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Effects of nutrients on N-fixation of Lotus spp. and Rhizobium strains:

Supervisor: Stefanie Wienkoop

PhD student: Sebastian Schneider

Group: Plant-Systems Interactions, Division of Molecular Systems Biology, Department of Ecogenomics and Systems Biology




Metabolic plant-bacteroid exchange during nodule senescence


Rhizobium symbiosis facilitates plant N-nutrition through N2-fixation, the most common interaction with legumes in nature.

Stress induced senescence is negatively effecting symbiotic N2-fixation. Increased nitrogen supply also induces nodule senescence. Along the decline of N2- fixation, metabolic exchange of amino acids (AA), soluble sugar and sulfate (S) between the symbionts is impaired causing accumulation of the substrates within the plant. There are several questions to be addressed. For instance:

• What role plays S in the symbiotic interaction?

• Is it possible to monitor the metabolic adjustment  when the plant is changing from  symbiotic N-fixation to N-nutritional assimilation

 15N gas and nutritional labelling as well as 36S nutrition labelling experiments along with several front-end mass spectrometry  analyses techniques (LC-MS/MS, GC-MS and NanoSIMS-imaging) will be conducted to gain deeper insides into the metabolic exchange and the incorporation of N and S into plant and bacteroid AA and proteins during induced nodule senescence.

 In the case of a blockage of the nitrogen transport to the plant 36S pulse labelling will be necessary to further asses N-fixation independent N-cycling of the plant. The differential labelling strategies will enable to distinguish between diversely regulated N-cycles.

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