Exploring the mechanism of exopolysaccharides in mitigating cadmium toxicity in rice through analyzing the changes of antioxidant system

Recently, exopolysaccharides (EPS) were found to alleviate cadmium (Cd) toxicity to crops by regulating the antioxidant system, but the mechanism remains unclear. Herein, by quantitative and transcriptomic approaches, a systematical map of the changes in the antioxidant system was drawn to dissected the underlying mechanism. The results demonstrated that the ascorbate-glutathione cycle (ASA-GSH cycle) is a major contributor. Specifically, compared to the control, the rice exposed to Cd exhibited a significant increase in the GSH pool (about 9-fold at 7 d), but a continuous decrease in the ASA pool (only 15.42% remained at 15 d) and an excessive accumulation of reactive oxygen species (ROS). Interestingly, with the addition of EPS, the increase of the GSH pool significantly slowed down (decreased by 180.18% at 7 d, compared to the Cd-stressed treatment), and the ASA pool remained high (consistently above 70.00% of the control group). ROS also maintained at a good level. Moreover, the activities of enzymatic antioxidants showed the similar trend. By RNA-Seq analysis, multiple genes enriched in ASA-GSH related pathway were screened (such as OsRBOHB, OsGST, OsPOD) for further study. This study provides a foundation for EPS application in agriculture, which also establishes a better way for analyzing antioxidant system.