Melissa offisinalis is a medicinal plant belonging to the Lamiaceae family. This plant has a lot of economic significance. Tension is an important factor in determining the chemical composition and therapeutic activity of medicinal plants. When applied in a very low amount to a live system, it improves biosynthesis of certain compounds that play an important role in adapting plants to stressful conditions. One of the main ingredients in the lemon balm extract is Rosmarinic Acid. It is known that the herbal properties of this plant are related to this active ingredient.In this study, the effect of various concentrations of cadmium chloride (0.10, 20 and 40 mM) on the Rosmarinic acid content of two months old seedlings was investigated. In this study, the stems of lemon balm are in sterile conditions was propagation on the medium ½(MS) was used. After 60 days, seedlings were removed from solid MS medium, the roots were cutting and cultured in liquid medium of MS 1/2 with different concentrations of cadmium. The cultivation was carried out in erlen( 250 cc) and was kept in an incubator shaker device. After one week of growth of the stems in the medium, sampling was done for the experiment. A comparison between mean of data showed that cadmium concentrations had a significant effect on rosmarinic acid content. In all concentrations, Rosemarinic acid was significantly increased to control, so that the maximum amount of this active ingredient was at 40 μm concentration(1/5,1/9 and 2/4 fold). It seems that increasing the content of rosmarinic acid in seedlings treated with cadmium chloride is due to the activation of the involved genes in its biosynthesis.
