Nitrate alleviates ammonium toxicity in Brassica napus by coordinating rhizosphere and cell pH and ammonium assimilation

SUMMARY In natural and agricultural situations, ammonium () is a preferred nitrogen (N) source for plants, but excessive amounts can be hazardous to them, known as toxicity. Nitrate () has long been recognized to reduce toxicity. However, little is known about Brassica napus , a major oil crop that is sensitive to high . Here, we found that can mitigate toxicity by balancing rhizosphere and intracellular pH and accelerating ammonium assimilation in B. napus . increased the uptake of and under high circumstances by triggering the expression of and transporters, while and H + efflux from the cytoplasm to the apoplast was enhanced by promoting the expression of efflux transporters and genes encoding plasma membrane H + ‐ATPase. In addition, increased pH in the cytosol, vacuole, and rhizosphere, and down‐regulated genes induced by acid stress. Root glutamine synthetase (GS) activity was elevated by under high conditions to enhance the assimilation of into amino acids, thereby reducing accumulation and translocation to shoot in rapeseed. In addition, root GS activity was highly dependent on the environmental pH. might induce metabolites involved in amino acid biosynthesis and malate metabolism in the tricarboxylic acid cycle, and inhibit phenylpropanoid metabolism to mitigate toxicity. Collectively, our results indicate that balances both rhizosphere and intracellular pH via effective transmembrane cycling, accelerates assimilation, and up‐regulates malate metabolism to mitigate toxicity in oilseed rape.