Effect of salicylic acid and silicon on physiological parameters and anatomical index of Scrophularia striata L. under drought stress

) on the physiological, anatomical, and phytochemical responses of Scrophularia striata roots in two ecotypes (Ilam and Abdanan) under greenhouse conditions. A factorial experiment based on a completely randomized design with three replications was employed. Results showed that drought stress significantly reduced chlorophyll content, relative water content (RWC), total protein levels, and anatomical traits including (xylem vessel diameter and phloem vessel diameter), while increasing ion accumulation. However, foliar application of Si enhnaced antioxidant activity, as measured by the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay, in addition, SA and Si treatments under drought stress enhanced chlorophyll b, carotenoid content, RWC, and total protein, accompanied by modifications in vascular tissues structure. GC-MS analysis revealed that drought stress alone decreased both the number and diversity of secondary metabolites in both ecotypes. In contrast, the application of SA and/or Si under drought conditions induced treatment- and ecotype-specific alterations in metabolite composition, characterized by changes in the relative abundance of major metabolite classes and the emergence of specific compounds, rather than a uniform increase in total metabolite content. Furthermore, the combined application of SA and Si resulted in additional modifications of the phytochemical profile, indicating qualitative metabolic reprogramming. Overall, these findings demonstrate that the phytochemical responses of Scrophuralia striata to drought stress are primarily governed by interactions between drought stress and elicitor treatments, highlighting the modulatory role of SA and Si in enhancing plant adaptation to drought stress.