Effects of polystyrene nanoplastics (PSNPs) on the physiology of Allium sativum L.: Photosynthetic pigments, antioxidant enzymes, phytohormones, and nutritional quality

Abstract

Nanoplastics (NPs) arouse increasing attention recently. Many studies have shown possible negative effects on plants exposed to NPs, but more data are needed on various species of plants to elucidate the potential phytotoxicity mechanisms of NPs. In this work, a pot experiment was conducted to analyze toxicity induced by polystyrene nanoplastics (PSNPs; particle size, 75.10 nm) at diverse doses (0.05, 0.1, 0.25, 0.5, 1.0 mg/g dry soil weight) to seedlings of garlic (Allium sativum L.). The photosynthetic pigments, antioxidant enzyme activities, common phytohormones and styrene contents, and nutritional quality of leaves of A. sativum seedlings were determined. Results showed that the toxic effects of PSNPs on plants at 42 days after exposure were stronger than those at 28 days. Chlorophyll a, chlorophyll b, as well as carotenoids levels within A. sativum leaves treated with PSNPs for 42 days decreased, with the highest decreasing rates of 40.22%, 41.29%, and 27.38%, respectively. The malondialdehyde (MDA) level within A. sativum leaves was noticeably up-regulated at 0.5 and 1.0 mg/g of PSNPs. Furthermore, the guaiacol peroxidase (POD) and catalase (CAT) activities and the abscisic acid (ABA) contents increased significantly with increasing the concentrations of PSNPs. After exposure for 42 days, allicin, soluble sugar and soluble protein levels decreased with increasing the concentration of PSNPs. The highest styrene content in leaves of A. sativum was obtained for the treatment group of the 0.5 mg/g PSNPs, showing an increase of 23.73% relative to control. Collectively, PSNPs were translocated into the leaves of A. sativum from roots, significantly affected the photosynthetic pigments contents, and significantly induced oxidative stress in A. sativum. Furthermore, high doses of PSNPs exposure impaired the A. sativum’s nutritive quality. These research results can provide basic data for accurately evaluating the ecological toxicity of NPs on crops.