Titanium Dioxide Nanoparticles Promote Root Growth by Interfering with Auxin Pathways in Arabidopsis thaliana

Abstract

TiO2 nanoparticles (nano-TiO2) are widely used in the world, and a considerable amount of nano-TiO2 is released into the environment, with toxic effects on organisms. In the various species of higher plants, growth, including seed germination, root elongation, and biomass accumulation, is affected by nano-TiO2. However, the underlying molecular mechanisms remain to be elucidated. In this study, we observed that nano-TiO2 promoted root elongation in a dose-dependent manner. Furthermore, we found that nano-TiO2 elevated auxin accumulation in the root tips of the auxin marker lines DII-VENUS and DR5:: GUS, and, correspondingly, quantitative real-time PCR analysis revealed that nano-TiO2 increased the expression levels of auxin biosynthesis- and transportrelated genes. GFP fluorescence observation using transgenic PIN2-GFP indicated that nano-TiO2 promoted root growth by inducing PIN2 accumulation. Thus, we propose that nano-TiO2 promote root growth in Arabidopsis thaliana by altering the expression levels of auxin biosynthesis- and transport-related genes.