Proteomic reconfigurations underlying physiological alterations in poplar roots in acclimation to changing nitrogen availability

Although the roots of woody plants are essential for nitrogen (N) uptake and assimilation, proteomic regulation underlying these processes is unclear in acclimation to changing N availability. Here, we carried out physiological and proteomic assays in Populus × canescens sapling roots treated with one of low, normal and high levels of NH4NO3. N deficiency induced lower concentrations of NH4+, total N, amino acids, inhibited enzymatic activities of nitrate reductase and glutamate synthase, decreased levels of abscisic acid and salicylic acid in poplar roots, and high N had the opposite effects. There were 552 and 247 significantly differentially abundant proteins (DAPs) in low and high vs normal N-supplied poplar roots, respectively. Notably, the abundances of a few poplar proteins, including nitrite reductase 1, glutamate synthase 1, and glutamate dehydrogenase 1, corresponded well to N-induced physiological changes in poplar roots. Functional characterization of N-responsive poplar ammonium transporter 2;1 and glutamate dehydrogenase 2 suggests both play pivotal roles in N uptake and assimilation in response to altering N levels. These results suggest that the growth, N uptake and assimilation, and phytohormonal levels are inhibited by N deficiency, but stimulated by high N, and the proteomic reconfigurations occur underlying these physiological alterations in poplars in acclimation to changing N availability.