Genotypic variation in nitrogen utilization efficiency in oilseed rape is related to the coordination of leaf senescence and root N uptake during reproductive stage.

Aims: Due to their low nitrogen utilization efficiency (NUtE) oilseed rape (OSR) crops require large quantities of nitrogen (N) fertilizer to achieve acceptable economic yields. Methods: To dissect the underlying mechanisms of oilseed NUtE, we investigated the relationships between NUtE, N uptake, N remobilization and leaf senescence by growing three N-efficient (genotypes with high NUtE at deficient N supplies) and three N-inefficient (ones with low NUtE at deficient N supplies) genotypes in pot experiments. Results: These genotypes showed similar plant N uptake before flowering and similar post-anthesis N remobilization from leaf and stem, but after flowering N-efficient genotypes exhibited higher root N uptake than N-inefficient genotypes. Besides, the pod biomass and leaf N concentration of N-efficient genotypes were higher than those of N-inefficient genotypes at 50 days after flowering, and we observed delayed leaf senescence in N-efficient genotypes. Correspondingly, gene transcripts involved in photosynthesis and carbon metabolism were abundant in green mature leaves of N-efficient genotype, while the expression of genes involved in ubiquitin mediated proteolysis pathway were more abundant in N-inefficient mature leaves. Conclusions: The stay-green phenotype of the N-efficient OSR after flowering provides sufficient photosynthate for root N uptake activity and pod development, and in turn, the prolonged post-anthesis N uptake provides more N to pods, leading to less leaf N remobilization requirement. This work has identified traits important for breeding OSR cultivars with improved NUtE. [ABSTRACT FROM AUTHOR]