Ammonium-mediated reduction in salicylic acid content and recovery of plant growth in Arabidopsis mutants is modulated by NDR1 and NPR1.

The mutants exhibit high SA accumulation and consequently severe dwarfism. Although mutants exhibit growth recovery upon exogenous ammonium supply, the underlying mechanism remains unknown. Here, we investigated the effect of ammonium on SA level and plant growth in SA-accumulating mutants. The growth of and mutants was recovered to wild-type (WT) levels upon exogenous ammonium supply, but that of () and () double mutants was unaffected. The SA level was decreased by exogenous ammonium application in , and mutants. The level of nitrate reductase (NR) was almost the same in all genotypes (WT, , and ), regardless of the ammonium treatment, suggesting that exogenous ammonium supply to and double mutants does not have any effect on their growth and NR levels, but decreases the SA level. Taken together, these results indicate that ammonium acts as a signaling molecule to regulate the SA amount, and NDR1 and NPR1 play a positive role in the ammonium-mediated growth recovery of mutants.