Enhanced tolerance of transgenic Brassica juncea to choline confirms successful expression of the bacterial codA gene

Brassica juncea cv. Pusa Jaikisan was transformed with the codA gene for choline oxidase from Arthrobacter globiformis with an aim to introduce glycine betaine biosynthetic pathway, as it lacks any means to synthesize glycine betaine. Western blot analysis revealed the presence of choline oxidase in the protein extract from the codA transgenic lines, demonstrating that the bacterial codA gene had been successfully transcribed and translated in transgenic lines. Good activity of choline oxidase indicated its presence in fully functional form in the transformed lines. This was further confirmed by the presence of glycine betaine only in the transformed lines of B. juncea. The shoots of both wild type and transformed lines were exposed to various concentrations of choline in order to evaluate if the introduction of the codA gene in any way enhances the potential of B. juncea to tolerate high levels of choline. The growth (in terms of fresh weight and dry weight) of the shoots of transformed lines exposed to high levels of choline was significantly superior to those of wild type. Moreover, the loss in chlorophyll content and the activity of photosystem II in shoots of the transformed lines exposed to high concentration of choline were significantly lower than that observed in wild type. These results showed that shoots of B. juncea transformed with the codA gene, most probably had the potential to readily convert choline to glycine betaine. Therefore, choline tolerance can be used as an efficient marker for the identification of the lines transformed with the codA gene.