Polyethylene terephthalate nanoplastics affect potassium accumulation in foxtail millet (Setaria italica) seedlings

Background: As modern industrial activities have advanced, the prevalence of microplastics and nanoplastics in the environment has increased, thereby impacting plant growth. Potassium is one of the most crucial nutrient cations for plant biology. Understanding how polyethylene terephthalate (PET) treatment affects potassium uptake will deepen our understanding of plant response mechanisms to plastic pollution.

Results: In this study, we examined the impact of PET micro- and nanoplastics on foxtail millet seedling growth and potassium accumulation. Additionally, we measured reactive oxygen species (ROS) production, antioxidant enzyme activities, and the expression levels of the corresponding enzyme-encoding genes. Our findings indicated that the germination and seedling growth of foxtail millet were not significantly affected by exposure to PET plastics. However, the ROS levels in foxtail millet increased under these conditions. This increase in ROS led to the upregulation of several genes involved in K⁺ uptake and transport (SiHAK1, SiHAK2, SiAKT2/3, SiHKT2;2, SiHKT1;1, SiGORK, and SiSKOR), thereby increasing K⁺ accumulation in foxtail millet leaves. Further research revealed that higher K⁺ concentrations in plant leaves were correlated with increased expression of the antioxidant-related genes SiCAT1, SiPOD1, and SiSOD3, as well as increased activities of the corresponding antioxidant enzymes. This response helps mitigate the excessive accumulation and damage caused by ROS in plant cells after PET nanoplastic treatment, suggesting a potential stress response mechanism in foxtail millet against nanoplastic pollution.

Conclusions: Our research indicates that PET nanoplastic treatment induces the expression of genes related to K⁺ uptake in foxtail millet through ROS signaling, leading to increased K⁺ accumulation in the leaves. This process mitigates the ROS damage caused by PET nanoplastic treatment by increasing the expression and activity of genes encoding antioxidant enzymes. The present research has unveiled the K⁺ accumulation-related response mechanism of foxtail millet to PET nanoplastic treatment, contributing significantly to our understanding of both the potassium absorption regulation mechanism in plants and the broader impact of plastic pollution on agricultural crops. This discovery not only highlights the complexity of plant responses to environmental stressors but also underscores the importance of considering such responses when evaluating the ecological and agricultural implications of plastic pollution.