INCREASED PUTRESCINE BIOSYNTHESIS THROUGH TRANSFER OF MOUSE ORNITHINEDECARBOXYLASE CDNA IN CARROT PROMOTES SOMATIC EMBRYOGENESIS

Carrot (Daucus carota L.) cells were transformed with Agrobacterium tu mefaciens strains containing 3'-truncated mouse ornithine decarboxylas e (ODC) cDNA under the control of a cauliflower mosaic virus 35S promo ter. A neomycin phosphotransferase gene linked with a nopaline synthas e promoter was used to select transformed cell lines on kanamycin. Alt hough the nontransformed cells contained no ODC, high amounts of mouse -specific ODC activity were observed in the transformed cells. Transge nic cells showed a significant increase in the cellular content of put rescine compared to control cells. Spermidine, however, remained unaff ected. Not only did the transformed cells exhibit improved somatic emb ryogenesis in the auxin-free medium, they also regenerated some embryo s in the presence of inhibitory concentrations of 2,4-dichlorophenoxya cetic acid. These cells acquired tolerance to alpha-difluoromethylargi nine (a potent inhibitor of arginine decarboxylase) at concentrations that inhibit growth as well as embryogenesis in nontransformed carrot cells, showing that the mouse ODC can replace the carrot arginine deca rboxylase for putrescine biosynthesis in the transgenic cells.