Importance of Glutathione in the Legume-Rhizobia Symbiosis

Abstract

Glutathione (GSH) is essential for the proper development of root nodules during the symbiotic association of legume and rhizobia. It is involved in the antioxidant defense, the detoxification of xenobiotics, and the tolerance to abiotic and biotic stresses. The high level of GSH in root nodules and the presence of an active ascorbate-glutathione (AsA-GSH) cycle suggest that GSH participates in the protection of the nitrogen-fixing process against reactive oxygen species (ROS) resulting from the active nodule metabolism. Glutathione-related enzymes also play a critical role in defense against ROS: (a) glutathione peroxidase (GPX) is a H2O2 scavenger that uses GSH as a reductant, (b) glutathione reductase (GR) reduces GSSG using NADPH as a source of reducing power and maintaining the GSH/GSSG ratio in cells, (c) glutathione-S-transferase (GST) catalyzes the nucleophilic conjugation of GSH with several electrophilic substrates, and (d) glutaredoxins (GRXs), small redox proteins from the thioredoxin (TRX) superfamily, use GSH as electron donor. In this chapter, the role of GSH and its related enzymes was analyzed in free-living rhizobia and in the symbiosis with the legumes as well as the responses to different abiotic stresses (acid pH, saline, drought, and heavy metals/metalloids).