FOR 948: Nitrogen Uptake, Metabolism and Remobilisation in Leaves during Plant Senescence

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Establishment of environmentally sound agriculture raises demands for a reduction of nitrogen (N) budget surpluses in crop production through a more efficient use of soil and fertilizer nitrogen. This requires the breeding and cultivation of genotypes with more efficient use of N, allowing a reduction in N supply without yield penalty. N efficiency of crops mainly depends on (1) maintenance of the N uptake capacity in the roots during reproductive growth and (2) efficient retranslocation of N from vegetative to reproductive plants organs during the seed-filling period resulting in leaf senescence. 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 mobilisation of N for reproductive growth and the maintenance of photosynthetic capacity is necessary. The overall hypothesis of the Research Unit is that an in-depth understanding of the physiological and molecular processes controlling leaf senescence in relation to N mobilisation and allocation to reproductive growth will allow developing traits for the breeding of N-efficient crop genotypes. In order to meet this challenge, the Research Unit is composed of plant scientists with agricultural and/or molecular biological background and a seed breeding company integrating studies at the molecular, biochemical, physiological, cytological and whole-plant level. As crops, oilseed rape and barley have been selected. In addition, Arabidopsis will be used for the identification of key genes regulating senescence and for their functional characterisation by reverse genetics. The main objectives of the experimental complementary approaches of the participating research groups are: (1) to characterise and compare the physiological processes and molecular signals governing developmentally regulated senescence versus N deficiency-induced senescence; (2) to determine time-dependent changes of senescence-associated parameters deciphering the potential bottlenecks in N uptake and retranslocation efficiencies; (3) to investigate whether and under which conditions N remobilisation during senescence is sink- or source-limited in relation to N uptake capacities of roots under progressing senescence; (4) to determine the potential for increasing N efficiency in crops by manipulating the expression of genes encoding transcription factors, signalling components, enzymes and transporters.