Thiourea priming promotes coordinated redox, osmotic and ionic adjustments associated with improved salt tolerance in Vigna radiata (L.) R. Wilczek

Abstract

Soil salinity adversely affects seed germination, growth, photosynthetic performance, ionic balance, and antioxidant capacity, thereby limiting crop productivity. The present study investigated the effectiveness of seed priming treatments in improving salinity tolerance in two contrasting Mungbean (Vigna radiata (L.) R. Wilczek) genotypes, PKU-AKM 12-28 (salt-tolerant) and VBN(Gg)3 (salt-susceptible). Multiple chemical priming agents were initially screened using salt tolerance indices and principal component analysis (PCA) to identify the most effective treatment. Thiourea (TU; 1000 ppm) was identified as the most effective priming treatment and was subsequently evaluated for its effects on physiological, biochemical, antioxidant, ionic, and metabolite responses under salinity stress. Salinity significantly reduced germination, seedling growth, photosynthetic pigments, osmolyte accumulation, antioxidant capacity, and K⁺/Na⁺ ratio, while increasing lipid peroxidation. Thiourea priming substantially improved chlorophyll and carotenoid contents, enhanced accumulation of proline, soluble sugars, total free amino acids, phenolics, and flavonoids, increased catalase and peroxidase activities, and reduced malondialdehyde accumulation in both genotypes. Thiourea-treated seedlings also maintained improved ionic balance through enhanced K⁺ retention and reduced Na⁺ accumulation under salinity stress. Correlation, path coefficient, and regression analyses revealed significant statistical associations among osmolyte-related traits, antioxidant parameters, photosynthetic pigments, and biomass-related attributes. Untargeted LC-MS profiling of the susceptible genotype further revealed treatment-associated differences in metabolite composition, including amino acids, flavonoids, terpenoids, fatty acids, and other stress-associated metabolite classes. Overall, these findings indicate that thiourea priming is associated with coordinated physiological, biochemical, ionic, and metabolic adaptations that contribute to improved salinity tolerance in Mungbean seedlings.