Carbon and nitrogen metabolism in tomato (solanum lycopersicum L.) leaves response to nitrogen treatment

A hydroponic experiment was used to study the effects of different nitrogen supply levels [1) control: 0.3835 mmol/L (labelled 1/20 N for CK); 2) 1/5 N (1.534 mmol/L); 3) 1 N (7.67 mmol/L); 4) 2 N (15.34 mmol/L); 5) 3 N (23.01 mmol/L)] on tomato (Solanum lycopersicum L.) leaf carbohydrate and nitrogen metabolism. The results showed that after 9 days of treatment, the contents of starch and sucrose in tomato leaves increased first and then decreased with the increase of nitrogen concentration, and reached the highest value in 1 N treatment. With the increase of nitrogen concentration, the contents of glucose and fructose decreased. The enzymes related to nitrogen metabolism (Glutamate dehydrogenase) tended to increase and then decrease with increasing nitrogen concentration, with the highest values occurring in the medium nitrogen (1 N) treatment group, while the enzyme activity of NADH- Glutamate synthase showed the opposite trend, with the lowest values occurring in the 2 N treatment group. A total of 6383 differentially expressed genes (DEGs) were identified in the leaf transcriptome analysis, which are involved in the aerobic glycolysis tricarboxylic acid cycle, amino acid biosynthesis and nitrogen metabolism pathways, and related transcriptional regulatory pathways were constructed. Thus, this study reveals the mechanisms of tomato leaf carbon and nitrogen metabolism in response to nitrogen supply levels at the physiological, biochemical and transcriptional regulatory levels, providing valuable insights for further understanding nitrogen metabolism mechanisms and guiding nitrogen utilization in tomato.