Metallic nano-oxides as foliar tools for improving oil crop traits and compositional bioactivity

The Sunflower (Helianthus annuus L.) is an oil-bearing plant of the Asteraceae family. The oil quality of sunflower can be steered by nano-oxide foliar inputs, but the exact reasons for these physiological and chemical consequences still remain unclear. We evaluated the impact of 20–80 ppm concentrations of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles applied to the leaves and roots of sunflower from germination to flowering. The nano-dose was implemented twice a month and tracked morphological growth traits, chlorophyll and protein, yield, and seed-oil composition by GC–MS. The ZnO improved vegetative performance across doses, increasing leaf number and stem/petiole diameter and advancing bud initiation. The TiO₂ produced a mild gain at low concentrations but depressed several traits at higher doses. The oil chemistry diverged accordingly as ZnO favored longer-chain and oxygenated esters (for example, ethyl linoleate, methyl stearate), whereas TiO₂ increased medium-chain fatty acids together with tocopherol-linked species and squalene. The higher chlorophyll/protein under ZnO coincided with enrichment of longer-chain esters, while TiO₂-linked chlorophyll loss paired with a shift toward antioxidant-associated lipids. The research reveals that ZnO as a micronutrient source maintains photosynthetic capacity and supports elongation/esterification in seed oils. The photoactive TiO₂, under light conditions raises oxidative cues that redirect carbon toward isoprenoid-based antioxidant defenses. ZnO nanoparticles act as a sustained source of zinc ions, enabling continuous nutrient availability over time under concentration-dependent application conditions. This provides a practical lever to shift sunflower oil toward longer-chain esters, whereas TiO₂ requires careful light management to avoid plant stress and an undesired shift in the oil profile. Graphical abstract