Medicinal plants play vital roles in treatment and preventioof disease. Hypericum perforatumL. (St. John’s wort) is a well-known medicinal plant that has been in use for a decade. The antidepressant properties ofHypericumhas become demonstrated.The antidepressant role of Hypericumis related to hypericin, pseudohypericin, protohypericin, protopseudohypericin and Hyperforin which exclusively produced in Hypericum. The concentration of hypericin and pseudohypericin in extraction of Hypericum not only is low, but the amount of those in winter and summer are different. Tissue culture technique is a way to solve of this limitation. In order to increase of Hyperforin in adventitious root of Hypericum extract, various concentration of silver nitrate (15, 30, 45 and 60 micromolar), polyethylene glycol (0.25, 0.5, 0.75, 1, 1.5 and 2 %) and methionine (25, 50, 100, 150 and 200 mg/l) were used. The results of analysis of variance have shown that the various treatments had different effect on amount of Hyperforin. The silver nitrate at concentration of 15 micromolar at the first week and the concentrations of 30 and 45 micromolar at second week had most effect on the amount of Hyperforin. Other treatments had not significant effect. At the second week, silver nitrate (15 and 60 micromolar) and methionine (200 mg/l) increase the amount of Hyperforin (2899.18, 3073.85 and 2504.86 respectively). The comparison various concentration of silver nitrate showed that the concentrations of 15 and 30 micromolar had the most effect on the expression of PKS1 gene (17.34 and 20.01 respectively). Although the silver nitrate at the concentration of 45 micromolar increased the expression of gen, but this increase not significant. Key words : Hyperforin, Hypericum perforatumL., silver nitrate, polyethylene glycol
