Heavy metal accumulation in plants

Plants are susceptible to heavy metal toxicity and they respond to overcome these effects in a variety of different ways. The amount causing toxicity depends on the ion type, ion concentration, plant species and stage of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active transport of ions into the vacuole and formation of complexes with organic acids or peptides such as metallothioneins and phytochelatins. One of the important mechanisms for metal detoxification in plants appears to be chelation of metals by low molecular weight proteins such as metallothioneins and a family of peptide ligands, the phytochelatins. A number of metal-binding proteins and ligand peptides have been identified in plants. In recent decade molecular genetic approaches have resulted in important advances in our understanding the metal induced expression of metallothionein, phytochelatin synthase genes and phytochelatin biosynthesis. In present review the recent advances in understanding the genetic and molecular basis of the metal induced gene expression and biosynthesis and function of an important group of metal-binding peptides, the metallothionein and phytochelatins were described.