Heavy Metal Hyperaccumulator Plants: The Resource to Understand the Extreme Adaptations of Plants Towards Heavy Metals

Abstract

Heavy metal contamination of soil and water is a widespread problem throughout the world. The concentration of heavy metal is extremely high at certain sites including mainly mining-impacted areas. Phytoremediation is a low-cost, plant-based approach for the effective, feasible and acceptable remediation of metal-contaminated sites. Among various potential metal accumulator plants, hyperaccumulator plants hold a specific recognition due to their ability to survive and grow at sites having exceptionally high metal concentrations and accumulate metals in very high amounts in their shoots beyond the maximum threshold levels. The hyperaccumulator plants can accumulate a metal up to about 1--2% of total dry weight. Due to their unique features, hyperaccumulator plants have been studied extensively to delineate physiological, biochemical and molecular mechanisms involved in the metal hyperaccumulation and tolerance. The comparative evaluation of hyperaccumulators with non-accumulator plants of the same genus has yielded valuable information about differential mechanisms of combating metals. Therefore, hyperaccumulator plants have served as resource materials in understanding the extreme adaptations of plants towards heavy metal stresses. The present chapter discusses the mechanisms of metal hyperaccumulation and tolerance.