Somatic embryogenesis and shoot organogenesis from leaf explants of Primulina tabacum

Primulina tabacum is a rare and endangered species that is endemic to China. Establishing an efficient regeneration system is necessary for its conservation and reintroduction. In this study, when leaf explants collected from plants grown in four ecotypes in China are incubated on Murashige and Skoog (MS) medium containing 5.0 mu M thidiazuron (TDZ) for 30 days, then transferred to medium containing 5.0 mu M 6-benzyladenine (BA), adventitious shoots are then observed. Conversely, when leaf explants are incubated on medium containing 5.0 mu M BA for 30 days, then transferred to medium containing 5.0 mu M TDZ, somatic embryogenesis is induced. This indicates that somatic embryogenesis and shoot organogenesis could be switched simply by changing the order of two cytokinins supplemented in the culture medium. Histological investigation has revealed that embryogenic cells are induced within 30 days following incubation of explants in medium containing TDZ. Only if embryogenic cells were induced, TDZ could enhance somatic embryogenesis and BA could stimulate shoot organogenesis. When comparing explants from different ecotypes, leaf explants from Zixiadong in Hunan Province could induce low numbers (1-2) of either somatic embryos or adventitious shoots on medium containing either 5.0 mu M TDZ or 5.0 mu M BA, respectively. Whereas, leaf explants from plants collected from the other three ecological habitats could induce 50-70 somatic embryos/adventitious shoots per explant. Moreover, somatic embryos could induce secondary somatic embryogenesis and adventitious shoots on different media. All regenerated shoots developed adventitious roots when these are transferred to rooting medium, and over 95% of plantlets have survived following acclimatization and transfer to a potting mixture (1: 1, sand: vermiculite).