The effect of silicon application and salicylic acid on enzymatic and non-enzymatic reactions of Scophularia striata L. under drought stress

Foliar spraying of salicylic acid (SA) and silicon (Si) was carried out as a moderator of drought stress on growth and antioxidant system in two different ecotypes of scrophularia striata as a medicinal plant. A factorial experiment was conducted based on a completely randomized design in three replications. The statistical analysis of the studied traits showed that drought stress decreased the length and weight (dry and fresh) traits of shoot, root and stem-to-root length ratio in Ilam ecotype, while the root length and root-to-stem length ratio increased in Abdanan ecotype. The interaction between salicylic acid (SA), silicon (Si) and drought stress caused an increase in root length and the root-to-stem length ratio in Abadanan ecotype, this interaction on root fresh weight was not significant. The application of drought stress led to a reduction in the content of total phenol, flavonoid, anthocyanin and ascorbic acid in both ecotypes, but the activity of ascorbate peroxidase (APX) enzyme increased in both ecotypes and polyphenol oxidase (PPO) in Ilam ecotype. The interaction between salicylic acid (SA), silicon (Si) and drought stress increased the enzyme antioxidant activity, catalase (CAT), guaiacol peroxide (GPX), as well as the content of flavonoid, ascorbic acid and phenol in Ilam ecotype (50% field capacity +drought stress) and Abdanan ecotype (50% field capacity). However, this interaction had no significant effect on the activity of ascorbate peroxidase (APX) enzyme. The general results showed that the simultaneous use of SA and Si improves the antioxidant defense in Scrophularia striata under drought stress.