AUTHOR=Tian Jing , Pang Yue , Zhao Zhong 

TITLE=Drought, Salinity, and Low Nitrogen Differentially Affect the Growth and Nitrogen Metabolism of Sophora japonica (L.) in a Semi-Hydroponic Phenotyping Platform

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.715456

DOI=10.3389/fpls.2021.715456

ISSN=1664-462X

ABSTRACT=<p>Abiotic stresses, such as salinity, drought, and nutrient deficiency adversely affect nitrogen (N) uptake and assimilation in plants. However, the regulation of N metabolism and N pathway genes in <italic>Sophora japonica</italic> under abiotic stresses is unclear. <italic>Sophora japonica</italic> seedlings were subjected to drought (5% polyethylene glycol 6,000), salinity (75mM NaCl), or low N (0.01mM NH<sub>4</sub>NO<sub>3</sub>) for 3weeks in a semi-hydroponic phenotyping platform. Salinity and low N negatively affected plant growth, while drought promoted root growth and inhibited aboveground growth. The NH<sub>4</sub><sup>+</sup>/NO<sub>3</sub><sup>−</sup> ratio increased under all three treatments with the exception of a reduction in leaves under salinity. Drought significantly increased leaf NO<sub>2</sub><sup>−</sup> concentrations. Nitrate reductase (NR) activity was unaltered or increased under stresses with the exception of a reduction in leaves under salinity. Drought enhanced ammonium assimilation with increased glutamate synthase (GOGAT) activity, although glutamine synthetase (GS) activity remained unchanged, whereas salinity and low N inhibited ammonium assimilation with decreased GS activity under salt stress and decreased GOGAT activity under low N treatment. Glutamate dehydrogenase (GDH) activity also changed dramatically under different stresses. Additionally, expression changes of genes involved in N reduction and assimilation were generally consistent with related enzyme activities. In roots, ammonium transporters, especially <italic>SjAMT1.1</italic> and <italic>SjAMT2.1a</italic>, showed higher transcription under all three stresses; however, most nitrate transporters <italic>(NRTs)</italic> were upregulated under salinity but unchanged under drought. <italic>SjNRT2.4</italic>, <italic>SjNRT2.5</italic>, and <italic>SjNRT3.1</italic> were highly induced by low N. These results indicate that N uptake and metabolism processes respond differently to drought, salinity, and low N conditions in <italic>S. japonica</italic> seedlings, possibly playing key roles in plant resistance to environmental stress.</p>