Metal Tolerance in Plants: The Roles of Thiol‐Containing Peptides

Abstract

AbstractChelationand compartmentalization are important mechanisms for metal tolerance in plants. Thiol‐containing peptides, i.e.,glutathione(GSH),phytochelatins(PCs), and metallothioneins (MTs), are metal ligands and play important roles inmetal tolerancein plants. This article summarizes the present knowledge about the functions of these thiol‐containingpeptidesin plant heavy metal tolerance, especially for Cd, As, and Cu. GSH participates in the amelioration of metal‐induced oxidative stress. Metal‐GSH complexes are the substrate for PC synthesis. Thus, enhanced GSH synthesis can increase metal tolerance in plants. PCs, a set of thiol‐rich peptides with the general structure (γ‐GluCys)n‐Gly, play an essential role in constitutive Cd and tolerance, whereas PCs are not involved in adaptive Cd tolerance. In contrast, PCs are required for both constitutive and adaptive As tolerance in plants. PCs may play a role in constitutive Cu tolerance in some plants, but they are not involved in Ni or Zn tolerance. MTs may play an important role in constitutive Cu tolerance, and may be involved, to some extent, in Cd tolerance in plants.