Study on oxidative stress and nitric oxide response mechanisms in Gymnodinium sp. under polystyrene microplastic stress

The toxic effects of microplastic pollution on marine microalgae have attracted considerable attention, yet the underlying mechanisms remain unclear. This study used the dinoflagellate Gymnodinium sp. as a model organism to investigate the effects of polystyrene (PS) microplastics at different particle sizes (0.1 and 10 μm) and concentrations (0–50 mg L –1 ) on its growth, photosynthesis, oxidative stress, and nitric oxide (NO) metabolism. Results indicated that PS microplastics significantly inhibited Gymnodinium sp. growth, chlorophyll a (Chl a ) concentration, and photochemical efficiency by 16.4%, 40.3%, and 72.0% respectively, with smaller particles (0.1 μm) exhibiting stronger inhibitory effects. Low concentrations (10–20 mg L –1 ) of microplastics might temporarily enhance algal density and Chl a content, yet exhibited long–term inhibitory effects. Microplastic exposure induced significant reactive oxygen species (ROS) accumulation by 1.96 times, with ROS levels positively correlated to microplastic concentration and exposure duration, indicating oxidative damage as a key mechanism of microplastic toxicity. Microplastic stress markedly elevated nitrate reductase activity (NRA) by 2.86 times and altered NO release patterns–exhibiting NO uptake at low concentrations, shifting to net release at high concentrations. The dynamic changes in NO revealed its dual role in microalgal stress resistance: initially acting as an antioxidant to alleviate stress, but at higher concentrations potentially exacerbating cellular damage. This study elucidates the mechanisms by which microplastics inhibit microalgal growth through physical shading and oxidative stress, and proposes the key regulatory role of NO metabolism in microplastic stress responses, providing a theoretical basis for assessing the ecological risks of marine microplastics.