Regulation of nitrogen storage and mobilization in the annual life cycle of poplar

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Nitrogen nutrition is a major growth limiting factor for trees and, therefore, nitrogen uptake and assimilation are highly regulated. Recently it was shown that beside reduced nitrogen compounds, e.g. glutamine, phytohormones such as cytokinins regulate nitrate uptake. The central aim of this project is to test the hypothesis that two antagonistic regulatory pathways are involved in the adaptation of N uptake by the roots to the N-demand of trees: (1) The enrichment of particular amino compounds serves as signal for the repression of nitrogen uptake and (2) the enrichment of cytokinins increases the expression of genes involved in nitrogen uptake and assimilation. A combination of molecular and physiological methods with computer modelling will be used to assess the regulation of N-metabolism by reduced N-compounds and cytokinins in poplar and their cycling within the plant.