Optimization of antibiotics during co-culture of Petunia hybrida leaf explants and Agrobacterium tumefaciens to increase gene transgenic efficiency

Gene transfer by the Agrobacterium tumefaciens is one of the well-known methods for the production of the transgenic plants. The success rate of this method depends on the growth of the bacteria and the regeneration of the plant explants. Among these variables, the antibiotics functioning as bacterial growth regulators have mainly inhibitory effects on the plant growth. Therefore, the introduction of a successful gene transfer method which is mediated by Agrobacterium requires the identification of an antibiotic with an inhibitory effect on the growth of the bacteria and also has a minimal effect on the regeneration of the explants and the growth of the transgenic plants. In this regard, the present research was conducted with the aim of optimizing the antibiotic used in co-culture in order to increase the transgenic yield of Petunia hybrida. For this purpose, a variety of antibiotics in different concentrations were tested.

The growth rate of A. tumefaciens in the different medium culture with two suitable pH for the bacterial growth (7) and plant growth (5.7) in the presence of 500 mg/L of the cefotaxime antibiotic as a common antibiotic for controlling bacterial growth was investigated. Sensitivity tests were run. The second experiment was conducted to investigate the effect of five different antibiotics in three concentration on the regeneration of the petunia leaf explants.

The results of the bacterial sensitivity test showed that the type and concentration of salt and the pH of the medium culture significantly affect the growth rate of the bacteria. So that the highest rate of bacterial growth was observed in LB and MH medium culture at pH=7, but on the contrary, no growth was observed in MS medium culture. In addition, two antibiotics of cefotaxime and ceftriaxone at 700 mg/L concentration had the highest inhibitory effect on the bacterial growth. The results of this experiment showed that different antibiotics have different effects on the regeneration of explants and the growth of the seedlings. According to the results, the highest volume of callus and also the highest percentage of regeneration were observed in the presence of ceftizoxime and coamoxiclav antibiotics in all three concentrations and cefepime at 300 mg/L. The highest number of the seedlings was also observed in the treatment of ceftizoxime at concentrations of 300 and 500 mg/L with an average of 7.70 seedlings. In relation to the seedling growth traits, the highest number and length of root per seedling were observed in ceftizoxime at 300 mg/l and cefotaxime at the same concentration, respectively. The highest dry weight belonged to the grown seedlings in the presence of co-amoxiclav antibiotic followed by the ceftizoxime (300 mg/L).

 The overall results of these experiments show that the seedlings which are grown in the presence of ceftizoxime antibiotic had a good growth rate, while the use of this antibiotic was effective in inhibiting the growth of A. tumefaciens. Therefore, we recommend that the use of ceftizoxime antibiotic in the co-culture process will be effective in increasing the efficiency of the gene transfer. Further studies will solidify these results.