Sulfur nanoparticles boost watermelon growth and fruit quality by modulating sulfur transport and nutrient...

This study provides the first comprehensive mechanistic investigation demonstrating how sulfur nanoparticles (S NPs) achieve superior agricultural performance over conventional sulfur through coordinated activation of sulfur transport pathways and systemic reprogramming of nutrient homeostasis in watermelon (Citrullus lanatus). This represents the first study to demonstrate such dramatic transcriptional activation of sulfur transport mechanisms by nanomaterials (304.1-fold increase in ClTUA), establishing a novel paradigm for nanoparticle-mediated agricultural enhancement. Under both greenhouse and field conditions, watermelon plants received three concentrations (100, 200, and 300 mg/L) of either S NPs or conventional sulfur through weekly foliar applications. Results demonstrated that 200 mg/L S NPs (SN2) optimally improved photosynthetic capacity, with marked increases in chlorophyll content (24.94 %) and leaf area (59.43 %) compared to controls. SN2 also triggered substantial biomass accumulation through altered source-sink relationships, with 29.06 % and 45.05 % increases in aboveground and underground fresh weight, respectively. Molecular analysis revealed differential expression of sulfur metabolism genes, with dramatic upregulation of the sulfur transport protein gene ClTUA (304.1-fold increase), indicating activated sulfur acquisition pathways. Furthermore, S NPs reprogrammed nutrient homeostasis, increasing Fe (63.2 %), Ca (126.2 %), and P (54.2 %) accumulation in photosynthetic tissues, which supported optimized carbohydrate metabolism in fruits as evidenced by 11.90 % higher sugar content. Physicochemical characterization revealed that S NPs (20-30 nm) with uniform morphology exhibited enhanced bioavailability compared to conventional sulfur due to altered surface chemistry and increased reactivity, as confirmed by FTIR spectroscopy and XRD analysis. These findings elucidate the mechanistic basis for S NPs efficacy, demonstrating their role in activating sulfur transport pathways, reprogramming nutrient acquisition networks, and enhancing photosynthetic efficiency in watermelon.