【Objective】Nitrogen (N) uptake efficiency is one of the important factors affecting crop N efficiency, investigating characteristics of efficient N uptake and transport was the purpose to provide the theoretical basis for improving N efficiency and yield of rapeseed (Brassica napus L.) 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 low N (0.475 mmol·L-1) conditions 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 (RT-qPCR).【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. The RT-qPCR 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 low N 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 area (volume) and lateral root number, additionally with greater ability in N (especially NH4+) uptake and accumulation. Under normal N application 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 low N stress, illustrating the relative higher N uptake efficiency of ‘498’ possibly linked to the higher expressions of several BnNPFs sand BnAMTs.

为探究氮高效的机制,研究油菜苗期碳氮代谢规律,以两个氮效率差异显著的油菜种质(氮高效种质A294和氮低效种质A364)为材料,通过设置正常(CK,9.5 mmol/L)和低氮(LN,0.475 mmol/L)两个处理,比较不同氮效率油菜在根系形态、氮吸收转运同化、光合碳代谢生理指标以及碳氮代谢相关基因表达等方面的差异.结果表明,氮高效的A294在低氮胁迫下根系发达,植株生物量和氮累积量显著高于A364,前者根系吸收及向地上部转运氮的能力较强,而氮同化关键酶硝酸还原酶和谷氨酰胺合成酶活性在两个种质间无显著差异;同时,A294叶片SPAD值、光合色素含量、净光合速率及磷酸蔗糖合酶基因BnaSPS的表达均更高.进一步分析发现,低氮胁迫下A294根系中硝酸盐转运蛋白基因BnaNPF7.3的表达显著高于A364,而BnaNPF7.2b在A364根系的表达则显著高于A294;此外,A364可溶性糖含量的根叶比及根系中蔗糖合酶基因BnaSUS表达高于A294,说明低氮胁迫下氮高效油菜A294可以将更多的营养元素(氮)分配至地上部,使叶片保持较高的光合速率,为生物体构建提供保障;而氮低效油菜种质A364则倾向于将有限的营养元素(氮)分配在根系并维持其生长发育,同时其根系可溶性糖消耗占比高于A294,导致其根冠比高于A294.由此认为,油菜在响应外界氮缺乏胁迫时,氮素与能量物质(可溶性糖)的分配与消耗差异会影响叶片碳代谢(光合作用、蔗糖合成)速率,最终导致油菜苗期氮效率的差异.