Objective: Dracocephalum kotschyi Boiss. has medicinal properties due to its valuable compounds. The aim of this study was to investigate the effects of red or blue light and sodium nitroprusside (SNP) on enhancing secondary metabolites in D. kotschyi

Method: Seven-day-old seedlings treated under white and red-blue combined spectrum, and were irrigated with Hoagland's solution. After five weeks, half of the plants were harvested, while the others were subjected to SNP treatment at concentrations of 0, 0.5, and 1 µM. The experiments were conducted in three replicates using a completely randomized block design, and data were analyzed using one-way analysis of variance.

Results: Under blue light and in the absence of SNP, the levels of H₂O₂ and MDA of the plants were lower than those in samples grown under white light. Under both white and blue light, SNP application, in a concentration-dependent manner, reduced pigment contents while increasing peroxidase and phenylalanine ammonia-lyase activities. Additionally, accumulation of proline, polysaccharides, phenolic compounds, and flavonoids was observed. Under white light, chlorophyll b content, reducing sugars, polysaccharides, and superoxide dismutase activity increased in the presence of SNP. Red-blue light (at a 1:1 ratio) treatment resulted in increased chlorophyll and carotenoid contents, along with decreased levels of H₂O₂, proline, reducing sugars, polysaccharides, phenolic compounds, flavonoids, and reduced activities of antioxidant enzymes and PAL, even in the presence of SNP.

Conclusions: Cultivation of D. kotschyi under blue light together with SNP enhanced secondary metabolite content by activating the plant's antioxidant defense system, PAL, and modulating carbon metabolism.