    4.1.1.50 | cDNA of Datura stramonium is introduced in Nicotiana tabacum L. cv. Xanthi in antisense orientation under the CaMV 35S promoter, by means of Agrobacterium tumefaciens and leaf disc transformation. Primary transformants efficiently transcribe the antisense SAMDC gene, but SAMDC activity and PA titers do not change. By contrast, in most transgenic shoots of the second generation, SAMDC activity is remarkably lower than in controls, and the putrescine-to-spermidine ratio is altered, mainly due to increased putrescine, even though putrescine oxidising activity (diamine oxidase, EC 1.4.3.6) does not change relative to controls. Despite the reduction in SAMDC activity, the production of ethylene, which shares with PAs the common precursor SAM, is not influenced by the foreign gene. Some plants are transferred to pots and acclimatised in a growth chamber. In these in vivo-grown second generation transgenic plants, at the vegetative stage, SAMDC activity is scarcely reduced, and PA titres do not change. Finally, the rhizogenic potential of in vitro-cultured leaf explants excised from antisense plants is significantly diminished as compared with WTones, and the response to methyl jasmonate, a stress-mimicking compound, in terms of PA conjugation, is higher and differentially affected in transgenic leaf discs relative to WT ones |
