Heavy Metal and Their Regulation in Plant System: An Overview

Abstract

Unplanned industrialization and improper waste disposal have resulted in the release of enormous quantities of inorganic toxicants like metal, metalloids, and radionuclides in the biosphere. Since, metals are non-biodegradable and tend to bioaccumulate via food chain, they pose threat to human health. Indiscriminate disposal of industrial waste to the environment causes adverse impact on ecosystem. Plants growing on metal-contaminated sites display several disturbances related to physiology and biochemical process like gaseous exchange, CO2 fixation, respiration, nutrient absorption, etc. These disturbances subsequently cause reduction in plant growth and lower biomass production. Although being an essential micronutrient, some heavy metals at lower concentrations are vital for plant growth; however, at higher concentrations they become very toxic. To cope up with the metal toxicity, plants have developed various mechanisms like immobilization, exclusion, chelation, and compartmentization. Plants have distinct cellular mechanism such as chelation and vacuolar compartmentization of metals to withstand the metal toxicity. Phytochelatins, the thiol peptides, potentially chelate metals and form complexes in cytoplasm; subsequently these metal-thiol complexes are sequestrated into vacuole via ATP-binding cassette transporters (ABC transporters). In the last couple of decades, the role of phytochelatin synthetase (PCS) and phytochelatins (PCs) in metal detoxification has been proven. In present scenario, there is a great need of sound and intensified research for better understanding of metal toxicity and its metabolism in plants to maintain our ecological harmony.