Inducible overexpression of oat arginine decarboxylase in transgenic tobacco plants.

To test the possible interaction of polyamines in plant growth responses, transgenic tobacco plants containing the Avena sativa L. (oat) arginine decarboxylase (ADC) gene under the control of a tetracycline-inducible 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 during vegetative stage, displayed different degrees of an altered phenotype, the severity of which was correlated with putrescine content. These phenotypic changes were characterized by short internodes, thin stems and leaves, leaf chlorosis and necrosis, as well as reduced root growth. This is the first report to show altered phenotypes as a consequence of polyamine changes under tetracycline-induction in in vivo conditions. Interestingly, overexpression of oat ADC in tobacco resulted in similar detrimental effects to those observed by ADC activation induced by osmotic stress in the homologous oat leaf system. In the context of the role of specific polyamines in plant growth and development, the present results indicate that activation of the ADC pathway leading to high levels of endogenous putrescine (or its catabolytes) is toxic for the vegetative growth of the plant. In contrast, no visible phenotypic effects were observed in flowering plants following tetracycline induction. Further characterization of the different transgenic lines may shed light on the action of specific polyamines in different plant developmental processes.