ABSTRACT
This chapter addresses the role of two types of metal ligands, phytochelatins and metallothioneins, in tolerance of plants to heavy metals. Phytochelatin (PC) synthesis in plant cells and PC synthase activity can be induced by a wide variety of metal ions, and PCs are able to bind a number of metal ions in vitro through thiolate bonds. Plants that are selected and developed for phytoremediation will need to have a number of advantageous physiological traits, including tolerance of metals and other environmental conditions at the contaminated site, enhanced uptake and transport of metals, and sequestration of metals in shoot tissues. While cloning a gene for PC synthase has not yet been accomplished, altering the expression of this gene in plants may not have a significant impact on metal tolerance. The enzyme is constitutively expressed in many tissues, and its activity is regulated by free metal ions.
