Salinity stress mitigation in tomato (Solanum lycopersicum L.): mechanisms, impacts and copper nanoparticle based solution

Salinity stress is a major abiotic factor that severely limits global crop productivity. It disturbs plant water relations, ion homeostasis and redox balance, leading to reduced plant growth and productivity. Conventional practices have only partially alleviated these constraints, especially in the rapidly expanding salt-affected areas, driven by climate change and unsustainable irrigation practices. In this context, copper-based nanoparticles (Cu-NPs) have emerged as promising nano-agrochemicals, capable of modulating multiple stress-responsive pathways. This review summarizes the current knowledge on the morpho-physiological, biochemical and molecular mechanisms implicated in salinity tolerance in tomato and critically evaluates how Cu based nanoparticles modulate cellular homeostasis to improve salt resilience. Evidence from physiological, biochemical and ionic studies indicates that Cu based nanoparticles stabilize cellular metabolism under saline conditions, by strengthening antioxidant defense, improve Na + exclusion and K + retention and protect photosynthetic performance. Proteomic investigations further reveal that in Cu-NP-treated tomato plants, the aforementioned cellular alternations are coordinated through stress signaling proteins and involve energy metabolism. Thus, providing a mechanistic basis for the observed phenotypic benefits. Genotype as well as concentration dependent responses emphasize that Cu-NP efficacy is maximized at intermediate doses under moderate stress, while excessive application can trigger copper toxicity and redox imbalance. The review also discusses potential environmental risks, regulatory gaps and standardization challenges associated with deployment of copper-based nanoparticles under field conditions. By integrating multi-scale evidence, the review provides a conceptual framework for rationally designing Cu-NP based interventions and identifies key research priorities for their safe and effective use in tomato cultivation.