Establishment of an efficient regeneration system using heading leaves of Chinese cabbage (Brassica rapa L.) and its application in genetic transformation.

To preserve and propagate valuable Chinese cabbage (Brassica rapa L.) using mature vegetative organs without seeds, we established a high efficiency regeneration system from heading leaf explants and further explored its application in genetic transformation. Our results showed that maximum shoot regeneration of cultivars ‘Beijing New No. 3’ (88.46 ± 1.65%) and ‘Chengyangqing’ (73.77 ± 1.73%) were obtained in the presence of 17.76 μM 6-benzylaminopurine (BA) and 5.37 μM α-naphthylacetic acid (NAA). The addition of silver nitrate (AgNO₃) at 11.77 μM was essential for shoot regeneration from heading leaf explants. Genotypic differences in shoot regeneration frequencies (from 47.24 ± 3.65 to 88.46 ± 1.65%) were observed amongst eight Chinese cabbage cultivars, in addition to the number of shoots per explant (from 1.31 ± 0.02 to 2.02 ± 0.05) in Murashige and Skoog medium containing 17.76 μM BA, 5.37 μM NAA and 11.77 μM AgNO₃. Low temperature (4 °C) had an effect on in vitro preservation of leafy heads with a delay in leaf wilting, and there were no significant differences in shoot induction frequency within 24 h for cultivars ‘Beijing New No. 3’ and ‘Chengyangqing’. In the genetic transformation experiments using selection with kanamycin (17.17 μM), a transformation efficiency of 0.6-1.2% was achieved, as assessed from PCR and Southern blot results. The above results suggested that the heading leaf explants can not only achieve efficient seed-independent propagation of Chinese cabbage, but also provide a feasible platform for genetic transformation. [ABSTRACT FROM AUTHOR]