INDUCIBLE OVEREXPRESSION OF OAT ARGININE DECARBOXYLASE IN TRANSGENIC TOBACCO PLANTS

To test the possible interaction of polyamines in plant growth respons es, transgenic tobacco plants containing the Avena sativa L. (oat) arg inine decarboxylase (ADC) gene under the control of a tetracycline-ind ucible promoter were generated. Inducible overexpression of oat ADC in transgenic tobacco led to an accumulation of ADC mRNA, increased ADC activity and changes in polyamine levels. Transgenic lines, induced du ring vegetative stage, displayed different degrees of an altered pheno type, the severity of which was correlated with putrescine content. Th ese phenotypic changes were characterized by short internodes, thin st ems and leaves, leaf chlorosis and necrosis, as well as reduced root g rowth. This is the first report to show altered phenotypes as a conseq uence of polyamine changes under tetracycline-induction in in vivo con ditions. Interestingly, overexpression of oat ADC in tobacco resulted in similar detrimental effects to those observed by ADC activation ind uced by osmotic stress in the homologous oat leaf system. In the conte xt of the role of specific polyamines in plant growth and development, the present results indicate that activation of the ADC pathway leadi ng to high levels of endogenous putrescine (Or its catabolytes) is tox ic for the vegetative growth of the plant. In contrast, no visible phe notypic effects were observed in flowering plants following tetracycli ne induction. Further characterization of the different transgenic lin es may shed light on the action of specific polyamines in different pl ant developmental processes.