ZnO-NPs and SA Synergistically Boost Physiological and Molecular Adaptive Responses to Salt Stress in Greengram

This study reported the synergistic role of zinc oxide nanoparticles (ZnO-NPs; 100 mg L^-1) and salicylic acid (SA; 0.2 mM) in mitigating the adverse effects of salinity (NaCl) stress in greengram. The combined (ZnO-NPs + SA) treatment improves diverse morphological, physiological, and biochemical traits in greengram during salt stress. For instance, ZnO-NPs + SA treatment increased root biomass (40.6%), chlorophyll a (25%), and carotenoid contents (31.5%) under 50 mM NaCl stress. ZnO-NPs + SA also showed a remarkable reduction in hydrogen peroxide (67.7%) and lipid peroxidation (68.7%), indicating improved redox stability. Notably, the combined treatment restored ion homeostasis by reducing Na⁺ accumulation in roots and shoots by 76.3% and 69.7%, and enhancing K⁺ levels by 56.2% and 54%, in greengram at 50 mM NaCl concentration. Additionally, ZnO-NPs + SA treatment improved the antioxidant defense responses in salt-stressed greengram, as seen by the increased accumulation of enzymes such as CAT, APX, GPOX, SOD, and GR and their expression. The combined treatment further boosted the non-enzymatic antioxidants, including PAL, TAL activity, total phenol, flavonoids, DPPH and FRAP in salinity-stressed greengram plants. The synergistic nanoparticle-phytohormone interaction improved the yield attributes of salinity-stressed greengram, underscoring its agronomic value. Overall, the current study reveals a novel, integrated physiological-molecular mechanism by which ZnO-NPs and SA jointly enhance salinity tolerance, offering a promising strategy for cultivating greengram and other legumes in salt-affected soils. These findings provide a practical, scalable bio-stimulant strategy for improving legume productivity in salinity-affected agricultural systems.