Physiological and molecular mechanisms of heavy metal uptake by hyperaccumulting plants

The mechanisms of heavy metal hyperaccumulation in the leaf cells by the hyperaccumulating plant species are not fully understood. Heavy metal transport from the rhizosphere to the shoots could be regulated at several different sites within the plant. These processes include metal ion influx across root plasma membrane, transport within the root symplasm, loading into xylem vessels in the stele of the root, long distance translocation in the xylem (and possibly phloem), transports across the leaf cell membrane and the leaf cell tonoplast, and storage in the vacuole. In this paper, recent advances in understanding physiological and molecular mechanisms of heavy metal absobtion, transport and accumulation by the hyperaccumulating plants were reviewed.