241 Effects of Growth Regulators and Explants on Callus Induction and Organogenesis in Hypericum perforatum I. Sharifi, M.H. Fotokian, A. Kordenaeij and S. Ramazani College of Agriculture and Medicinal Plant Research Center, Shahed University Tehran Iran T. Hasanlu, S.M. Khayyam Nikoei, D. Davoodi and B. Nakhoda Agricultural Biotechnology Research Institute Karaj Iran G. Mohammadinejad College of Agriculture Shahid Bahonar University Kerman Iran Keywords: BAP, IAA, MS medium, root induction, shoot induction Abstract Hypericum perforatum is a traditional medicinal plant that has been used for the treatment of neurological disorders and depression. In this research, the effect of different levels of growth regulators (IAA and BAP) and explants type (root, stem, leaf) on callus induction and organogenesis of Hypericum perforatum were studied through factorial experiment design based on completely randomized arrangement with five replications and five samples per experimental unit. Explants from sterilized seedlings were cultured on MS medium containing different concentrations of IAA (0.0, 0.5, 1.0, and 2.0 mg L -1 ) and BAP (0.0, 0.4, and 0.8 mg L -1 ). We incubated the samples in the dark at 23°C for 28 days. After this period, variables including callus size, number of roots and number of shoots were measured. Among tested explants, leaf explants was found to be most effective as it produced the most number of roots and shoots. The main effects of IAA and BAP and also the interaction or combination effects of these growth regulators were statistically significant (P≤0.01) on all traits. The maximum number of shoots was obtained in leaf explants, when the concentration of BAP and IAA was high and low, respectively. Our findings are compatible with the results reported that in H. perforatum, BAP was found to be the most efficient in promoting shoot regeneration when leaves were used as the explants. INTRODUCTION Medicinal plants are the most important source of life saving drugs for the majority of the world’s population. The biotechnological tools are important to select, multiply and conserve the critical genotypes of medicinal plants. In-vitro regeneration holds tremendous potential for the production of high-quality plant-based medicine. St. John’s wort (Hypericum perforatum L.) is a well-known traditional medicinal plant that has been used for centuries for the treatment of several diseases, such as skin lesions, eczema, cancer, burns and microbial, inflammatory, anti-oxidant and psychological disorders (Dias et al., 1998; Ishiguro et al., 1998; Barnes et al., 2001; Sanchez-Mateo et al., 2002; Agostinis et al., 2002; Silva et al., 2005). In vitro systems have been reported as an effective tool for obtaining genetically uniform plants, which can be a source of variable pharmaceutical preparations (Santarem and Astarita, 2003). Plant regeneration of the Hypericum species has been achieved by using as explants the whole seedling or their excised parts (Cellarova et al., 1992; Bernardi et al., 2007; Ayan and Cirak, 2008; Namli et al., 2009; Namli et al., 2010), hypocotyl sections (Murch et al., 2002; Zobayed et al., 2004), leaves (Pretto and Santarem, 2000), leaf discs and stem segments (Ayan et al., 2005), and adventitious roots Proc. IS on Medicinal and Aromatic Plants Eds.: N. Chomchalow et al. Acta Hort. 1023, ISHS 2014