Abstract:

Transgenic crops such as soybean and cotton have been widely planted nowadays in China. Much effort has been made to improve the quality of soybean, which is one of the main foods in China. Although transgenic legume has been put into the spotlight ever since 1984 when the first transgenic soybean was successfully obtained, setting up an effective transformation and regeneration system of soybean is still a challenge to investigators.
Cotyledon nodes from soybean seeds germinated for 5–6 d were used in Agrobacterium tumefaciens-mediated transformation system as explants to study the factors these affect the transformation rate. The explants were first infected with Agrobacterium tumefaciens strain LBA4404 containing pBI121 by 60 hours’ co-cultivation. After washed with sterile water, the explants were then put onto shoot-inducing medium containing kanamycin for selection. Then, the induced seedlings in 4–5 centimeters long were transferred onto root-inducing medium. Finally, they were transplanted into soil when the roots had formed, and identified by PCR and Southern blot.
The transformation rate was affected by three factors in this process. Hormone concentration was regarded as the most important factor in the regeneration system, so IBA as the phytohormone and 6-BA as the mitogen, with different concentrations were used to induce buds and roots formation. A relatively optimal system with 1.7 mg/L 6-BA and 0.5 mg/L IBA was acquired in which the budding percentage reached 81%.
Genotype of the soybean was regarded as the second important factor in the transformation system. Four different kinds of soybean cultivars were used to test the influences of genotypes on transformation rate. Among them, the transformation percentage of Xiaoli Dou was up to 29%, nearly one fold higher than Heinong 10. Agrobacterium tumefaciens strain LBA4404 could infect plants and transfer its gene into the plants. The process took place in the co-cultivation period. So the co-cultivation period was also important in the transformation system. 60 h co-cultivation with weak light was appropriate in our experiment, and faint mark of colonies could be seen after the co-cultivation.
Transgenic plants were more resistant to kanamycin than the untransgenic ones that could be killed on the medium with kanamycin. But high levels of kanamycin would also do harm to the transgenic ones. So, right concentration, which in our test was about 50 mg/L, was required to differentiate the transformed and untransformed plants.
In conclusion, main causes that have obvious effect on the transformation and regeneration rates are the genotype of soybean, the hormone concentration for inducing buds and the kanamycin sensitivity on inducing and livability of the buds. A relatively good genetic transformation and regeneration system is established, and with which the transformation rate can reach to 2.8%.

Key words: Soybean, Cotyledon node, Transgenic plant