In order to identify the genetic variations in root system architecture traits and their probable association with high- and low-affinity nitrate transport system, we performed several experiments on a genetically diverse set of wheat genotypes grown under two external nitrogen levels (optimum and limited nitrate conditions) at two growth points of the seedling stage. Further, we also examined the nitrate uptake and its transport under different combinations of nitrate availability in the external media using 15N-labelled N-source (15NO3-), and gene expression pattern of different high- and low-affinity nitrate transporters. We observed that nitrate starvation invariably increases the total root size in all genotypes. However, the variation of component traits of total root size under nitrate starvation is genotype-specific at both stages. Further, we also observed genotypic variation in both nitrate uptake and translocation depending on the growth stage, external nitrate concentration and growing conditions. The expression of the TaNRT2.1 gene was invariably up-regulated under low external nitrate concentration; however, it gets reduced after a longer period (21 days) of starvation than the early stage (14 days). Among the four NRT1.1 orthologs, TaNPF6.3 and TaNPF6.4 consistently showed higher expression than TaNPF6.1 and TaNPF6.2 at higher nitrate concentration at both the growth stages. TaNPF6.3 and TaNPF6.4 apparently showed a feature of typical low-affinity nitrate transporter gene at higher external nitrate concentration at 14 and 21 days growth stages, respectively. The present study reveals the complex root system of wheat that has genotype-specific N-foraging along with highly coordinated high- and low-affinity nitrate transport systems for nitrate uptake and transport.

中文翻译：

---

在不同外部氮浓度下，不同基因型小麦根系结构特征变化和硝酸盐流入响应。

为了确定根系结构特征的遗传变异及其与高亲和力和低亲和力硝酸盐转运系统的可能关联，我们对在两个外部氮水平（最佳和有限硝酸盐）下生长的一组遗传多样的小麦基因型进行了几次实验条件）在苗期的两个生长点。此外，我们还使用15N标记的N源（15NO3-）在外部培养基中硝酸盐可用性的不同组合下研究了硝酸盐的吸收及其转运，以及不同高亲和力和低亲和力硝酸盐转运蛋白的基因表达模式。我们观察到硝酸盐饥饿总是增加所有基因型的总根大小。然而，在硝酸盐饥饿下，总根大小的组分性状的变化在两个阶段都是基因型特异性的。进一步，我们还观察到硝酸盐吸收和转运的基因型差异，取决于生长阶段，外部硝酸盐浓度和生长条件。在较低的外部硝酸盐浓度下，TaNRT2.1基因的表达总是上调。但是，饥饿时间比早期（14天）更长（21天），饥饿感会降低。在四个NRT1.1直系同源物中，在两个生长阶段，在较高的硝酸盐浓度下，TaNPF6.3和TaNPF6.4始终显示出高于TaNPF6.1和TaNPF6.2的表达。TaNPF6.3和TaNPF6.4明显表现出典型的低亲和力硝酸盐转运蛋白基因的特征，分别在较高的外部硝酸盐浓度下分别处于14和21天的生长阶段。