Physiological and Molecular Response of Arabidopsis thaliana (L.) to Nanoparticle Cerium and Indium Oxide Exposure

The effects of cerium oxide (CeO2) and indium oxide (In2O3) nanoparticles (NPs) exposure on Arabidopsis thaliana (L.) Heynh. were investigated. After inoculation in half strength MS medium amended with 0-2000 ppm CeO2 and In2O3 NPs for 25 days, both physiological and molecular responses were evaluated. Exposure at 250 ppm CeO2 NPs significantly increased plant biomass, but at 500-2000 ppm, plant growth was decreased by up to 85% in a dose-dependent fashion. At 1000 and 2000 ppm CeO2 NPs, chlorophyll production was reduced by nearly 60% and 85%, respectively, and anthocyanin production was increased 35-fold. Malondialdehyde (MDA) production, a measure of lipid peroxidation, was unaffected by exposure to 250-500 ppm CeO2 NPs, but at 1000 ppm, MDA formation was increased by 2.5-fold. Exposure to 252000 ppm In2O3 NPs had no effect on A. thaliana biomass and only minor effects (15%) on root elongation. Total chlorophyll and MDA production were unaffected by In2O3 NPs exposure. Molecular response to NP exposure as measured by qPCR showed that both types of elements altered the expression of genes central to the stress response such as the sulfur assimilation and glutathione (GSH) biosynthesis pathway, a series of genes known to be significant in the detoxification of metal toxicity in plants. Interestingly, In2O3 NPs exposure resulted in a 3.84.6-fold increase in glutathione synthase (GS) transcript production, whereas CeO2 NPs yielded only a 2-fold increase. It seems likely that the significantly greater gene regulation response upon In2O3 NPs exposure was directly related to the decreased phytotoxicity relative to CeO2 treatment. The use of NP rare earth oxide elements has increased dramatically, yet knowledge on fate and toxicity has lagged behind. To our knowledge, this is the first report evaluating both physiological and molecular plant response from exposure to these important nanoparticles.