Modulation of glutathione and its related enzymes in plants' responses to toxic metals and metalloids-A review

The rapid increase in the contamination of the environment by toxic metals (TMs) and metalloids is posing serious threats to biotic communities. Plants are among the organisms most vulnerable to TMs and metalloids due to their sedentary and stationary existence under changing environmental conditions. Toxic metals- and metalloids-stress-impacts cause either directly or indirectly excessive generation of reactive oxygen species (ROS) leading to oxidative stress in plants. Being a significant component of ascorbate-glutathione (AsA-GSH) pathway, tripeptide glutathione (GSH, gamma-Glu-Cys-Gly) is involved in both direct and indirect control of ROS and their reaction products concentrations in cells and thus, protects plants against TMs- and metalloids-mediated oxidative stress. Additionally, several GSH-related enzymes such as GSH reductase (GR, EC 1.6.4.2), GSH peroxidases (GPXs, EC 1.11.1.9) and GSH sulfo-transferases (GSTs, EC 2.5.1.18) cumulatively form an efficient defense system to protect plants against ROS-inducecl effects in addition to their significance for the detoxification, chelation and compartmentalization of major TMs and metalloids in plants. The present review critically evaluates the recent studies on the modulation of total reduced GSH, GSH/GSSG redox couple, the major GSH-related enzymes and their cumulative significance in plants' adaptation and/or tolerance to TMs and metalloids in detail. (C) 2011 Elsevier B.V. All rights reserved.