Effect of silver nanoparticles on growth indicators and antioxidant properties of Melissa officinalis L in invitro culture conditions

Lemon balm (Melissa officinalis) is a medicinal plant belonging to lamiaceae and is rich in antioxidant compounds. with the aim of optimizing the production of antioxidant compounds, in this research, we studied the effect of different concentrations of silver nanoparticles on growth indices and antioxidant activity of proliferated shoots in vitro culture. For this purpose, seedlings of seed germination in MS medium were transferred for propagation to MS culture medium containing 1 mg / l BAP and 0.5 mg / l NAA. after one month, silver nanoparticles with concentrations of 0, 1, 2, 3 and 4 ppm were added to the culture medium  and growth indices, antioxidant activity by free radical scavenging (DPPH), reducing power (RP) and superoxide anion scavenging activity (SOD) and phenolic and flavonoid compounds compositions of the proliferated shoots at 14 and 28 days intervals were measured after treatment. The results of growth analysis showed that increasing the concentration of silver nanoparticles from 1 to 4 ppm increased growth indices (fresh and dry weight of the plant, shoot and root length, number of leaves and number of shoots). This increase was evident 28 days after treatment. The number of leaves and the number of brancheswere affected more than other indices. The lowest amount of IC50, the highest activity reducing power activity (RP) and superoxide anion scavenging activity (SOD), and the highest amount of phenoli and flavonoid compounds were observed in the treated shoots with a concentration of 1 μg / ml silver nanoparticles for 28 days. Generally higher concentrations of silver nanoparticles for growth indices and its lower concentration is suggested to be useful for the production of antioxidant compounds.