Salicylic Acid Is Involved in the Growth Inhibition Caused by Excessive Ammonium in Oilseed Rape ( L.).

Rapeseed ( L.) is extremely sensitive to excessive NH toxicity. There remains incomplete knowledge of the causal factors behind the growth suppression in NH-nourished plants, with limited studies conducted specifically on field crop plants. In this study, we found that NH toxicity significantly increased salicylic acid (SA) accumulation by accelerating the conversion of SA precursors. Moreover, exogenous SA application significantly aggravated NH toxicity symptoms in the rapeseed shoots. Genome-wide differential transcriptomic analysis showed that NH toxicity increased the expression of genes involved in the biosynthesis, transport, signaling transduction, and conversion of SA. SA treatment significantly increased shoot NH concentrations by reducing the activities of glutamine synthase and glutamate synthase in NH-treated rapeseed plants. The application of an SA biosynthesis inhibitor, ABT, alleviated NH toxicity symptoms. Furthermore, SA induced putrescine (Put) accumulation, resulting in an elevated ratio of Put to [spermidine (Spd) + spermine (Spm)] in the NH-treated plants, while the opposite was true for ABT. The application of exogenous Put and its biosynthesis inhibitor DFMA induced opposite effects on NH toxicity in rapeseed shoots. These results indicated that the increased endogenous SA contributed noticeably to the toxicity caused by the sole NH-N supply in rapeseed shoots. This study provided fresh perspectives on the mechanism underlying excessive NH-induced toxicity and the corresponding alleviating strategies in plants.