Strigolactone-biosilica nanoparotectants regulate vacuolar sequestration, phytohormones and oxidative metabolism to enhance cadmium tolerance in Brassica napus.

Cadmium (Cd) contamination severely impairs plant productivity, necessitating effective mitigation strategies. This study investigated the efficacy of strigolactone-conjugated silica nanoparticle (SL-SiO2 NPs) in regulating Cd-toxicity in Brassica napus L. Foliar application of SL-SiO2 NPs decreased Cd accumulation (28-22 % in leaves and roots) through enhanced cell wall sequestration, while improving plant height and leaf area. These improvements correlated with enhanced photosynthetic efficiency PSII (35 %) and nutrient accumulation. Secondary metabolite analysis revealed that combined treatments of SL-SiO2 NPs and Cd altered the plant metabolite profile, with acetate compounds showing the most pronounced effect across treatments. PCA analysis demonstrated clear separation of treatment groups along two principal components that together explained 90 % of the total variance. Subcellular analysis revealed that SL-SiO2 NPs enhanced cell wall binding capacity for Cd (41-50 %), reducing organelle accumulation and facilitating vacuolar sequestration. The treatment decreased H2O2, O2•- and MDA levels by modulating genes associated with antioxidant enzymes (SOD, POD) and chlorophyll biosynthesis (BnaCHLG, BnaCAO). SL-SiO2 NPs protected cellular ultrastructure and maintained membrane integrity. These findings demonstrate that SL-SiO2 NPs effectively mitigate Cd-toxicity through improved metabolic responses, photosynthetic efficiency and antioxidant defense mechanisms in metal-contaminated conditions.