An effective protocol has been developed for plant regeneration from cotyledon explants of Swainsona salsula Taubert (Saline swainsona), a medicinal and agronomic shrub. Adventitious shoots were obtained from 83.2% of cotyledon explants from 3-day seedlings cultured on Murashige and Skoog (MS) medium containing 2.0mgl−1 thidiazuron (TDZ), with an average of 9.3 shoots per explant. Individual elongated shoots were rooted on half strengthMS medium supplemented with 2.0mgl−1 indole-3-butyric acid (IBA), with 59.3% success. Regenerated plants with well developed shoots and roots were successfully transferred to soil, without detectable variants. Histological observation revealed that shoots developed from cotyledon explants via organogenesis, with little callus.

We have developed a reliable and high-frequency system of transformation and regeneration via somatic embryogenesis (SE) of Lycium barbarum. Leaf segments were co-cultivated with Agrobacterium tumefaciens EHA101 (pIG121Hm) carrying the neomycin phosphotransferase II gene as a selectable marker and an intron-β-glucuronidase (GUS) gene as a reporter marker. On the medium for callus-induction, which contained 50mg l-1 kanamycin (Km), approximately 60% of the explants produced kanamycin-resistant (KmR) calli. After three subcultures on the same selective medium, KmR calli were transferred onto SE induction medium containing 25mg l-1Km, where they produced numerous somatic embryos (166 g-1fresh weight callus) that subsequently developed into KmR plantlets. Compared with the untransformed control calli, the transformed calli maintained their higher frequency of SE up to 16 months after transformation. GUS staining and polymerase chain reaction and Southern blot analyses confirmed the integration of the T-DNA into the plant genome.

A micro-propagating system based on the young stem node segments of Sophora flavescens Ait. (Fabaceae) was established. Murashige and Skoog (MS) basal medium supplemented with 8.88μM 6-benzyladenine (BA) plus 2.69μM a-naphthalene acetic acid (NAA) and that with only 5.37μM NAA were found the best in promoting proliferation of shoots and induction of root, respectively. Percentages of shoot induction and number of shoot per explant were up to 93.4% and 4.2 and rooting rate to 82.4%, respectively. The segments of the regenerated shoots could be continuously induced to reproduce new shoots through subculture on the same medium in 30-d intervals and still kept this activity after being subcultured for 6 generations. After the regenerated plantlets were transplanted to field, they grew well, showing no any visible abnormalities.

Development of an efficient in vitro plantlet regeneration system from tubers of Stachys sieboldii (Miq.), a traditional Chinese medicinal plant and vegetable, is described. Adventitious shoots with an average of 9.1 (after 4 weeks of incubation) shoots per explant were obtained from 60.4% of tuber explants cultured on Murashige and Skoog (MS) medium containing 1.0mgl−1 thidiazuron (TDZ), and after another 4 weeks of incubation on growth regulator free MS medium, 33.5 shoots per explant were achieved. Subcultures showed results that were similar to those of the initial culture. Excised shoots were rooted both on MS and on half strength MS medium with a frequency of about 95%. Excised shoots were also rooted ex vitro by directly planting them into cups containing sand. Regenerated plants with well developed shoots and roots were successfully transplanted to soil, after which they developed free of abnormalities.

Great progress has been made in recent years in studies on the mechanism of Agrobacterium-mediated transformation and its application. Many details of the key molecular events within the bacterial cells involved in T-DNA transfer have been elucidated, and it is notable that some plant factors which were elusive before are purified and characterized. Vast kinds of species, which were either recalcitrant to or not included in the host range of Agrobacterium, can now be transformed by this bacterium, and they include the very important cereal species, gymnosperms, yeast and many filamentous fungi. The simple in vivo transformation of tissue in intact plants and the "agrolistic" methods to transform recalcitrant plants are the two novel technical achievements. Combined with other powerful techniques such as bacterial artificial chromosome, very large DNA fragment can be transformed into the plant genome by Agrobacterium. Further studies will elucidate more plant-encoded factors involved in T-DNA transformation and there is a need to develop more powerful Agrobacterium-based transformation systems to meet different needs in basic research and crop improvement practice.