Plant transporters involved in heavy metal homeostasis

Transition metal ions (predominately manganese, iron, cobalt, nickel, copper and zinc) have an array of catalytic and regulatory roles in the growth and development of all living organisms. However, an excess of these metal ions can also be toxic to any life form and therefore every cell and whole organism needs to maintain the concentration of these essential nutrient metals within a narrow range: a process known as metal homeostasis. Heavy metal ions are taken up into cells by selective transporters and as they cannot be degraded, the “desired” levels of metal ions are achieved by a number of strategies that involve: chelation, sequestration and export out of the cell. Cation Diffusion Facilitators (CDF) is a large family of transporters involved in maintaining the cytosolic metal concentration. They transport different heavy metal divalent ions, but exhibit main affinity for zinc, iron and manganese. Metal Tolerance Proteins (MTPs) are a subfamily of the Cation Diffusion Facilitator (CDF) family found in plants. There has been much interest in these heavy metal transporters in order to provide an insight into plant metal homeostasis, which has significant implications in human health and phytoremediation. Although data regarding the CDFs/MTPs mechanism is gathering there is still little information with respect to metal selectivity determinants.