Effect of 6-BA and 2,4-D concentrations in the proliferation medium on growth intensity and transformation efficiency. All the 6-BA concentrations were tested in the presence of 4.52 μM 2,4-D and all the 2,4-D concentrations were tested in the presence of 12 μM 6-BA. Callus growth was measured by the difference between the final and initial weight of embryogenic cultures after a 4 week proliferation cycle. The initial weight was calibrated at 120 ± 10 mg. Each datum corresponds to the mean ± SD of 4 measurements. Confidence interval is indicated by vertical bars. We performed an ANOVA followed by the Tukey HSD test to identify significant differences between the means of all treatments. Values with different letters are significantly different at P ≤ 0.05. Transformation efficiency was assessed by observing GFP epifluorescence 6 weeks after the end of co-cultivation. Transformation efficiency was analyzed by the proportion (p) of transformed calli (p = x/n), where x was the number of transformed calli and n the number of co-cultivated calli. A 3 δ confidence limit for binomial distribution was calculated using the formula with a level of confidence of 99%. All the transformation experiments were conducted independently in four replicates each comprising 60 calli (240 calli/ hormonal combination).