Phytochelatins

Abstract

Phytochelatins (PCs) were first discovered as Cd-binding "Cadystins A and B" in a fission yeast and then in many plants as the major components of Cd-binding complexes. PCs have the general structure of (gamma-glutamyl-cysteinyl)n-glycine (n=2-11) and the variants with the repeated gamma-glutamyl-cysteinyl units are formed in some plants and yeast. They are capable of binding to various metals including Cd, Cu, Zn or As via the sulfhydryl and carboxyl residues, but their biosyntheses are controlled preferentially by the metal Cd or metalloid As. PCs are synthesized from glutathione (gamma-glutamyl-cysteinyl-glycine) in steps mediated by PC synthase. Genes (CAD1, PCS1) of the enzyme have been isolated from plants, fission yeast and some animals. Inhibition studies of PC biosynthesis via glutathione have demonstrated their fundamental roles in the metal detoxification in yeast and fungi, green algae and some aquatic plants, and also in the suspension-cultured cells and intact tissues in higher plants. Over-expression of PC synthase genes increases the Cd-tolerance in yeast and bacteria efficiently but not always in higher plant tissues especially in metal-accumulating species. "Hyperaccumulators" of Cd, Zn, Ni or As in terrestrial plants have a common feature where massive metal transport to shoots prevails, besides the ability of their roots to form PCs. This suggests that PC-based metal detoxification might be an ancient type of defense mechanism established in micro-algae or micro-fungi, and the additional PC-independent mechanism via vascular transport system became established later in higher plants. Readjustment of the PC-dependent and independent mechanisms at the metal-binding sites in the symplast and apoplast of shoots can be effective for further improvement of the metal detoxification activities and the tolerance characteristics of higher plants under various conditions.

Tolerance and prospection of phytoremediator woody species of Cd, Pb, Cu and Cr

“…Although it is an essential plant nutrient, when absorbed in large amounts it can be responsible for several types of damage at the morphological, ultrastructural and biochemical levels (Ducic´ and Polle, 2005). Copper when in excess induces oxidative stress (Yruela, 2005), leads to the formation of phytochelatin (Inouhe, 2005), binds to some ligands (Cu chaperones, metallothioneins, phytochelatins), and is sequestered in vacuoles (Clemens, 2001). Furthermore, free Cu ions are capable of irreversible binding to SH groups involved in the catalytic action or structural integrity of proteins (Van Assche and Clijsters, 1990).…”

“…Genes directly codify metallothioneins, which have low molecular weights, are rich in cysteine polypeptides and are induced by Cu (Cobbett and Goldsbrough, 2002). Phytochelatins possess low molecular weights, are enzymatically synthesized, have peptides rich in cysteine and bind to various metals including Cd, Cu (Inouhe, 2005) and Pb (Kahle, 1993) via the sulphydryl and carboxyl residues, but their biosynthesis is controlled preferentially by Cd (Inouhe, 2005). Moreover, they are associated with the intra-and extra-cellular precipitation of Pb as carbonates, sulphates and phosphates, playing an important role in the detoxification of this metal in plant tissues (Salt et al, 1998).…”

Engineering Bacteria for Bioremediation

“…Its biosynthesis is similar in plants, yeast and protists. The mitochondria and the nucleus have their own GSH reservation, which is critical or instrumental in protecting these structures against ROS action (Penninckx, 2002;Inouhe, 2005;Mendoza -Cózatl et. al., 2005).…”

“…They enable ions to bind to various heavy metal ions through thiol residues and carboxyl (Kobayashi et. al., 2005;Inouhe, 2005). These PCs are present in plants, fungi, nematodes, parasites and algae, including cyanobacteria.…”

Detection of Oxidative Stress Biomarkers Using Novel Nanostructured Biosensors

“…The low GSH levels have been found to be caused by oxidative stress and exposure to toxic heavy metals (Hg, Cd, Pb). GSH and phytochelatines with general structure (γ-GluCys) n Gly participate as the capping agents (Barbas et al, 1992, Dameron et al, 1989 in heavy-metal sulfide nanoparticles formed in living organisms in natural detoxification processes (Inouhe, 2005, Mehra et al, 1991, Vatamaniuk et al, 2000, Vatamaniuk et al, 2001. While the kinetics of a systemic response to an oxidative stress is basically dependent only on the GSH level, the redox potential depends on both the GSH and GSSG.…”