Keywords: 
• zinc oxide /
• nanoparticle /
• wheat /
• toxicity /
• imbibition phase /
• sprout phase /
• budding phase

Abstract: Although zinc oxide nanoparticles (ZnO NPs) are known to be one of the most widely used nanomaterials, more and more researches have revealed that ZnO NPs may have potential biological risks. However, the dependence of the toxicity of ZnO NPs on the germination phases of seeds has not been investigated until the present time. To address this issue, water-cultured wheat (Triticum aestivum L) seeds were selected as the testing seeds, and were treated with ZnO NPs at three different germination phases, including the imbibition phase, the sprout phase and the budding phase. The results showed that ZnO NPs could be toxic to wheat seeds at all these three germination phases, but the significance of the toxicity at each phase was quite different (P<0.05). When treated with 60 mg·L^-1 ZnO NPs suspension, the inhibition rate of wheat roots by ZnO NPs was 37.8%, 80.2% and 95.7% at imbibition phase, sprout phase and budding phase, respectively; at sprout phase and budding phase, the toxicity of ZnO NPs showed an obvious concentration dependence, and higher concentration resulted in higher toxicity. The above results are of great significance for a comprehensive evaluation of the toxicity of ZnO NPs.