Metabolomic insights into the mechanisms of chickpea milkvetch (Astragalus Cicer L.) response to salt stress

Soil salinization severely impacts plant growth and development, limiting the advancement of agro-ecological economies. Astragalus cicer, a highly efficient ecological grass, green manure crop, and high-quality protein forage. However, the molecular mechanisms underlying its root response to NaCl stress remain poorly understood. In this study, the A. cicer cultivar ‘Ganlü No. 2’ was treated with 150 mM NaCl over different time periods to investigate the physiological and metabolomic mechanisms underlying its adaptation to saline conditions. A. cicer exhibited concentration-dependent growth responses to NaCl treatment: a low salt concentration (50 mM) promoted early growth, whereas a high salt concentration (150 mM) induced pronounced oxidative stress and inhibited plant growth. Metabolomic analysis identified 1,677 differentially accumulated metabolites (DAMs). During the early stress phase, roots rapidly accumulated key signaling molecules, including cAMP, cGMP, and the cytokinin dihydrozeatin, suggesting the swift activation of the cAMP/cGMP signaling pathway to initiate the stress response. By the mid-term phase, the metabolite profile exhibited dynamic adjustments, with sustained high levels of cAMP and dihydrozeatin, while antioxidant metabolites such as rosmarinic acid were significantly downregulated. KEGG pathway enrichment analysis consistently highlighted the enrichment of purine metabolism and cysteine/methionine metabolism across all time points, underscoring the pivotal roles of nucleotide and sulfur-containing amino acid metabolism in the long-term adaptation of roots to NaCl stress. Clustering and Short Time-series Expression Miner (STEM) analysis further revealed significant temporal specificity in DAM expression, with prominent enrichment in pathways such as secondary metabolite biosynthesis, flavonoid biosynthesis, phenylpropanoid metabolism, purine/pyrimidine metabolism, and amino acid biosynthesis. A. cicer exhibits a dynamic adaptive response to NaCl stress, rapidly activating signaling pathways and coordinating the regulation of core metabolic pathways, including nucleotide metabolism, sulfur-containing amino acid metabolism, and secondary metabolism. These findings provide important molecular insights into the salt tolerance mechanisms of this species and offer valuable information for salt-tolerant breeding strategies.