Integrated transcriptomic and metabolomic analyses reveal the effects of nanoplastics on root development, oxidative stress, and metabolic pathways in different apple rootstock varieties

Microplastics, as a novel environmental pollutant, are now widely distributed in agricultural soils globally and pose a threat to plant growth and development. Within apple orchards, the ageing and degradation of agricultural plastic films leads to soil microplastic contamination, inhibiting the growth of apple trees. This study employed apple rootstocks 'M9' and 'B9' alongside the apple cultivar 'Gala3', treating them with polystyrene nanoplastics (PS-NPs) at varying concentrations (0, 5, 10, 20, 40, 80 mg/L). Results indicate that low PS-NP concentrations promote apple seedling growth, whereas high concentrations inhibit root development and growth while reducing antioxidant capacity. Sensitivity to PS-NPs varies among genotypes, with 'M9' exhibiting the lowest sensitivity and 'Gala3' the highest. Based on these phenotypic differences, transcriptomic and metabolomic sequencing was performed on these two cultivars. Integrated transcriptomic-metabolomic analysis revealed that PS-NPs disrupted zeatin metabolic homeostasis by upregulating CKX gene and downregulating UGT73C gene. This accelerated the metabolism of active zeatin (e.g., trans-zeatin) and leading to dihydrozeatin (DHZ) accumulation, thereby impairing the activation capacity of the antioxidant defence system and ultimately exacerbating oxidative damage. These findings establish a foundation for systematic investigation into the molecular mechanisms underlying apple responses to nanoplastics, offering novel perspectives for future crop production and environmental safety.