Nitric Oxide Increased the Rosmarinic Acid and Essential Oil Production in In vitro-cultured Melissa officinalis

Nitric oxide is a free radical that recently has emerged as a key signaling molecule in regulating important physiological processes in plants.
In this work, sodium nitroprusside (SNP) was utilized as the donor of nitric oxide to investigate the effects of exogenous nitric oxide on essential oil, rosmarinic acid and antioxidant activity of in vitro-cultured Melissa officinalis plants.
The Plantlets were treated with different concentrations of SNP (0, 5, 10 and 20 mM) at eight leaf stages.
The results showed that SNP decreased trans-caryophyllene and other selected essential oils in M. officinalis plants, while increased most of major components of essential oils. The highest content for linalool, neral and thymol was achieved at 5, 5 and 20 mM of SNP respectively. The highest monoterpene (56.17 % v/w) and sesquiterpene content (76.01 % v/w) were achieved by 5 and 20 mM SNP, respectively. In addition, the class of essential oil compounds varied depending on the SNP concentration. Application of SNP on culture media increased rosmarinic acid production and phenolic levels, which in turn improved the antioxidant properties of the extracts.
It seems that nitric oxide elicited M. officinalis culture and increased the secondary metabolite production. This current finding open new opportunities for obtaining valuable natural antioxidants for commercial exploitation by using tissue culture systems.