Titanium Dioxide Nanoparticles Alleviate Tetracycline Toxicity to Arabidopsis thaliana (L.)

Arabidopsis thaliana (L.) Heynh. was used as a model plant to investigate the biochemical and molecular response upon coexposures to tetracycline (TC) and titanium oxide nanoparticles (TiO2 NPs). Results showed that 1 mg/L TC severely reduced A. thaliana biomass by 33.3% as compared with the control; however, the presence of 50 and 100 mg/L TiO2 NPs alleviated TC toxicity, increasing fresh biomass by 45% and 28%, respectively, relative to the TC alone treatment. The presence of TC notably decreased Ti accumulation in both shoots and roots. Antioxidant enzyme activity, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD), in A. thaliana shoots and roots indicated that TC significantly increased the activity of reactive oxygen species (ROS) scavengers. However, in the coexposure treatments, TiO2 NPs reduced antioxidant enzyme activity back to the control levels. The relative expression of genes encoding sulfur assimilation and glutathione biosynthesis pathways was separately measured in shoots and roots. Interestingly, the relative expressions of adenylytransferase (APT), adenosine-5'-phosphosulfate reductase (APR), and sulfite reductase (SiR) in the roots across all three treatments (TC alone, TiO2 NPs alone, and TC X TiO2 NPs treatment) were 2-3.5-fold higher than the control. The expression of gamma-glutamylecysteine synthetase (ECS) and glutathione synthetase (GS) was increased in A. thaliana treated with either TiO2 NPs or TC alone. At harvest, almost 93% reduction of the pod biomass was evident in the TC alone treatment as compared with the control; however, TiO2 NPs increased the pod biomass by 300% in the coexposed plants relative to the TC alone treatment. These findings provide important information for understanding the interactions of metal-based NPs and cocontaminants such as antibiotics in plant systems.