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PLANTS INTERACTING WITH OTHER ORGANISMS

Nitrogen Fixation Control under Drought Stress. Localized or Systemic?^1,[OA]

Departamento de Ciencias del Medio Natural, Universidad Pública de Navarra, Campus Arrosadía, 31006 Pamplona, Spain (D.M., R.L., A.Z., C.A.-I., E.M.G.); and Interactions Plantes-Microorganismes et Santé Végétale, UMR INRA 1064/Université de Nice Sophia-Antipolis/CNRS 6192, F–06903 Sophia-Antipolis, France (P.F., A.P.)

Legume-Rhizobium nitrogen fixation is dramatically affected under drought and other environmental constraints. However, it has yet to be established as to whether such regulation of nitrogen fixation is only exerted at the whole-plant level (e.g. by a systemic nitrogen feedback mechanism) or can also occur at a local nodule level. To address this question, nodulated pea (Pisum sativum) plants were grown in a split-root system, which allowed for half of the root system to be irrigated at field capacity, while the other half was water deprived, thus provoking changes in the nodule water potential. Nitrogen fixation only declined in the water-deprived, half-root system and this result was correlated with modifications in the activities of key nodule's enzymes such as sucrose synthase and isocitrate dehydrogenase and in nodular malate content. Furthermore, the decline in nodule water potential resulted in a cell redox imbalance. The results also indicate that systemic nitrogen feedback signaling was not operating in these water-stressed plants, since nitrogen fixation activity was maintained at control values in the watered half of the split-root plants. Thus, the use of a partially droughted split-root system provides evidence that nitrogen fixation activity under drought stress is mainly controlled at the local level rather than by a systemic nitrogen signal.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Esther M. González (esther.gonzalez{at}unavarra.es).

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.097139

^* Corresponding author; e-mail esther.gonzalez{at}unavarra.es; fax 34–948168930.

Received February 1, 2007; accepted February 20, 2007; published March 2, 2007.

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