The regulatory and signaling roles of glutathione in modulating abiotic stress responses and tolerance

Abstract

Glutathione (GSH) plays a key role in the maintenance of tissue antioxidant defence and in the regulation of redox-sensitive signal transduction. The size of the GSH pool and its redox status are strongly correlated with the tolerance of plants. The effect of GSH on plant stress resistance is achieved mainly through the cycle of ascorbate (AsA)-GSH producing dehydroascorbate (DHA) re-reduction, in which GSH is intermediate in the recycling of H2O2 reduction and the recycling of GSH is regulated by the glutathione reductase (GR) enzyme. Under oxidative stress, H2O2 and reactive oxygen species (ROS) can be reduced by GSH, while GSH is oxidized to oxidized glutathione (GSSG). Under normal physiological conditions, GSSG can be reduced to GSH by GR in the presence and with the involvement of NADPH, thus creating the redox cycle. AsA/DHA, GSH/GSSG, NADPH/NADP are the three most important interconnected and coordinated redox pairs in plant cells, and plants can scavenge ROS and strengthen their resistance to abiotic stresses by modulating the status of redox pairs; thus the redox metabolism pathways are initiated by diverse environmental stresses. In addition, GSH can regulate the ROS signal transduction pathway, and ROS levels depend on the redox status of redox pairs in plant cells. GSH can activate the genes involved in phytoalexin biosynthesis to repress the accumulation of plant toxin. H2O2 can strengthen this effect through the up-regulation of GSSG. When H2O2 reaches a higher level, the biosynthesis of GSH is stimulated, while GSH, on the other hand, can mediate the response of the plant to the H2O2 signal.