Positive influence of selenium on the modulation of ascorbate-glutathione cycle in salt stressed Setaria italica L

Soil salinity is a significant abiotic factor affecting crop yield and global distribution, hence selecting salt-tolerant crop species is crucial for food security. Foxtail millet is a resilient crop suitable for hilly, salinity, and drought-prone areas due to its ability to withstand environmental stressors. In this study, foxtail millet was subjected to high NaCl concentrations (150 mM and 200 mM) and selenium (1 μM, 5 μM, and 10 μM) as a stress mitigator. Increased salinity in foxtail plants hampered the growth with decreased pigment levels, increased H₂O₂ levels (153.6%), lipid peroxidation (32.1%), and electrolyte leakage (155.5%). The application of 1 μM Se positively influenced the root-to-shoot ratio (R) (59.2%), photosynthetic pigments, phenolic content (25.1%), flavonoid content (7%) and hence the antioxidant potential of the salt stressed plants there by decreasing the H₂O₂ levels (26.8%) and suggesting a greater ability to scavenge radicals. Both NaCl and Se induced the AsA-GSH pathway. Se supplementation significantly improved AsA-GSH pathway components such as AsA/DHA (40.8%) and GSH/GSSG ratios (39.6%) in salt-stressed foxtail millet, reducing oxidative stress and efficiently neutralizing H₂O₂. Gene expression validation confirmed that SiAPX, SiDHAR, SiMDHAR, and SiGR showed significant upregulation with 1 μM Se application in salt-stressed foxtail millet plants. However, higher Se concentrations (5 μM and 10 μM) led to a reduced fresh weight along with R, increased the MDA and H₂O₂ levels, and did not positively contribute to osmolyte accumulation or improve the AsA/DHA and GSH/GSSG ratios. Elevated Se levels also led to a decreased antioxidant potential. Among the enzymes of the AsA-GSH cycle, higher Se concentrations negatively affected APX, DHAR, MDHAR, and GR activities, indicating stress aggravation rather than mitigation at elevated doses.