Efficient transformation of beet (Beta vulgaris) and production of plants with improved salt-tolerance

Small bud tips of 1-3 mm in length were taken from multiple shoot clumps that derived from immature inflorescence cultures of beet as recipient for the Agrobacterium-mediated transformation and transgenic plants were obtained from eight genotypes. The optimal genetic transformation protocol was established as followed: the buds were immersed in Agrobacterium suspension of OD600 =0.3-0.5 for 5-10 min, with vacuum infiltration (0.3-0.5 x 10(5) Pa) or supplemented with 0.01% Silwet L-77, co-cultured for 2-4 days and followed by 10-day culture on medium containing 100 mg l(-1) cefotaxime, then the buds were selected on medium containing 10 mg l(-1) hygromycin B for three consecutive generations. The percentage of hygromycin-resistant buds after three selections varied from 13.3 to 30.6% with genotypes. The results of PCR and further Southern blotting of genomic DNA of hygromycin-resistant buds or plants showed that the exogenous hpt and AtNHX1 gene had been integrated into the genomes of some transformed buds or plants. The transgenic buds or plants with AtNHX1 gene encoding Na+/H+ antiport on the vacuole membrane of Arabidopsis showed improved salt-tolerance than the controls. AtNHX1gene inherited in some transgenic lines as Mendelian segregation. This result revealed that it was feasible to improve salt-tolerance of beets by the introduction of AtNHX1 gene into cultured buds.