Net NH4 + and NO3 − fluxes, and expression of NH4 + and NO3 − transporter genes in roots of Populus simonii after acclimation to moderate salinity

Abstract

Key message Net NH 4 1 flux was higher in fine roots of P. simonii after NaCl treatment compared to the NO 3 2 flux which was consistent with the expression levels of AMTs and NRTs. Abstract The characteristics of nitrogen uptake under salt stress would provide insights into the mechanisms of salt tolerance in plants. In the present study, net NH 4 ? and NO 3 -fluxes were measured using the non-invasive microtest technique, and transcript abundance of ammonium/ nitrate transporter genes (AMTs/NRTs) were determined by real time PCR in the fine roots of Populus simonii after treatment for 21 days with 75 mM NaCl. The NH 4 ? and NO 3 -fluxes showed heterogeneous spatial patterns along the root tip in nutrient solution. The maximum influx of NH 4? occurred near the root tip, while that of NO 3 -was 15 mm from the root tip. The net NO 3 -flux was inhibited by ca. 25 % with the provision of NH 4? . On average, the newly grown fine roots took up more NH 4 ? after the 75 mM NaCl treatment than did the control. Consistent with the NH 4 ? and NO 3 -influxes, most AMTs were upregulated in the salt-treated roots relative to the control, while most NRTs were down-regulated. Our study provides insights into nitrogen uptake and the AMT/NRT expression levels in the fine roots of P. simonii after acclimation to moderate salinity. This may be valuable for understanding nitrogen uptake mechanisms after adaptation to salinity.

Nitrate and Ammonium Contribute to the Distinct Nitrogen Metabolism of Populus simonii during Moderate Salt Stress

“…However, increases in N uptake and soluble protein were not observed in the NO 3 - fed plants. These results indicate enhanced NH 4 + uptake during salt treatment; similar results were also reported in the roots of Picea glauca [ 5 , 30 ]. These changes might reflect cation exchange because NH 4 + application could lower the uptake of cations in plant tissues compared to NO 3 - -treated plants [ 9 ].…”

“…NaCl stress leads to various deleterious effects at morphological, physiological, biochemical and molecular levels. Salinity affects nitrification and ammonification in the soil [ 4 ], thus, the deleterious effect of NaCl stress on plant growth might relate to changes of nitrogen (N) uptake and metabolism [ 5 ] since N is one of the key mineral nutrients for plant growth and development.…”

“…simonii in response to different N sources (NO 3 - or NH 4 + ) during moderate salt stress, we examined several morphological (root characteristics), physiological (e.g., photosynthesis, N metabolism enzyme activities, total N concentration and amino acid compounds) and molecular (transcript levels of representative genes involved in N metabolism) changes relevant for N metabolism in response to the N source under salt stress. Based on our previous study [ 5 ] and the ecological conditions of P . simonii , we proposed that NH 4 + -fed P .…”

Distinct effect of pH on N uptake and assimilation in two conifer species

“…is assimilated to glutamine and glutamate via GS and GOGAT, and the products of the GS/GOGAT pathway are required for the biosynthesis of other nitrogenous compounds. Each step of N metabolism can be influenced by species and environmental factors (soil type, water availability, salt and climate) (Cousins and Bloom 2003;Dong et al 2001;Luo et al 2013a, b;Zhang et al 2014). For instance, some maize varieties displayed a higher capacity to absorb and utilize N than the others (Machado and Fernandes 2001)).…”

“…Populus simonii took up more NH 4 ? after acclimation to moderate salinity (Zhang et al 2014). However, little information is available on responses of N metabolism in woody plants to pH changes.…”