Combined effect of nano-CuO and nano-ZnO in plant-related system: From bioavailability in soil to transcriptional regulation of metal homeostasis in barley

Highlights: • Co-exposure of engineered nanoparticles (ENPs) in soil-plant system was tested. • Zn and Cu content in barley were differed by single and co-treatment with ENPs. • Transcripts of Zn transporters were higher upon nano-ZnO than mixtures of ENPs. • Contrary to ENPs, metal salts down-regulated genes encoding metal homeostasis. • Metallothioneins were up-regulated almost by all treatments in 7-day plants. The co-existence of engineered nanoparticles (ENPs) in the environment is an emerging issue remaining poorly investigated. The present study aimed at analyzing the fate of binary mixtures of CuO and ZnO ENPs in a soil-plant system. The ENPs were singly or jointly dosed into soil at 300 mg kg⁻¹ and aged for 7 and 30 days. To evaluate nano-specific effects, individual and combined treatments of metal salts were also applied. Interactions between ENPs and soil-grown barley Hordeum vulgare were determined in terms of biomass, plant mineral composition as well as expression of genes regulating metal homeostasis (ZIP1,3,6,8,10,14, RAN1, PAA1,2, MTP1, COPT5) and detoxification (MT1–3). The bioavailability of Zn and Cu in bulk soil and in the rooting zone was determined using the 0.01 mol L⁻¹ CaCl₂ extraction. After combined treatment of ENPs, the extractable concentrations of Cu and Zn were lower than upon individual exposure in bulk soil. The opposite tendency was noted for metal salts. Genes related to metal uptake (ZIP) and cellular compartment (PAA2, RAN1) were mostly up-regulated by single rather than combined application of ENPs. The single and joint exposure to metals salts induced the down-regulation of these genes.