ABA-mediated stress response with focus on salt-stress and trunk development

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Nitrate reductase [NR] is one of the best studied enzymes in herbaceous plants. However, little is known about nitrate assimilation in woody plants. Poplar as the model plant for trees with all of the known benefits will allow us to investigate this pathway in more detail. We will investigate the complex regulation of nitrate assimilation in woody plants by making use of our already existing knowledge of organ-specific expression of NR in tobacco. We will analyze the cross-talk between roots and shoot, the allocation of nitrate and reduced N-compounds between these organs, the threshold of N-assimilation exclusively in the roots and the storage capacity of N-compounds. Our work will be focused on different levels by (i) analyzing the already existing stably transformed poplar-lines containing different gene constructs including genes of NR and of the molybdenum cofactor biosynthetic pathway, (ii) producing a new set of transformed poplar plants be establishing the RNAi technique, and (iii) analyzing the promoter of NR. In tight collaboration with other groups of the Forschergruppe, these studies will give insights for poplar in the following areas: N-assimilation and allocation, importance of the different tissues for nitrate reduction, correlation between NR and the subsequent enzymes of the N-assimilation pathway, interaction with other organisms (mycorrhiza), importance of phytohormones for nitrate-uptake, importance of temperature and oxygen shortage for root N-assimilation (seasonal effects), influence of N-assimilation by salt stress.