Abstract: 【Objective】Nitrogen (N) uptake efficiency is one of the important factor affecting crop N efficiency, investigating characteristics of efficient N uptake and transport is purpose to provide theoretical basis for improving N efficiency and yield of rapeseed varieties.【Method】To explore the mechanisms underlying high N uptake and transport in rapeseed, two rapeseed germplasms with contrasting N efficiency (N efficient germplasm ‘498’ and N inefficient germplasm ‘428’) were used in this study under normal N (9.5 mmol·L^-1) and N starvation (0.475 mmol·L^-1) at three different growth stages (Phenological growth stages 12, 14 and 16) in hydroponic culture. At the same time, the ¹⁵N isotope tracer technique was applied to study the uptake and transport capacity of NO₃^? and NH₄⁺. Additionally, the expression level of genes (BnNPFs, BnNRT2s and BnAMTs）related to N uptake and transport in rapeseed germplasms with contrasting N efficiency were further analyzed by real-time quantitative PCR (qRT-PCR).【Result】Rapeseed germplasm ‘498’ showed superior advantages in plant growth and root development under different N concentrations, and the root morphological indexes (main root length, total root length, root surface area, root volume and lateral root number), biomass, N accumulation and N uptake efficiency were all significantly greater than those of germplasm ‘428’. ¹⁵N isotope tracer test also showed that ‘498’ showed greater advantage in the uptake and accumulation of NO₃^- and NH₄⁺, especially for NH₄⁺, as indicated by the significant differences in the accumulation of ¹⁵NH₄⁺ between two germplasms. qRT-PCR analysis further found that under normal N conditions, the relative expressions of BnNPF6.3a, BnNRT2.1e, BnNPF7.2a, BnNPF7.2c, BnNPF6.2c, BnAMT1;2a, BnAMT1;3c, BnAMT1;4a, BnAMT2;1a and BnAMT2;1b (involved in the uptake and transport of NO₃^- and NH₄⁺) was Significantly higher in ‘498’ than that in ‘428’. While under N starvation stress, the relative expressions of BnNRT2.4a、BnNRT2.5a and BnNRT2.5b (involved in NO₃^- uptake and transport) was significantly lower in the root of ‘498’ than that of ‘428’, but the expression level of BnNPF7.3a and BnNPF6.2c (referred to NO₃^- transport and redistribution) was significantly higher in ‘498’ than that in ‘428’, as well as the expression level of BnAMT1;1a、BnAMT1;2a、BnAMT1;3c、BnAMT1;4a、BnAMT2;1a and BnAMT2;1b (involved in NH₄⁺ uptake and transport).【Conclusion】Compared with N-inefficient germplasm ‘428’, N-efficient germplasm ‘498’ were superior in root length, root surface (volume) and lateral root number, additionally with greater ability in N (especially NH₄⁺) uptake and accumulation. Under normal N conditions, the expression of genes involved in NO₃^- and NH₄⁺ absorption and transport were relatively higher in ‘498’, while the relative expression of genes involved in the NO₃^- transport and redistribution as well as NH₄⁺ absorption and transport were significantly higher in ‘498’ than that in ‘428’ under N deficiency stress, illustrating the relative higher N uptake efficiency of ‘498’ possibly link to the higher expressions of several BnNPFs sand BnAMTs.

Key words: rapeseed, high nitrogen efficiency, root morphology, uptake and transport, nitrogen transporter genes