Stomatal geometric remodeling and stress alleviation in grapevines treated with chitosan–arginine nanoparticles under Salinity

Salinity could reduce grapevine productivity, impairing physiological performance, nutrient balance, and cellular integrity. This study evaluated the potential of arginine anchored chitosan nanoparticles (CTS-Arg NPs), arginine (Arg), chitosan (CTS) and chitosan–arginine combination (CTS-Arg) to mitigate stress damage and modulate stomatal geometry in grapevine. Treatments including CTS (0.1% w/v), Arg (0.5 and 1 mM), CTS-Arg (0.5 and 1 mM), and CTS-Arg NPs (0.5 and 1 mM) were applied under salinity levels (0, 50, and 100 mM NaCl). Salinity caused significant reductions ( p < 0.01) in chlorophyll a (Chl a ), chlorophyll b (Chl b ), total chlorophyll content (Total Chl), Fv/Fm, Fv/Fo, potassium (K), and (p < 0.01) in SPAD values, phosphorus (P) compared to control. In contrast, salinity significantly ( p < 0.05) increased proline, total phenolic compounds, flavonoids, malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ), electrolyte leakage (EL), glycine betaine (GB),protein content, sodium (Na) accumulation, and the activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and phenylalanine ammonia-lyase (PAL) compared to control. Application of CTS-Arg NPs, particularly at 1 mM, significantly ( p < 0.01) alleviated salinity-induced damages by improving physiological characteristics compared with salinity-stressed untreated plants. Furthermore, geometric morphometric analysis revealed that salinity stress promoted stomatal rounding, whereas CTS-Arg NP treatment induced a considerable shift toward ovality form, indicating stomatal remodeling associated with enhanced physiological efficiency. Overall, CTS-Arg NPs outperformed CTS, Arg, and their non-nano combinations under both control and salinity conditions, highlighting their potential as an effective nano-enabled strategy for improving grapevine tolerance to salinity stress. • CTS‑Arg nanoparticles enhanced grapevine tolerance to salinity stress (p < 0.05) • CTS‑Arg NPs improved photosynthetic efficiency and antioxidant enzyme activity • Salinity stress induced stomatal rounding, while CTS‑Arg NPs promoted oval geometry • Nano‑delivered arginine outperformed CTS, Arg, and CTS‑Arg under salinity • Stomatal geometric remodeling was linked to improved physiological performance