Melatonin Defends Against the Oxidative Stress by Preventing the Uptake of Nanoplastics and Activating the Antioxidant System in <i>Paeonia ostii</i>

As emerging pollutants of global concern, the toxicity of polystyrene nanoplastics (PS-NPs) in plants has received widespread attention, but little is known about how to alleviate their adverse impacts on wood plants. In Paeonia ostii, PS-NPs could be uptood by roots, transported and accumulated in stems and leaves, and induced oxidative stress and negatively affected plant growth. Exogenous melatonin application has for the first time shown to reduce the cell wall porosity to prevent PS-NPs from entering the cells via inhibiting the expression of genes associated with expansins, ultimately decreasd PS-NPs accumulation. And exogenous melatonin also activated the antioxidant system to scavenge reactive oxygen species (ROS) and alleviated the adverse impacts of PS-NPs on plant growth. Moreover, increasing endogenous melatonin by overexpressing N-acetylserotonin-O-methyltransferase gene obtained the similar results as mentioned above. And the transgenic plants uptook and accumulated relatively lower levels of PS-NPs by reducing the cell wall porosity, and induced lower ROS accumulation by activating the antioxidant system. Collectively, these results suggested that melatonin could defend against the oxidative stress caused by PS-NPs via preventing their uptake and activating the antioxidant system in P. ostii, which highlighted that melatonin can be used to protect plants in the nanoplastic-polluted environments.