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Effect of nTiO2 and nCeO2 nanoparticles on gene expression, germination, and early development in plants
Citation:
Andersen, C., G. King, Milt Plocher, M. Storm, P. Rygiewicz, L. Tumburu, AND J. Reichman. Effect of nTiO2 and nCeO2 nanoparticles on gene expression, germination, and early development in plants. International Congress on Safety of Engineered Nanoparticles and Nanotechnologies, Helsinki, FINLAND, April 12 - 15, 2015.
Impact/Purpose:
Nanoparticles have been incorporated into numerous consumer products and are likely to reach the terrestrial environment in significant concentrations, yet little is known about their potential toxicity to terrestrial plants. Standard testing protocols for testing the toxicity of new materials are based on those developed for chemicals in solution, and may not be appropriate for assessing the toxicity of nanoparticles. To examine the effects of TiO2 and CeO2 on terrestrial plants, 10 agronomic plant species were exposed to different concentrations of each nano particle and followed to examine effects on germination and early seedling development. An additional species, Arabidopsis thaliana, was examined to determine if nanoparticle exposure altered gene expression, and whether shifts in gene expression were consistent with changes in germination and early seedling development. Both positive and negative effects on germination and early growth were observed in response to the nanoparticle suspensions, depending on the species. Changes in gene expression also were observed in response to both particles, and many of the changes were consistent with the observed changes in early growth and development. However, there were also significant differences in gene expression in response to the different particles, indicating that the mode of action of TiO2 may differ from that of CeO2. The germination results indicate that there may be small, early-stage changes associated with nanoparticle exposure in plants, and these changes may influence the timing of specific developmental events during their life cycle. Overall, the results indicate that many of the physiological changes occurring in response to nanoparticle exposure may not be identified through the traditional germination test, and that a more robust test may be needed to fully assess the effects of nanoparticle exposure to terrestrial plants.
Description:
Ten agronomic plant species and Arabidopsis thaliana were exposed to different concentrations of the metal oxide nanoparticles (NPs) TiO2 or CeO2 (0 - 1000 mg L-1) and monitored to examine effects on germination rate and early seedling development. Endpoints measured included germination percentage, cotyledon emergence, and seedling root length. Nine and 5 of the 11 species responded to nTiO2 and nCeO2, respectively. Both positive and negative effects on germination and early growth were observed in response to the nanoparticle suspensions, depending on the species. In A. thaliana, gene expression was quantified along with germination and early seedling development. Genomic responses to both particles included upregulation in genes involved in oxidative stress, and also those involved in early growth and development. But unlike nTiO2, exposure to nCeO2 resulted in upregulation of genes associated with various transporters, and downregulation rather than upregulation of several genes associated with photosynthesis. The specific differences in gene expression in response to nTiO2 and nCeO2 suggest that modes of action for the two metal oxide NPs may be different. The subtle effects on germination rate and early seedling growth indicate that the two NPs may influence early-stage processes that alter specific developmental events during a plants life cycle. Finally, our results indicate that the standard germination test, which is commonly used for toxicity screening of new materials, may not be adequate to identify the subtle physiological changes that occur in terrestrial plants in response to nanoparticle exposure.