Synergism between potassium and nitrate enhances the alleviation of ammonium toxicity in rice seedling root

Ammonium toxicity in plants is considered a global phenomenon, but the primary mechanisms remain poorly characterized. Here, we showed that although the addition of potassium (K+) or nitrate (NO3-) partially alleviated the inhibition of rice root growth caused by ammonium toxicity, the coexistence of K+ and NO3- clearly improved the alleviation via a synergistic mechanism. The synergism led to significantly improved alleviation effects on root biomass, length, surface area, number and meristem cell number. The aberrant auxin distribution in root tips, rhizosphere acidification level and abnormal cell morphology in the root cap and elongation zone caused by ammonium toxicity could be recovered by this synergism. RNA sequencing and the weighted gene correlation network analysis (WGCNA) revealed that the mechanism of this synergism involves cellulose synthesis, auxin and gibberellin metabolism regulation at the transcription level.