Direct somatic embryogenesis through thin cell layer culture in Panax ginseng

Direct somatic embryos were differentiated on cotyledon transverse Thin Cell Layers (tTCLs) of Panax ginseng after 9 weeks in the Murashige and Skoog basal (MS) medium containing 2,4-D (5 μM). When MS medium containing 2,4-D (5μM) was used for seedling pretreatment and for tTCLs culture, somatic embryos were observed 2 weeks earlier, i.e. after 7 weeks of culture. On the tTCLs from seedlings pretreated with 2,4-D (5μM) combined with benzyladenine and zeatin at 0.1 μM (BZ), somatic embryos were observed after 6 weeks of culture and the percentage of embryogenesis was higher (62%) than when 2,4-D was used alone for pretreatment (40%). Similar results were also obtained from pretreatment with combinations of 2,4-D (5μM) and thidiazuron (TDZ) (0.01, 0.1 μM). When a combination of 2,4-D (5μM) and BZ (0.1μM) was used both for seedling pretreatment and for tTCLs culture, both somatic embryos and shoots were observed after only 3 weeks. As the concentration of BZ increased, the percentage of somatic embryogenesis decreased but the percentage of organogenesis increased. Similar responses were obtained with a combination of 2,4-D (5μM) and TDZ (0.01μM). On the medium containing both NAA (0.3μM) and BZ (1μM), globular- and heart- stage embryos developed after 4 weeks of culture into cotyledonary-staged embryos which remained dormant after a short elongation of the embryo axis. The importance of seedling pretreatment by growth substances in enhancing somatic embryogenesis is reported.