Dopamine enhances salinity tolerance and elicits diosgenin biosynthesis in fenugreek (Trigonella foenum-graecum L.)

Abstract Background Salinity stress compromises crop quality and yield, threatening food security and seriously constraining sustainable agriculture. Dopamine (DA) has emerged as a promising elicitor for enhancing stress tolerance and the quantity and quality of secondary metabolites, yet its role in salinity tolerance and diosgenin biosynthesis in fenugreek ( Trigonella foenum-graecum L.) remains unknown. This study evaluated the physiological, biochemical, hormonal, and molecular responses of fenugreek plants to exogenous DA (0, 100, 200, and 400 µM) under salinity (0, 150, and 300 mM NaCl), focusing on diosgenin biosynthesis. Results Severe salinity decreased total chlorophyll (54%), relative water content (59%), and K⁺/Na⁺ ratio (0.86), while increasing lipid peroxidation, electrolyte leakage (EL), hydrogen peroxide (H₂O₂), abscisic acid (ABA), nitric oxide (NO), and endogenous DA. Among treatments, 200 µM DA was most effective, increasing total chlorophyll (8.59 to 15.60 mg g⁻¹ FW; 80%), water content (51.6% to 65.6%; 28%), K⁺/Na⁺ (0.38 to 0.94; 147%), NO (29 to 37.33 µmol g⁻¹ FW; 40%), ABA (26.49 to 40 ng g⁻¹ FW; 51%), auxin (13.96 to 25.82 ng g⁻¹ FW; 84%), and endogenous DA in shoots (6.60 to 10.60 ng g⁻¹ FW; 60%) and roots (14 to 29 ng g⁻¹ FW; 107%). It also reduced malondialdehyde (17.33 to 11.4 µmol g⁻¹ FW; 34%), EL (45% to 33%; 26%), and H₂O₂ (25 to 15 µmol g⁻¹ FW; 40%) versus salt-stressed plants. DA exhibited salinity-dependent regulatory effects on diosgenin biosynthetic genes: at 150 mM NaCl + 200 µM DA, BGL and C4 reached their highest expression (19.05- and 8.84-fold), whereas at 300 mM NaCl + 200 µM DA, C26 , CAS , SEP , SMT , SQS , and SSR were maximally induced (17.83-, 18.00-, 13.66-, 11.33-, 10.66-, and 28.00-fold). These transcriptional changes culminated in the highest diosgenin content (103.33 mg g⁻¹ FW), with 390% and 209% increases over control and salinity alone. Conclusions Exogenous 200 µM DA alleviated salinity damage and promoted diosgenin biosynthesis through coordinated regulation of water status, ion homeostasis, hormonal and oxidative balance, and key biosynthetic genes. These findings highlight DA as a promising elicitor for improving salinity tolerance and diosgenin production in fenugreek, supporting future field validation and mechanistic studies.