Effects of nitric oxide applications on biosynthesis pathway of phenolic compounds in common sage (Salvia officinalis L.) plant

Nitric oxide (NO) is a key signaling molecule involved in various physiological processes in plants, including growth, development, and stress responses. In recent years, there has been growing interest in understanding the role of NO in enhancing the accumulation of phenolic substances and antioxidant capacity in plants, particularly in medicinal herbs such as Salvia officinalis. Therefore, in this study, the effect of exogenous NO applications on phenolic and flavonoid content, antioxidant capacity and phenolic acid composition, as well as the expression of some important genes involved in the synthesis of phenolic compounds in S. officinalis leaves was evaluated. S. officinalis leaves were foliar sprayed with 0, 100, and 1000 M NO donor diethylenetriamine NONOate. The leaf samples were harvested after 24 hours of the last treatment for analyses. Exogenous NO tretment resulted in an increase of total phenolic and flavonoid content. The antioxidant capacities of extracts was tested through complementary methods (total antioxidant capacity (TAC), 1,1-diphenyl-2-picrylhydrazyl (DPPH) antiradical capacity, cupric ion reducing antioxidant capacity (CUPRAC) and ferric ion reducing antioxidant potential (FRAP)], and the application of NO considerably enhanced the antioxidant activity. HPLC analysis revealed the presence of rosmarinic acid as the main compound in the extracts, and 100 mM NO application increased the content of ferulic and rosmarinic acids. The expression levels of the key genes (PAL, C4H, 4CL, TAT, HPPR, and RAS) involved in the both phenylpropanoid and tyrosine-derived pathways were affected by exogenous NO application. Our findings show that the increase in PAL, TAT and RAS expression levels in leaf tissues of S. officinalis after NO application is associated with phenolic acid content and antioxidant capacity.