RESUMO
The accumulation of putrescine (Put) and increased arginine decarboxylase (ADC, EC 4.1.1.19) activity levels in response to osmotic stress has been reported; however, the biological meaning of this increase remains unclear. To obtain new insights into these questions, we studied the drought response of a transgenic Lotus tenuis line that expresses the oat ADC gene, which is driven by the stress-inducible pRD29A promoter. This line contains high levels of Put with no changes in spermidine and spermine contents, even under water deficits. Our results indicate that the biochemical and morphological responses to dehydration correlate with the Put level and provide evidence that Put controls the ABA content in response to drought by modulating ABA biosynthesis at the transcriptional level.
Assuntos
Ácido Abscísico/biossíntese , Dioxigenases/metabolismo , Regulação da Expressão Gênica de Plantas , Lotus/metabolismo , Proteínas de Plantas/metabolismo , Putrescina/biossíntese , Transcrição Gênica , Arabidopsis/genética , Dioxigenases/genética , Secas , Potencial da Membrana Mitocondrial , Potenciais da Membrana , Osmose , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Raízes de Plantas/metabolismo , Caules de Planta/metabolismo , Plantas Geneticamente Modificadas , Prolina/química , Fatores de Tempo , ÁguaRESUMO
Polyamines have been globally associated to plant responses to abiotic stress. Particularly, putrescine has been related to a better response to cold and dehydration stresses. It is known that this polyamine is involved in cold tolerance, since Arabidopsis thaliana plants mutated in the key enzyme responsible for putrescine synthesis (arginine decarboxilase, ADC; EC 4.1.1.19) are more sensitive than the wild type to this stress. Although it is speculated that the over-expression of ADC genes may confer tolerance, this is hampered by pleiotropic effects arising from the constitutive expression of enzymes from the polyamine metabolism. Here, we present our work using A. thaliana transgenic plants harboring the ADC gene from oat under the control of a stress-inducible promoter (pRD29A) instead of a constitutive promoter. The transgenic lines presented in this work were more resistant to both cold and dehydration stresses, associated with a concomitant increment in endogenous putrescine levels under stress. Furthermore, the increment in putrescine upon cold treatment correlated with the induction of known stress-responsive genes, and suggested that putrescine may be directly or indirectly involved in ABA metabolism and gene expression.