{Reference Type}: Journal Article
{Title}: Nitrate alleviates ammonium toxicity in Brassica napus by coordinating rhizosphere and cell pH and ammonium assimilation.
{Author}: Li S;Yan L;Zhang W;Yi C;Haider S;Wang C;Liu Y;Shi L;Xu F;Ding G;
{Journal}: Plant J
{Volume}: 117
{Issue}: 3
{Year}: 2024 Feb 13
{Factor}: 7.091
{DOI}: 10.1111/tpj.16529
{Abstract}: In natural and agricultural situations, ammonium (  NH 4 +   ) is a preferred nitrogen (N) source for plants, but excessive amounts can be hazardous to them, known as  NH 4 +   toxicity. Nitrate (  NO 3 -   ) has long been recognized to reduce  NH 4 +   toxicity. However, little is known about Brassica napus, a major oil crop that is sensitive to high  NH 4 +   . Here, we found that  NO 3 -   can mitigate  NH 4 +   toxicity by balancing rhizosphere and intracellular pH and accelerating ammonium assimilation in B. napus.  NO 3 -   increased the uptake of  NO 3 -   and  NH 4 +   under high  NH 4 +   circumstances by triggering the expression of  NO 3 -   and  NH 4 +   transporters, while  NO 3 -   and H+ efflux from the cytoplasm to the apoplast was enhanced by promoting the expression of  NO 3 -   efflux transporters and genes encoding plasma membrane H+ -ATPase. In addition,  NO 3 -   increased pH in the cytosol, vacuole, and rhizosphere, and down-regulated genes induced by acid stress. Root glutamine synthetase (GS) activity was elevated by  NO 3 -   under high  NH 4 +   conditions to enhance the assimilation of  NH 4 +   into amino acids, thereby reducing  NH 4 +   accumulation and translocation to shoot in rapeseed. In addition, root GS activity was highly dependent on the environmental pH.  NO 3 -   might induce metabolites involved in amino acid biosynthesis and malate metabolism in the tricarboxylic acid cycle, and inhibit phenylpropanoid metabolism to mitigate  NH 4 +   toxicity. Collectively, our results indicate that  NO 3 -   balances both rhizosphere and intracellular pH via effective  NO 3 -   transmembrane cycling, accelerates  NH 4 +   assimilation, and up-regulates malate metabolism to mitigate  NH 4 +   toxicity in oilseed rape.