Effect of Rhizospheric application of NO on soil characteristics and functional attributes of Spinacia oleracea grown in untreated wastewater irrigated soil of Lohta Varanasi

Abstract

Aims: Heavy metal contamination in soils poses a serious threat to crop health and productivity, necessitating eco-friendly mitigation approaches. This study investigates the potential of nitric oxide (NO), applied as sodium nitroprusside (SNP), as an exogenous agent to alleviate metal-induced toxicity in Spinacia oleracea. It evaluates NO’s role in regulating metal accumulation, oxidative stress, and overall plant performance. Method: NO was applied at five concentrations (10, 50, 100, 200, and 500 µM) in the rhizospheric zone of metal-contaminated soil for growing spinach plants. Untreated contaminated soil served as the control. Physiological attributes such as oxidative biomarkers [hydrogen peroxide (H₂O₂), superoxide radicals (SOR), and malondialdehyde (MDA) content], antioxidant enzyme activities [superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)], and leaf surface morphology using scanning electron microscopy (SEM) were assessed. High-resolution mass spectrometry (HRMS) was used to quantify metabolite profiles to find out their role in regulating metal toxicity. Results: Among all treatments, 100 µM NO was found to be most effective, significantly enhanced biomass and reduced levels of H₂O₂, SOR, and MDA. A concurrent reduction in SOD, POD, and CAT activities indicated alleviated oxidative stress. SEM analysis showed improved leaf surface integrity, and HRMS confirmed better metabolic balance and reduced metal ion concentrations in the plant parts. Conclusion: Application of NO at 100 µM will be able to mitigate heavy metal toxicity, for enhancing physiological performance and growth of S. oleracea. This approach offers a promising and sustainable strategy for improving crop productivity in metal-contaminated soils. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.