Ammonium Transporter () Mediates the Interaction of Ammonium and Nitrate in .

The provision of ammonium (NH ) and nitrate (NO ) mixture increases the total nitrogen (N) than the supply of sole NH or NO with the same concentration of total N; thus, the mixture contributes to better growth in . However, the underlying mechanisms remain unknown. In this study, we analyzed NH and NO fluxes using a scanning ion-selective electrode technique to detect under different N forms and levels in roots. We observed that the total N influxes with NH and NO mixture were 1.25- and 3.53-fold higher than those with either sole NH or NO . Furthermore, NH and NO might interact with each other under coexistence. NO had a positive effect on net NH influx, whereas NH had a negative influence on net NO influx. The ammonium transporter (AMT) played a key role in NH absorption and transport. Based on expression analysis, differed from other in being upregulated by NH or NO . According to sequence analysis and functional complementation in yeast mutant 31019b, AMT1.2 from may be a functional AMT. According to the expression pattern of , β-glucuronidase activity, and the cellular location of its promoter, BcAMT1.2 may be responsible for NH transport. Following the overexpression of in , -overexpressing lines grew better than wildtype lines at low NH concentration. In the mixture of NH and NO , NH influxes and NO effluxes were induced in -overexpressing lines. Furthermore, transcripts of N assimilation genes (, , and ) were significantly upregulated, in particular, and were increased by 2.85-8.88 times in roots, and and were increased by 2.67-4.61 times in leaves. Collectively, these results indicated that may mediate in NH fluxes under the coexistence of NH and NO in .