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Molecular and physiological responses to titanium dioxide and cerium oxide nanoparticles in Arabidopsis
Tumburu, L., C. Andersen, P. Rygiewicz, AND J. Reichman. Molecular and physiological responses to titanium dioxide and cerium oxide nanoparticles in Arabidopsis. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 36(1):71-82, (2017).
Engineered nanoparticles (ENMs) have been recognized as valuable components of new technologies and are currently being used in a variety of consumer products due to their unique physical, chemical, and electrical properties. The properties that make these particles functionally unique also may influence their toxicity to organisms in ecosystems. CSS’s Emerging Materials research is designed to identify potential adverse effects of these materials in the environment, including toxicity to plants and animals. Ideally EPA would like to understand mechanisms of response to ENMs in order to develop predictive tools to evaluate new nanomaterials as they are developed. To gain better understanding of mechanisms of response in plants following metal nanoparticle exposure, WED scientists exposed Arabidopsis thaliana, a common mustard plant with a well-documented genome, to nano titanium dioxide (nTiO2) or nano cerium oxide (nCeO2). Microarray analyses confirmed that both nCeO2 and nTiO2 significantly altered gene expression of important metabolic pathways in both leaves and roots, however the two particles largely affected different metabolic pathways. The changes in gene expression did not always lead to changes in growth, indicating that plants may be able to avoid adverse effects through compensatory pathways. The different responses to nCeO2 and nTiO2 suggest that the two particles have different modes of action in plants. Ongoing research will provide additional understanding on the early mechanistic changes in response to ENMs, with the goal of developing predictive tests for evaluating new materials as they are developed.
- Changes in tissue transcriptomes and productivity of Arabidopsis thaliana were investigated during exposure of plants to two widely-used engineered metal oxide nanoparticles, titanium dioxide (nano-titanium) and cerium dioxide (nano-cerium). Microarray analyses confirmed that exposure to either nanoparticle altered the transcriptomes of rosette leaves and roots, with comparatively larger numbers of differentially expressed genes (DEGs) found under nano-titania exposure. Nano-titania induced more DEGs in rosette leaves, whereas roots had more DEGs under nano-ceria exposure. MapMan analyses indicated that while nano-titania up-regulated overall and secondary metabolism in both tissues, metabolic processes under nano-ceria remained mostly unchanged. Gene enrichment analysis indicated that both nanoparticles mainly enriched ontology groups such as responses to stress (abiotic and biotic), and defense responses (pathogens), and responses to endogenous stimuli (hormones). Nano-titania specifically induced genes associated with photosynthesis, whereas nano-ceria induced expression of genes related to activating transcription factors, most notably those belonging to the ethylene responsive element binding protein family. Interestingly, there were also increased numbers of rosette leaves and plant biomass under nano-ceria exposure, but not under nano-titania. Other transcriptomic responses did not clearly relate to responses observed at the organism level. This may be due to functional and genomic redundancy in Arabidopsis which may mask expression of morphological changes, despite discernable responses at the transcriptome level. Additionally, transcriptomic changes often relate with transgenerational phenotypic development, hence it may be productive to direct further experimental work to integrate high-throughput genomic results with longer-term changes in subsequent generations.