Abstract
Nickel (Ni) is an essential trace element for plant growth and a component of the plant body that has many different functions in plants. Although it has been confirmed that nickel ions (Ni(2+)) havea certain regulatory effect on nitrogen (N) metabolism, there are not enough data to prove whether exogenous Ni(2+) can increase the carbon (C) and N metabolism in the roots of tomato seedlingsunder low-nitrogen (LN) conditions. Therefore, through the present experiment, we revealed the key mechanism of Ni(2+)-mediated tomato root tolerance to LN levels. Tomato plants were cultured at two different N levels (7.66 and 0.383 mmol L(-1)) and two different Ni(2+) levels (0 and 0.1 mg L(-1) NiSO(4) 6H(2)O) under hydroponic conditions. After nine days, we collected roots for physiological, biochemical, and transcriptome sequencing analyses and found that the activities of N assimilation-related enzymes decreased at LN levels. In contrast, Ni(2+) significantly increased the activities of N assimilation-related enzymes and increased the contents of nitrate (NO(3)(-)), ammonium (NH(4)(+)), and total amino acids. Through root transcriptomic analysis, 3738 differentially expressed genes (DEGs) were identified. DEGs related to C and N metabolism were downregulated after LN application. However, after Ni(2+) treatment, PK, PDHB, GAPDH, NR, NiR, GS, GOGAT, and other DEGs related to C and N metabolism were significantly upregulated. In conclusion, our results suggest that Ni(2+) can regulate the C and N metabolism pathways in tomato roots to alleviate the impact of LN levels.