Unraveling the Mechanistic Basis of Nanoparticle Mediated Antioxidant Defense under Salinity Stress

Abstract

Soil salinity represents one of the most pervasive abiotic stresses, constraining global agricultural productivity, affecting over 1.4 billion hectares of arable land worldwide. The emergence of nanoparticle (NP)-based agronomic interventions has opened a compelling new frontier in stress physiology research, offering targeted, low-dose strategies to bolster plant defense machinery. This review critically examines the mechanistic basis by which various nanoparticles- including zinc oxide (ZnO), silicon dioxide (SiO₂), titanium dioxide (TiO₂), cerium oxide (CeO₂) and carbon-based nanomaterials-modulate reactive oxygen species (ROS) homeostasis, enzymatic antioxidant networks, osmoprotectant accumulation and ion transport dynamics in crop plants exposed to salinity stress. Despite the rapid growth of this field, a critical research gap considering the mechanistic hierarchy governing NP-mediated antioxidant enhancement remains poorly defined and it is unclear which molecular targets are primary drivers versus secondary consequences of improved salinity tolerance. This raises a pivotal question, if nanoparticles genuinely reprogram plant redox homeostasis at the transcriptional and enzymatic level or they primarily relieve osmotic and ionic constraints that otherwise suppress constitutive antioxidant capacity. Addressing this distinction is essential for rational nano-agronomic design. Hence, this review is the first to integrate nanoparticle-mediated regulation of ROS homeostasis, enzymatic antioxidant networks, proline metabolism, and ion transport into a unified mechanistic framework for salinity tolerance, while critically addressing dose-dependent phytotoxicity, NADPH availability and redox-sensitive transcription factor signaling.