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Shifts in N and δ15N in wheat and barley exposed to cerium oxide nanoparticles
Citation:
Rico, C., M. Johnson, M. Marcus, AND Christian P Andersen. Shifts in N and δ15N in wheat and barley exposed to cerium oxide nanoparticles. NanoImpact. Elsevier B.V., Amsterdam, Netherlands, 11:156-163, (2018). https://doi.org/10.1016/j.impact.2018.08.003
Impact/Purpose:
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 if ENMs alter nutrient uptake and use in plants, we exposed wheat and barley to CeO2 nanoparticles (NPs), in soil and in solution culture. We hypothesized that CeO2-NPs would alter nitrogen (N) uptake and use, or alter incorporation of stable isotopes of N, which may provide insight into the underlying mechanisms of ENM. We also used two seed types to determine if parental exposure to CeO2-NPs altered growth or nutrition of offspring. The results showed that CeO2-NPs modified the ratio of N isotopes in wheat more than barley. The isotopic changes in soil and in solution indicated that CeO2-NPs may be altering the forms of N taken up, the assimilation of N after uptake, or both uptake and assimilation. There was evidence that parental exposure to CeO2-NPs altered the N contents and concentrations of the offspring, although the differences were small. The study illustrates that CeO2-NPs can alter the nutrient dynamics in plants through a complex set of processes involving root uptake and metabolism. These findings raise important questions on the effects of engineered nanomaterials on nitrogen cycling in the environment, and may lead to a sensitive earlier indicator of ENM exposure in some plant species.
Description:
The effects of cerium oxide nanoparticles (CeO2-NPs) on 15N/14N ratio (δ15N) in wheat and barley were investigated. Seedlings were exposed to 0 and 500 mg CeO2-NPs/L (Ce-0 and Ce-500, respectively) in hydroponic suspension supplied with NH4NO3, NH4+, or NO3−. N uptake and δ15N discrimination (i.e. differences in δ15N of plant and δ15N of N source) were measured. Results showed that N content and 15N abundance decreased in wheat but increased in barley. Ce-500 only induced whole-plant δ15N discrimination (−1.48‰, P ≤ 0.10) with a simultaneous decrease (P ≤ 0.05) in whole-plant δ15N (−3.24‰) compared to Ce-0 (−2.74‰) in wheat in NH4+. Ce-500 decreased (P ≤ 0.01) root δ15N of wheat in NH4NO3 and NH4+ (3.23 and −2.25‰, respectively) compared to Ce-0 (4.96 and −1.27‰, respectively), but increased (P ≤ 0.05) root δ15N of wheat in NO3− (3.27‰) compared to Ce-0 (2.60‰). Synchrotron micro-XRF revealed the presence of CeO2-NPs in shoots of wheat and barley regardless of N source. Although the longer-term consequences of CeO2-NP exposure on N uptake and metabolism are unknown, the results clearly show the potential for ENMs to interfere with plant metabolism of critical plant nutrients such as N even when toxicity is not observed.
