Mechanisms of heavy metal toxicity in plants

Abstract

Pollution of the environment with the toxic heavy metals has become one of the major causes for worry for human health in both emerging and advanced countries. Metal contamination issues are becoming more and more common in India and elsewhere, with many documented cases of metal toxicity in mining industries, foundries, smelters, coal-burning power plants, and agriculture. As land application becomes one of the foremost waste utilization and disposal practices, soil is increasingly being seen as a major source of metal(loid)s reaching food chain, largely through plant uptake and animal transfer. Heavy metal buildup in soils is of concern in agricultural production due to the adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. Metal toxicity has high impact and relevance to plants, and consequently, it affects the ecosystem, where the plants form an integral component. A few metals, including copper, manganese, iron, cobalt, zinc, and chromium, are, however, essential to plant metabolism in trace quantities. It is only when metals are present in bioavailable forms and at excessive levels; they have the potential to turn out to be toxic to plants through formation of complex compounds within the cell. Plants growing in metal-contaminated sites exhibit altered metabolism, growth reduction, lower biomass production, and metal accumulation. Various physiological and biochemical processes in plants are affected by metal toxicities. The present-day investigations into toxicity and tolerance in metal-stressed plants are prompted by the growing metal pollution in the environment. This article details the range of heavy metals, toxicity for plants, and mechanisms of plants to cope with metal toxicity.