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.

Automated summary

This study investigated the mechanisms of nitrogen utilization efficiency in oilseed rape, finding that N-efficient genotypes exhibited higher root N uptake and delayed leaf senescence after flowering, leading to higher pod biomass and leaf N concentration. Gene expression analysis revealed differences in photosynthesis and carbon metabolism between N-efficient and N-inefficient genotypes, providing insight into traits important for breeding cultivars with improved nitrogen utilization efficiency.