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Universität Wien (2015)

Drought response strategies mediated by plant-rhizobia interaction in Medicago truncatula.

Staudinger, Christiana

Titre : Drought response strategies mediated by plant-rhizobia interaction in Medicago truncatula.

Auteur : Staudinger, Christiana

Université de soutenance : Universität Wien

Grade : Doctor of Philosophy (PhD) 2015

Résumé
Drought stress hampers plant energy and biomass production ; however it is still unknown how internal C:N balance and rhizobial symbiosis impact on plant response to water limitation. Here, the effect of differential optimal nitrogen nutrition and root nodule symbiosis on drought stress and rehydration responses of Medicago truncatula was assessed. Two groups of plants were nodulated with Sinorhizobium medicae or S. meliloti ; the third group grew in a rhizobia-free medium and received mineral nitrogen fertilizer. In addition to growth analyses, physiological and molecular responses of the two systems were studied using ionomic, metabolomic and proteomic techniques. At the whole organism level two distinct strategies became apparent, when plants were exposed to comparable decreases in substrate water content. In non-nodulated plants older leaves underwent leaf senescence followed by leaf abscission. Nodulated plants maintained green leaves and showed a substantial delay in leaf abscission. This stay-green phenotype was empirically independent of the initial leaf N concentration and C/N ratio. However, differing nutritional balances played a role in the observed phenomenon, as revealed by an in-depth study of the S. medicae-nodulated and non-nodulated plant response to drought and rehydration. At the molecular level, the responses to drought and rehydration were similar in terms of soluble protein abundance and ion concentration changes. However, nodulation had an important effect on the plant metabolism under well-watered conditions. Nodulation was associated with higher concentrations of osmotically active compounds and a shift in daytime C allocation between starch and sugar pools. The differences in protein abundance provide indication that nodulation altered the plant’s hormonal balance, which could also play a role in the delay of drought-induced leaf senescence. This study shows that nodulation induces shifts within the plant’s metabolism that have the potential to favour leaf maintenance during water deprivation (nutritional priming). This stay-green phenotype is of interest for transient drought scenarios, where it may have a positive effect on plant growth and yield.

Mots clés : Drought stress / water deficit / stress tolerance / root nodule symbiosis / legume / metabolomics / proteomics / priming

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