Responses of different nitrogen concentrations to carbon and nitrogen metabolism in tomato leaves

A hydroponic experiment was used to study the effects of different nitrogen supply levels [1) control: 0.3835 mmol/L (labelled 1/20N for CK); 2) 1/5N (1.534 mmol/L); 3) 1N (7.67 mmol/L); 4) 2N (15.34 mmol/L); 5) 3N (23.01 mmol/L)] on tomato ( Solanum lycopersicum L.) leaf carbohydrate and nitrogen metabolism. The results showed that after 9 d of treatment, the starch and sucrose contents in the leaves of the plants showed a trend of increasing and then decreasing with increasing nitrogen concentration, with the peak occurring in the medium nitrogen (1N) treatment; however, increased nitrogen application reduced glucose and fructose accumulation. The enzymes related to nitrogen metabolism (GDH) tended to increase and then decrease with increasing nitrogen concentration, with the highest values occurring in the medium nitrogen (1N) treatment group, while the enzyme activity of NADH-GOGAT showed the opposite trend, with the lowest values occurring in the 2N treatment group. A total of 6383 differentially expressed genes (DEGs) were identified in the leaf transcriptome analysis, which are involved in the 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.