Metal Ion-Binding Properties of Phytochelatins and Related Ligands
The development of human activities and industrialization has led to an increased release of metals to the aquatic environment. Several metals (such as copper, zinc, and iron) are essential for many physiological processes but can be toxic at enhanced concentrations; others (such as cadmium, lead, and mercury) are not physiologically essential and are toxic at very low concentrations in both plant and algal cells. To cope with the deleterious effects of metals, eukaryotic cells produce strong metal-binding proteins and peptides (including the thiol phytochelatins) involved in metal tolerance and detoxification mechanisms. Plants and algae are also able to maintain the homeostasis of essential metal ions in different cellular compartments by interactions between metal transport, chelation, trafficking and sequestration activities, which regulate the uptake and distribution of these metal ions.
In this chapter, we present an overview of the metal ion-binding properties of phytochelatins and related ligands and their involvement in metal ion homeostasis, metal tolerance and detoxification mechanisms. Enzymatic processes implicated in thiol biosynthesis and regulation, and in metal ion sequestration activities, are also described. In addition, this chapter assesses our state of knowledge on the induction of thiols by phytoplankton in laboratory and field experiments.