Nitrogen Absorption Pattern Detection and Expression Analysis of Nitrate Transporters in Flowering Chinese Cabbage

Nitrate transporters (NRTs) play an important role in nitrate absorption and internal distribution in plant roots and other parts. Experiments were carried out to explore the sequences and expression characteristics of NRT genes, and their correlation with the N uptake in flowering Chinese cabbage. We have isolated three important BcNRTs (BcNRT1.1, BcNRT1.2, and BcNRT2.1) from flowering Chinese cabbage. Spatio-temporal expression analysis found that BcNRT1.1 and BcNRT2.1 were mainly expressed in roots, while BcNRT1.2 was more expressed in roots than in leaves during vegetative growth and was mainly expressed in leaves during reproductive growth. The NO3&minus: uptake rate of the entire growth period was significantly correlated with BcNRT1.1 and BcNRT1.2 expression in roots. In addition, the total N content was increased with the increase in NO3&minus: concentration in flowering Chinese cabbage. The NH4+ uptake was slightly induced by NH4+, but the total N content had no significant difference under the NH4+ concentration of 1&ndash:8 mmol/L. We also found that lower concentrations of NH4+ promoted the expression of BcNRT1.1 and BcNRT1.2 while inhibiting the expression of BcNRT2.1 in the roots of flowering Chinese cabbage. The amount of total N uptake in the treatment with 25/75 of NH4+/NO3&minus: was significantly higher than that of the other two treatments (0/100 and 50/50). In the mixture of NH4+ and NO3&minus:, total N uptake was significantly correlated with the BcNRT1.2 expression. We concluded that mixed nutrition with an NH4+/NO3&minus: of 25/75 could significantly increase total nitrogen uptake in flowering Chinese cabbage, in which two members of the NRT1 subfamily (BcNRT1.1 and BcNRT1.2) might play a major regulatory role in it. This study is a beneficial attempt to dig deeper into the NRT genes resources and lays the foundation for the ultimate use of genetic improvement methods to increase the NUE with less nitrogen fertilizer in flowering Chinese cabbage.