Integrated transcriptome and metabolome analysis reveals the physiological and molecular responses of allotetraploid rapeseed to ammonium toxicity

Ammonium (NH 4 + ) and nitrate (NO 3 − ) are the main nitrogen (N) sources accessible to plants. However, exclusive NH 4 + may causes toxicity to crops. Transcriptomics in conjunction with metabolomics analysis in allotetraploid rapeseed under NH 4 + stress showed that NH 4 + taken up by roots was mainly transferred to leaves for assimilation. The concentrations of most amino acids, glucose, and glucose-6-phosphate increased whilst malate, succinate, and α-ketoglutarate concentrations decreased in NH 4 + -treated leaves. Moreover, NH 4 + toxicity down-regulated genes related to photosynthesis and impaired the electron transport chain in chloroplasts. The expression of genes related to H 2 O 2 decomposition, as well as the concentrations of monodehydro-ascorbic acid and ascorbic acid, reduced after exposure to NH 4 + -N, accompanied by higher O 2 - and H 2 O 2 accumulation. Taken together, our results indicated that the excessive accumulation of NH 4 + in plants caused an imbalance of carbon and N metabolism, impaired photosystems and generated reactive oxygen species, which resulted in toxicity to rapeseed.