Physiological and transcriptomic responses of antioxidant system and nitrogen metabolism in tomato seedlings treated with nitrogen starvation and re-supply

Nitrogen (N) is one of the essential macronutrients that play important roles in plant growth and development. To better understand the response of antioxidant system and Nmetabolism under Nstarvation and re-supply condition, physiological and transcriptomic analyses were performed in tomato (Solanum lycopersicum L.). The malondialdehyde (MDA) and reactive oxygen species (ROS) contents increased significantly, while the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) activities, the ratio of ASA/DHA and GSH/GSSG, the NO3− contents, nitrate reductase (NR) activities decreased after Nstarvation treatment. Compared with the control, 1766 genes were up-regulated and 2244 genes were down-regulated after Nstarvation. These differentially expressed genes (DEGs) are mainly enriched in functional items such as cellular process, metabolic process and catalytic activity. The KEGG pathways revealed that the DEGs were mainly involved in phenpropane biosynthesis, amino sugar and nucleotide sugar metabolism, and Nmetabolism. The expression of SlSOD, SlCAT, SlAPX, SlMDHAR, SlTrxh, SlPrx, SlGrx, SlNRT2.4, SlNR, SlGS2, and SlNiR decreased after Nstarvation and increased after Nre-supply, which were validated by qRT-PCR. Our results provide abasis for understanding the response of tomato to Ndeficiency and resupply and atheoretical reference for cultivation regulation.