Urra Rodríguez, Marina2018-08-132023-07-012018https://academica-e.unavarra.es/handle/2454/29748Crop productivity relies heavily on fertilization. However, the augmented use of fertilizers by industrial farming results in an over-accumulation of nutrients in the soil, which induces nutritional stresses. The utilization of nitrate, ammonium, and urea as nitrogen sources leads to an elevated intracellular accumulation of ammonium, which makes indispensable to understand and elucidate the mechanism by which plants face ammonium toxicity. Early studies on plant metabolism of polyamines pointed to their involvement in responses to different environmental stresses. However, the precise mechanisms by which polyamines control plant responses to stress stimuli have not been elucidated yet. Previous results of our laboratory suggested the importance of the “urea cycle” on the tolerance of Medicago truncatula seedlings to ammonium, in which polyamine catabolism might play a key role in such tolerance, but there are still important gaps to fulfill. The excess of ammonium originated either from ammonium nutrition or from polyamine metabolism may be suggested to act as a feedback inhibitor of amine oxidases since polyamines, mainly putrescine, were accumulated while the content of γaminobutyric acid decreased. In the present study, an intra- and interspecific phylogenetic analyses of amine oxidases are performed in order to characterize them. Moreover, the differential effect of distinct nitrogen nutrition and doses on diamine oxidases and polyamine oxidases activities involved in the catabolic processes of polyamines in connection to the “urea cycle” was assayed. In general terms, the results obtained in this study showed higher diamine oxidase activities in Medicago truncatula plant shoots than that observed in roots. In addition, plants supplied with low dose of ammonium exhibited significantly higher diamine oxidase activity in shoots in comparison with nitrate- and urea-fed plants, whereas diamine oxidase activity was significantly higher in roots of ammonium-fed plants at high dose. Since diamine oxidase activity has been shown to be increased under ammonium conditions in Medicago truncatula tissues, this might suggest the importance of polyamine catabolism in the tolerance against high ammonium conditions. Although alternative mechanisms underlying ammonium stress/tolerance response are proposed in this report, future research should be performed to elucidate the mechanisms underlying plant ammonium tolerance responses.application/pdfengMedicago truncatulaAmine oxidasesPolyaminesDiamine oxidaseNitrogenAmmoniuminfo:eu-repo/semantics/bachelorThesis2018-06-28Acceso abierto / Sarbide irekiainfo:eu-repo/semantics/openAccess