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

建立无害环境的农业提出了通过更有效地利用土壤和肥料氮来减少作物生产中氮预算盈余的要求。这就要求育种和培育能更有效利用氮的基因型，在不影响产量的情况下减少氮供应。作物的氮素效率主要取决于(1)生殖生长期间根系对氮素吸收能力的维持；(2)种子灌浆期间氮素从营养植物器官向生殖植物器官的有效再转运，从而导致叶片衰老。由于叶片衰老导致分配给根系的光合产物减少（减少氮素吸收）和种子减少（减少籽粒产量），因此需要对叶片衰老进行微调，以调动用于生殖生长的氮素和维持光合能力。该研究单位的总体假设是，深入了解控制叶片衰老的生理和分子过程与N的动员和分配到生殖生长有关，将有助于开发培育氮高效作物基因型的性状。为了应对这一挑战，研究部由具有农业和/或分子生物学背景的植物科学家和一家种子育种公司组成，该公司在分子、生化、生理、细胞学和整个植物水平上进行综合研究。农作物选择了油菜和大麦。此外，拟南芥将被用于鉴定调节衰老的关键基因，并通过反向遗传学对其功能特征进行表征。参与研究小组的实验互补方法的主要目标是：(1)表征和比较发育调节的衰老与氮缺乏诱导的衰老的生理过程和分子信号；(2)确定衰老相关参数随时间的变化，揭示氮吸收和重转运效率的潜在瓶颈；(3)研究衰老过程中氮的再动员是否以及在何种条件下受到根系吸收氮能力的汇或源限制；(4)通过调控编码转录因子、信号组分、酶和转运体的基因表达，确定提高作物氮效率的潜力。

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.