Sodium nitroprusside mediated defense networks for genotype-specific drought adaptation in walnut

Abstract

This study explored the interactive effects of sodium nitroprusside (SNP) and drought stress on the physiological and biochemical responses of four walnut (Juglans regia L.) genotypes: ‘Chandler’, ‘Fernor’, ‘Howard’, and the local ‘Rayen’. A factorial completely randomized design (CRD) was conducted with three fixed factors (genotype, SNP treatment, and irrigation regime); plants were treated with 200 µM SNP, selected based on preliminary assays, alongside an untreated control, two irrigation regimes (well-watered and water-stressed). The experimental unit was an individual pot containing one seedling, with six independent experimental units per treatment combination (Three replications × two pots). Data were analyzed using three-way factorial ANOVA including all main effects and two-way and three-way interactions (G × S, G × I, S × I, and G × S × I), with normality and homogeneity of variance verified prior to analysis. Under water deficit, foliar SNP application (200 µM) significantly reduced malondialdehyde (MDA) accumulation, across all genotypes (e.g., Chandler: 0.70 to 0.35 nmol/g), though a slight MDA increase was observed under well-watered conditions, indicating contextdependent oxidative effects. SNP treatment was also associated with significantly increased catalase and peroxidase activities, elevated proline and soluble sugar contents, and better preserved chlorophyll and carotenoid levels, collectively indicating enhanced osmoprotection photosynthetic stability and improve tolerance under stress. Principle component analysis revealed genotype-specific multivariate physiological shifts; 'Howard' exhibited the strongest PC1 shift under drought (+4.324), primarily associated with chlorophyll preservation, and whereas 'Chandler', 'Fernor', and 'Rayen' showed more pronounced SNP responses under well-watered conditions. These PC1 shifts reflect multivariate physiological changes and should not be interpreted as direct effect size quantifications. Collectively, these findings suggest that SNP can mitigate drought induced oxidative and osmotic damage, in a genotype- and condition-dependent manner highlighting its potential as a biochemical priming agent for enhancing stress resilience in walnut.