Transcriptome alterations in zebrafish gill after exposure to different sizes of microplastics.

Most studies on microplastics (MPs) focused on gut, liver, and brain, and MPs toxicity was size-dependent, but less has been reported on gill. Here, zebrafish were exposed to three sizes of MPs (45-53 µm, 90-106 µm, and 250-300 µm). Next, comparative transcriptome analysis and determination of physiological indices were performed in zebrafish gills to elucidate the size-associated toxicity of MPs to fish gills. Compared with the control, 60, 344, and 802 differentially expressed genes (DEGs) were identified after exposure to 45-53 µm, 90-106 µm, and 250-300 µm MPs for 5 days, respectively. More DEGs in treatment with bigger MPs suggested that bigger MPs might induce more changes in zebrafish gills than smaller ones. These DEGs were significantly enriched in the FoxO signaling, cellular senescence, circadian rhythm and p53 signaling pathways. Besides, 90-106 µm and 250-300 µm MPs treatments inhibited the cell cycle and prevented the apoptosis. The GSH content significantly increased after MPs exposure, suggesting the induction of oxidative stress. AChE and Na+/K+-ATPase activities were significantly lowered in all MPs treatments than in the control, suggesting the inhibition of neurotransmission and ion regulation. These changes might negatively influence the normal functioning of gills, such as osmoregulation, ion regulation, and respiration.

The time-dependent variations of zebrafish intestine and gill after polyethylene microplastics exposure.

Microplastics (MPs) are common environmental contaminants that present a growing health concern due to their increasing presence in aquatic and human systems. However, the mechanisms behind MP effects on organisms are unclear. In this study, zebrafish (Danio rerio) were used as an in vivo model to investigate the potential risks and molecular mechanisms of the toxic effects of polyethylene MPs (45-53 µm). In the zebrafish intestine, 6, 5, and 186 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In the gills, 318, 92, and 484 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In both the intestine and the gills, Gene Ontology (GO) annotation showed that the main enriched terms were biological regulation, cellular process, metabolic process, cellular anatomical entity, and binding. KEGG enrichment analysis on DEGs revealed that the dominant pathways were carbohydrate metabolism and lipid metabolism, which were strongly influenced by MPs in the intestine. The dominant pathways in the gills were immune and lipid metabolism. The respiratory rate of gills, the activity of SOD and GSH in the intestine significantly increased after exposure to MPs compared with the control (p < 0.05), while the activity of SOD did not change in the gills. GSH activity was only significantly increased after MP exposure for 5 days. Also, the MDA content was not changed in the intestine but was significantly decreased in the gills after MP exposure. The activity of AChE significantly decreased only after MPs exposure for 5 days. Overall, these results indicated that MPs pollution significantly induced oxidative stress and neurotoxicity, increased respiratory rate, disturbed energy metabolism and stimulated immune function in fish, displaying an environmental risk of MPs to aquatic ecosystems.

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To get an optimal mode of irrigation and nitrogen supply for table grape production in North China, a pot experiment was conducted to investigate the effects of different irrigation modes and N application rates on dry matter accumulation and distribution, yield, water use efficiency, and nitrogen use efficiency of table grape. The irrigation modes included conventional drip irrigation (CDI, with sufficient irrigation), alternate partial root-zone drip irrigation (ADI, with 50% amount of the irrigation water of CDI) and fixed partial root-zone drip irrigation (FDI, with 50% amount of the irrigation water of CDI). The nitrogen application rates were set at 0.4 (N1), 0.8 (N2) and 1.2 (N3) g·kg-1 dry soil. The results showed that compared with CDI, ADI and FDI reduced new shoot pruning amount by 34.8% and 11.2%, respectively. New shoot pruning amount increased with increasing N application rates, being highest under CDIN3. Dry matter accumulation of ADI was the highest, being 5.1% and 12.8% higher than CDI and FDI. Dry matter accumulation was higher under N2 and N3 than N1. Compared with CDI and FDI, leaf to fruit ratio reduced but harvest index significantly increased in ADI, while those variables showed no significant difference among diffe-rent N application rates. The ratio of pruning amount to the biomass accumulated in the current year in ADIN2 was the lowest among the treatments. Compared with CDI and FDI, ADI increased grape fruit yield by 6.0% and 10.4%, respectively. Fruit yield was enhanced with increasing nitrogen application rates under the same irrigation condition, with the highest yield under the ADIN2 and ADIN3. Water use efficiency (WUE) increased significantly in ADI compared with CDI and FDI, with the highest value being observed in ADI coupled with N2 or N3. Nitrogen use efficiency (NUE) showed a trend of ADI＞CDI＞FDI. In addition, NUE decreased with increasing nitrogen supply level across the irrigation modes. In conclusion, ADIN2 could reduce the redundant growth of grape tree, promote the transfer of dry matter to fruit, which increased yield and use efficiency of both water and nitrogen, which is a suitable coupling water and nitrogen supply mode for grape production in northern China.

Algal density affects the influences of polyethylene microplastics on the freshwater rotifer Brachionus calyciflorus.

Most previous researches focused on the toxicity of polystyrene microplastics (MPs) to marine organisms, but less on polyethylene MPs and freshwater zooplanktons. The present study aims to elucidate the toxicity of polyethylene (PE) MPs (diameter = 10-22 µm) to the typical freshwater rotifer Brachionus calyciflorus. Firstly, fluorescent microscope observation showed that rotifers could ingest PE MPs and accumulate them in their digestive tracts. Life-table experiments revealed that exposure to 0.5 × 103, 2.5 × 103, and 1.25 × 104 particles/mL PE MPs significantly reduced net reproductive rate and intrinsic rate of pollution increase of rotifers under algal densities (Scenedesmus obliquus) of 0.1 × 106, and 0.5 × 106 cells/mL, but no significant effects were observed under 2.5 × 106 cells/mL algal density. These results showed that PE MPs suppressed the reproduction of rotifer and this negative effect could be alleviated by increasing food supply. The swimming linear speed of rotifers significantly decreased with increasing MP concentrations. The activities of superoxide dismutase and Na+-K+-ATPase significantly decreased in treatments with high concentration of PE MPs under 0.1 × 106 cells/mL algal density, but did not change significantly in MP treatments under 0.5 × 106 and 2.5 × 106 cells/mL, compared to the control. Glutathione peroxidase activity significantly increased in treatments with 1.25 × 104 particles/mL and 2.5 × 103 particles/mL under 0.1 × 106 and 0.5 × 106 cells/mL algal density, respectively, but did not change significantly in all MP treatments under 2.5 × 106 cells/mL. Exposure to PE MPs might lower the gathering capacity of algae, induce oxidative stress, trigger cell membrane damages and disturb energy metabolism in rotifers, which can explain the PE MPs toxicity to rotifer reproduction.