为了解决这个问题，研究了两个具有不同NO3吸收能力的根茎假单胞菌的根区。到根尖的0至40 mm区域（根部区域I）显示出净流入，而40至80 mm的区域（根部区域II）显示出净流出。II区的NO3-和铵（NH4+）浓度以及**还原酶（NR）活性低于I区。
Different root zones have distinct capacities for nitrate (NO3-) uptake in Populus species, but the underlying physiological and microRNA (miRNA) regulatory mechanisms remain largely unknown.
To address this question, two root zones of P. × canescens with contrasting capacities forNO3- uptake were investigated. The region of 0 to 40 mm (root zone I) to the root apex displayed net influxes, whereas the region of 40 to 80 mm (root zone II) exhibited net effluxes. Concentrations of NO3- and ammonium (NH4+) as well as nitrate reductase (NR) activity were lower in zone II than in zone I.
Forty one upregulated and twenty three downregulated miRNAs, and 576 targets of these miRNAs were identified in zone II in comparison with zone I. Particularly, growth-regulating factor 4 (GRF4), a target of upregulated ptc-miR396g-5p and ptc-miR396f_L + 1R-1, was downregulated in zone II in comparison with zone I, probably contributing to lower NO3-uptake rates and assimilation in zone II.
Furthermore, several miRNAs and their targets, members of C2H2 zinc finger family and APETALA2/ethylene-responsive element binding protein family, were found in root zones, which probably play important roles in regulating NO3- uptake. These results indicate that differentially expressed miRNA-target pairs play key roles in regulation of distinct NO3-uptake rates and assimilation in different root zones of poplars.