Influences of zinc oxide nanoparticles on Allium cepa root cells and the primary cause of phytotoxicity
Zinc oxide nanoparticles (ZnO-NPs) are widely used in consumer products, which have raised concerns about their impact on the human health and environment. In this study, Allium cepa were treated with 5 and 50 μg/mL ZnO-NPs solutions for 12, 24, and 36 h, respectively. The cytotoxic and genotoxic effects of ZnO-NPs in root meristems of Allium cepa cells were characterized by cell membrane integrity, metabolic activity, reactive oxygen species (ROS) accumulation, DNA damage, chromosome aberration, and cell cycle progression. Substantially elevated Zn levels were observed in the cytoplasmic and nuclear fractions, and the accumulation of zinc in the nuclear fraction (up to 9764 μg/g) was one magnitude greater than that in the cytoplasm (up to 541 μg/g). The complexation of Zn2+ with diethylene triamine pentacetic acid (DTPA) was performed to explicate the respective contribution of insoluble particles or Zn2+ to ZnO-NPs toxicity. We found that the inhibition of root growth accounted for 24.2% or 36.1% when the plants were exposed to Zn2+ that released from 5 or 50 μg/mL of ZnO-NPs for 36 h, respectively, whereas the exposure to 5 or 50 μg/mL of insoluble particles resulted in 75.8% or 63.9% of inhibition, respectively. These findings demonstrated that adverse effects exerted not just by Zn2+ released from ZnO-NPs, but also directly from the nanoparticles. These findings contribute to a better understanding of ZnO-NPs cytotoxicity and genotoxicity in plant cells and provide valuable information for further research on the phytotoxic mechanisms of ZnO-NPs.
Substantially elevated Zn levels were observed in the cytoplasmic and nuclear fractions of A. cepa roots.
ZnO-NPs inhibited plant growth and induced severe cytotoxicity and genotoxicity.
The toxicity of ZnO particles is higher than zinc ions released from them.
KeywordsZinc oxide nanoparticles Allium cepa DTPA Phytotoxicity
This research was supported by the National Natural Science Foundation of China (Grant no. 31670266), the Guangdong Pearl River Scholar Funded Scheme (2012), the Science and Technology Program of Guangzhou, China (Grant no. 2014J4100053), and the Natural Science Foundation of Guangdong Province, China (Grant no. 2017A030313115) to Prof. Shaoshan Li. This work also received support from the Natural Science Foundation of China (Grant no. 41701572) and the Chinese Postdoctoral Science Foundation (Grant no. 2017M612684).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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