Functional Annotation of Altered Root Metabolites and Metabolic Pathways in Spring Wheat Cultivars Under Varying Salinity and Photoperiod.

Environmental stress, particularly salinity, reduces crop yields and poses a threat to food security. While considerable research has focused on enhancing abiotic stress resilience at the leaf surface, the mechanisms of salt tolerance at the root level, especially under varying photoperiods, remain less explored. This study examined the combined effects of salinity (80 mM NaCl), normal photoperiod (nP; 12L:12D) and extended photoperiod (eP; 22L:2D) on root metabolites in two salt-tolerant (JS7, XinChun-31) and two salt-sensitive (GS-6058, Yongliang-15) spring wheat cultivars. Control plants were grown without salt stress under a normal photoperiod. Significant differences in fresh and dry root weights were observed across conditions with salt-sensitive cultivars, especially GS-6058, exhibiting improved root growth, suggesting enhanced physiological adaptation under extended photoperiods. Metabolomic analysis using liquid chromatography-mass spectrometry identified 83 root metabolites. The salt-sensitive GS-6058 showed substantial metabolic pathway perturbations under an extended photoperiod, while salt-tolerant cultivars maintained more stable metabolic profiles. Twenty pathways were significantly impacted, with alanine, aspartate and glutamate metabolism being the most significantly altered except in XinChun-31 under eP. These results underscore the modulatory role of the photoperiod in salt stress adaptation and suggest that targeting metabolic pathway biomarkers may facilitate the breeding of wheat cultivars with improved salinity resilience. Further integration of metabolite profiling with gene expression analysis is recommended to elucidate the underlying regulatory networks driving these adaptive responses.