Calcium oxide nanoparticle and jasmonic acid interplay drives cucumber salt tolerance: Insights from mechanistic,...

Global initiatives are advancing swiftly to address the rapidly growing issue of soil salinisation. No substantial data exists to elucidate the associated roles of Fluorescein-isothiocyanate (FITC) labelled calcium oxide nanoparticles (nCao) and jasmonic acid (JA) in enhancing the salt tolerance of cucumber. Investigating the effect of FITC-nCaO and JA improving salt tolerance in cucumber to expand the toolbox of nanomaterials for nano-enabled salt tolerance in cucumber is the primary aim of this study. The NaCl (120 mM) -stressed seedlings (two weeks after transplanting) supplemented with 90 mg L^-1 nCaO and 45 μM JA at 4-leaf stage, showed a substantial decrease (50 %) in Na⁺/K⁺ ratio. This treatment also significantly enhanced fresh shoot biomass (123 %), root biomass (125 %), Fv/Fm (36 %), chlorophyll content (21 %), mineral uptake, osmolyte accumulation, and cellular redox homeostasis. Confocal laser scanning microscopy established FITC-tagged nCaO penetration from leaves epidermal cells supported by scanning electron microscopy illustrated better root ultracellular anatomy and leaf stomatal functionality, underpinning improved gaseous exchange characteristics and photosynthetic performance under salt stress. Furthermore, co-treatment with FITC-nCaO and JA reduced oxidative damage, as evidenced by significant reductions in hydrogen peroxide (62 %), superoxide anion (45 %), electrolyte leakage (47 %), and malondialdehyde (52 %). These observations are justified by NBT staining visuals, upregulated antioxidant enzyme activity, and relative expression of antioxidant genes by qRT-PCR assay. Overall, the concurrent application of FITC-nCaO with JA restored the salt-induced damages in cucumbers by improving morpho-physiological attributes, relative gene expression, and preserving the ultracellular structure of organelles. Thereby, these simultaneous foliar treatments are not only encouraged as an effective strategy to protect cucumbers from salt stress damage but also minimize the risk of nanoparticle dispersion into environmental compartments via soil application.