Role of nitrate reductase, nitric oxide, and S-nitrosylation in salinity stress in plants: A review.

Salt stress is a critical environmental factor that restricts plant growth and agricultural production. Nitrate Reductase (NR) is a core enzyme in plant nitrogen metabolism. Interestingly, studies have shown that the expression and activity of NR are tissue-specific, which may provide new targets for improving the salt tolerance of crops through genetic engineering. It influences plant salt tolerance through the regulation of nitrogen metabolism, osmotic regulation, and antioxidant defense. This review synthesizes emerging insights into how NR orchestrates plant salt tolerance through three interconnected mechanisms: fine-tuning of nitrogen metabolism, mediating Nitric Oxide (NO) production, and regulating protein S-nitrosylation. We propose a novel regulatory axis: NR → NO3- reduction → NO → S-nitrosylation, which integrates metabolic and signaling pathways to enhance osmotic adjustment, antioxidant defense, ion homeostasis, and hormonal crosstalk. However, the existing evidence only suggests an association for this integration pathway and the key causal relationship still requires further verification. We also discuss unresolved spatiotemporal dynamics of NR-derived NO and its downstream modifications, offering new perspectives for engineering salt-tolerant crops through manipulation of NR-mediated networks.