Untargeted metabolomics analysis in tolerant and susceptible landraces of rice under sodicity stress

Sodicity is a major abiotic stress affecting rice production by disrupting soil structure and impairing major physiological processes in plants. Landraces possess high genetic diversity and exhibit strong adaptation to diverse environmental stresses, including sodicity. In the present study, we screened 47 landraces and identified Norungan as highly tolerant to sodicity based on morpho-physiological traits. Further, we characterized the biochemical and metabolic responses of Norungan and Vellai Kudaivazhai (Highly susceptible landrace) under control and sodicity stress conditions. Biochemical analysis revealed that efficient photosynthesis, reduced lipid peroxidation, and elevated antioxidant enzyme activities distinguished Norungan from Vellai Kudaivazhai and provided primary evidence supporting its tolerance. Untargeted metabolomics analysis of Norungan and Vellai Kudaivazhai identified 103 and 117 differentially accumulated metabolites (DAMs), respectively. The DAMs in Norungan indicated more efficient energy utilization through the TCA cycle and GABA shunt compared to Vellai Kudaivazhai, along with effective sucrose homeostasis that minimized carbon leakage via dead cells. Although, Norungan exhibited effective sucrose homeostasis, minimizing carbon leakage through dead cells, the upregulation of major osmolytes, such as proline (Fold change – 5.32) further underscored its tolerance. Additionally, the enrichment of pathways such as starch and sucrose metabolism, and the TCA cycle, highlighting Norungan's adaptive mechanisms underlying sodicity tolerance. Taken together, these findings provide valuable insights into the mechanisms of sodicity tolerance, which may inform targeted breeding strategies aimed at improving sodicity tolerance in rice.