Molecular characterization and transcriptional response of Lactuca sativa seedlings to co-exposure to graphene nanoplatelets and titanium dioxide nanoparticles.

The widespread use of nanomaterials in agriculture may introduce multiple engineered nanoparticles (ENPs) into the environment, posing a combined risk to crops. However, the precise molecular mechanisms explaining how plant tissues respond to mixtures of individual ENPs remain unclear, despite indications that their combined toxicity differs from the summed toxicity of the individual ENPs. Here, we used a variety of methods including physicochemical, biochemical, and transcriptional analyses to examine the combined effects of graphene nanoplatelets (GNPs) and titanium dioxide nanoparticles (TiO 2 NPs) on hydroponically exposed lettuce (Lactuca sativa) seedlings. Results indicated that the presence of GNPs facilitated the accumulation of Ti as TiO 2 NPs in the seedling roots. Combined exposure to GNPs and TiO 2 NPs caused less severe oxidative damage in the roots compared to individual exposures. Yet, GNPs and TiO 2 NPs alone and in combination did not cause oxidative damage in the shoots. RNA sequencing data showed that the mixture of GNPs and TiO 2 NPs led to a higher number of differentially expressed genes (DEGs) in the seedlings compared to exposure to the individual ENPs. Moreover, the majority of the DEGs encoding superoxide dismutase displayed heightened expression levels in the seedlings exposed to the combination of GNPs and TiO 2 NPs. The level of gene ontology (GO) enrichment in the seedlings exposed to the mixture of GNPs and TiO 2 NPs was found to be greater than the level of GO enrichment observed after exposure to isolated GNPs or TiO 2 NPs. Furthermore, the signaling pathways, specifically the "MAPK signaling pathway-plant" and "phenylpropanoid biosynthesis," exhibited a close association with oxidative stress. This study has provided valuable insights into the molecular mechanisms underlying plant resistance against multiple ENPs. [Display omitted] • GNPs facilitated the accumulation of Ti as TiO 2 NPs in the roots of lettuce seedlings. • Mixtures of GNPs and TiO 2 NPs caused less severe oxidative damage to seedling. • GNPs and TiO 2 NPs in mixture increased the amount of differentially expressed genes. • MAPK signaling pathway/phenylpropanoid biosynthesis contributed most to oxidative stress. • Seedling roots were more responsive to the combination of GNPs and TiO 2 NPs than the shoots. [ABSTRACT FROM AUTHOR]

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