| Soil salinity is a severe global problem, nearly 10% of the total land surface is coved with different types of salt affected soils. To improve plant salt-tolerance is one of main breeding goals. Conventional forest breeding is constrained by its long reproductive cycle, which includes long juvenile period, and by its complex reproductive characteristics, such as self-incompatibility and a high degree of heterozygosis. Gene transformation has played an important role in woody plant improvement, which can shorten breeding period and breed varieties with high salt tolerance.Chinese sweetgum is an important woody species while it is a few study on its tissue culture and transformation. Refer to the advance in tree tissue culture, especially that of American sweetgum, we analyzed factors affecting efficiency of Chinese sweetgum tissue culture and set up its culture system. The results showed that 1/2MS is the best medium for callus induction, and hypocotyls is the best explant for callus induction, 1/2MS basal medium with 3．0mg.L-1 6-BA and 0．5 mg.L-1 NAA and that with 6-BA 1．0 mg.L-1 and NAA 0．1 mg.L-1 were the optimum media for callus induction and shoot regeneration respectively. Adventitious buds of Chinese sweetgum were very easy to rootting on WPM basal medium with 2．0 mg.L-1 IBA in 2 weeks.It is found that Chinese sweetgum is sensitive to kanamycin, explants died after 2 w on medium with 25 mg.L-1 kanamycin. Five times of usual concentraton of Agrobacterium was suitable for gene transformation because the transformation rate was higher than other concentrations did, and Agrobacterium growth could be suppressed by cefotaxime in the continuative selection and regeneration media.Usually a functional gene in the vector is driven by a constitutive promoter such as 35S promoter from CaMV that is active in all tissue, and expressed during different growth phase. In order to save energy we tried to construct a vector driven by an inducible promoter. Rd29A promoter, an inducible one, is able to direct osmotic gene expression when plant was exposed to salt, cold and drought stress, with the advantage that expression was absent or undetectable in natural growth phase. This could minimize or avoid unnecessary expression in non-target plant tissues. Primers for PCR amplification of Rd29A promoter were designed and synthesized based on the information of Genbank, and used for Rd29A promoter amplificated from Arabidopsis genomic DNA, A plasmid named pBinRd29A which contained this promoter, BADH gene andΩenhancer, was constructed and used for transformation mediated by Agrobacterium tumefaciens. We get 17 and 28 putative transgenic plants from Chinese sweetgum and tobacco respectively. PCR analyses confirmed the presence of the Rd29A promoter in transgenic sweetgum genomes. The transgenic tobacco plants growth normal until flowering and setting seeds, except that their leafy brims were curl. Resistance to kanamycin was analyzed in a T line of tobacco, the results suggested that foreign gene was inserted in one locus of plant genome. It's not significantly different in seed germination rate under NaCl stress from 0．2% to 0．8% (W/v), but the root significantly shorter than the control, the result indicated that foreign gene enhanced salt tolerance of transgenic plant. |
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