Effect of Heavy Metals on Plant Growth: An Overview

Most of the agricultural soils around the world are contaminated with heavy metals like cadmium, arsenic, mercury, lead, chromium, and many more. High concentration of heavy metals is toxic to all life forms, from microorganisms to human beings. This chapter would focus on the impacts of heavy metals on plants. High concentration of bioavailable forms of heavy metals causes production of free radicals and reactive oxygen species in plant cells. This is followed by uncontrolled oxidation and initiation of chain reaction with cellular biomolecules like nucleic acids, proteins, and lipids, ultimately causing oxidative stress and cellular damage. Therefore, sensitive plants growing in sites with heavy metals exposure show altered metabolism, growth reduction, and reduced biomass production and reduced yield. To avoid the effects of heavy metal toxicity, tolerant plants have developed numerous mechanisms that get activated on heavy metal exposure. Two broad strategies for heavy metal tolerance include sequestration/accumulation of toxic heavy metals in a cellular compartment like vacuole or apoplast, and detoxification, that is, conversion into nontoxic forms. This chapter summarizes the origin, role, and impact of heavy metals on plants, followed by plant defense mechanisms to counteract heavy metal stress, and finally, remediation techniques for removal of heavy metal contaminants.