Over expression of mitochondrial citrate synthase gene improves the growth of carrot cells in Al-phosphate medium.

A mitochondrial citrate synthase (CS) of Arabidopsis thaliana was introduced into carrot (Daucus carota L. cv. MS Yonsun) cells by Agrobacterium tumefaciens-mediated transformation. Transgenic cell lines had high CS activity, the highest value observed was 0.24 mumol (mg protein)-1 min-1 which was 1.9-fold of that in wild-type cells. Transcript levels of DcCS were similar between transgenic lines, but those of AtCS were increased as the CS activity of cells was increased. Isoelectric focussing revealed that the CS polypeptide of the transgenic lines had a pI value different from that of the wild-type cells, although the molecular mass was the same. These results indicate that the CS polypeptides of A. thaliana were expressed and processed to the mature form in carrot cells. The growth rate and excretion was 2.2-2.8 and 2.8-4.0 fold greater in the transgenic cells than in the wild type cells, respectively. Phosphate uptake from Al-phosphate also increased in transgenic cells. It appears, the overexpression of mitochondrial citrate synthase in carrot cells improves the growth rate in Al-phosphate medium possibly as a result of increased citrate excretion.