy metals and their associated health risks have been reported in various areas globally. Plants accumulate heavy metals from soil under contaminated environments. Inside plants, heavy metals provoke numerous biochemical alterations via different metabolic processes. These biochemical alterations in plants are primarily via redox reactions which cause activation of different enzymes, modification of cell membrane permeability, replacement of essential ions, and reaction with functional groups of different molecules. Under heavy metal stress, plants have evolved numerous defense processes to tolerate heavy metal toxicity, such as sequestration into vacuoles, activation of several antioxidants, and chelation by phytochelatin/glutathione. All the biochemical changes, in plants, are mediated by a complex regulatory network of genes. The expression or overexpression of these genes and enzymes under metal stress has been revealed in some recent studies. Moreover, the heavy metal transporter proteins and transcription factors are involved in heavy metal acquisition/tolerance/homeostasis. In this chapter, we have presented an overall relation of redox mechanism and plant tolerance under heavy metal stress. We highlight the heavy metal contamination in environment, their sources in soil, accumulation by plants, their toxic effects on plants, and detoxification processes.