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Establishment of environmentally-sound agriculture raises demands for a reduction of N budget surpluses in crop production through a more efficient use of soil and fertilizer nitrogen (N). This requires the breeding and cultivation of genotypes with more efficient use of N, allowing a reduction in N supply without yield penalty. Nitrogen efficiency of crops mainly depends on i) maintenance of the N uptake capacity in the roots during reproductive growth and ii) efficient retranslocation of N from vegetative to reproductive plant organs during the seed-filling.

Since leaf senescence leads to decreased allocation of photosynthates to roots (reducing N uptake) and seeds (reducing grain yields) a fine tuning of leaf senescence regarding the mobilization of N for reproductive growth and the maintenance of photosynthetic capacity is necessary. The overall hypothesis of this research project is that an in-depth understanding of the physiological and molecular processes controlling leaf senescence in relation to N mobilization and allocation to reproductive growth will allow developing traits for the breeding of N-efficient crop genotypes.

The main objectives of the experimental complementary approaches of the participating research groups are:
- to characterize and compare the physiological processes and molecular signals governing developmentally regulated senescence versus N deficiency-induced senescence;
- to determine time-dependent changes of senescence-associated parameters deciphering the potential bottlenecks in N uptake and retranslocation efficiencies;
- to investigate whether and under which conditions N remobilization during senescence is sink- or source-limited in relation to N uptake capacities of roots under progressing senescence;
- to determine the potential for increasing N efficiency in crops by manipulating the expression of genes encoding transcription factors, signalling components, enzymes or transporters.