Decoding the antioxidant mechanisms underlying arsenic stress in roots of inoculated peanut plants

Abstract

Arsenic (As) has aroused worldwide concern due to its accumulation in the food chain. Inoculated peanut plants with Bradyrhizobium sp. strains showing contrasting tolerance to arsenic (As), were exposed to a low arsenate (AsV) for 30 days in order to decipher the participation of the antioxidant system, mainly related to glutathione (GSH) metabolism, together with the arsenate reductase (AR) activity in roots. Results showed that the Bradyrhizobium sp. strain modulates differentially the AR activity. An increase in the enzymatic activities of superoxide dismutase, glutathione peroxidase/peroxirredoxin and glutathione S-transferase (GST) was observed, while glutathione reductase (GR) and monodehydroascorbate reductase activities were diminished. Particularly, ascorbate peroxidase (APX) activity was reduced when C-145 was inoculated. Gene expression assays reported an increase in the expression of transcripts GR, cAPX and GST in peanut roots inoculated with SEMIA6144. In the system peanut-Bradyrhizobium sp. C-145, the cAPX expression remained unchanged. In both symbiotic interactions, the total glutathione (GSHT) and reduced glutathione (GSHR) contents diminished, while oxidized glutathione (GSSG) increased leading to a reduction in the GSHR/(GSHR + GSSG) ratio. We conclude that, irrespectively of the As tolerance that the inoculated strains shows, the antioxidant response is not strain dependent. Thus, glutathione plays a fundamental role not only as an antioxidant metabolite but also as a key molecule to enhance metalloid detoxification in this inoculated crop. Moreover, as the tripeptide participates in the ROS scavenging, acting mainly as a substrate for GST, allow us to describe its activity as a robust biomarker of arsenic contamination in crops.