| Microplastics(plastics<5 mm,including<100 nm nanoplastics)have received great attention as a new type of pollutant in recent years,mainly due to the degradation of large plastic waste or direct environmental emissions.Although many studies report on the impact on marine life,their potential impact on terrestrial ecosystems remains largely unknown.Since most of the microplastics that come into the ocean come from land,researchers are beginning to pay more and more attention to the fate and transportation of nanoplastics in terrestrial environments,especially agricultural soils.However,there is currently no direct evidence of the internalization and transport of nanoplastics in terrestrial plants.Terrestrial plants,as a major component of terrestrial primary productivity,play a crucial role in controlling the structure of the food chain and the stability of terrestrial ecosystems and the entire ecosystem.In this study,Arabidopsis thaliala was used as a test organism to systematically study the phytotoxic effects,absorption patterns and distribution of different charged polystyrene nanoplastics(PS-NH2,PS-SO3H)on Arabidopsis thaliana.law.The main research results are summarized as follows:(1)With the increase of the concentration of polystyrene nanoplastics(PS-NPs),the growth of Arabidopsis plants was inhibited.After exposure to different concentrations of PS-NPs(0.3 g/kg,1.0 g/kg)for 7 weeks,the plant height,fresh weight and chlorophyll content of Arabidopsis thaliana in the soil system were inhibited to varying degrees.In the solid medium system,the main root elongation of Arabidopsis thaliana seedlings was significantly inhibited after exposure to different concentrations of PS-NPs(10,50,100 μg/ml)for 10 days.The inhibition level of Arabidopsis depends on the charge and concentration of PS-NPs,and the positively charged PS-NPs have more toxic effects on Arabidopsis.(2)Through differential gene expression analysis and GO function cluster analysis of transcriptomics,positively charged PS-NPs can induce more differential gene expression,which mainly involves pigment biosynthesis and metabolic processes,and water response,ROS response,temperature regulation,and expression of related genes such as circadian rhythm.For PS-SO3H,it mainly involves the expression of related substances such as terpenoids,chemically toxic substances and water-deficient responses.By screening the genes in the transcriptome data,it was found that PS-NH2 can induce more antioxidant activity and down-regulation of genes associated with plant-pathogen interaction.The detection of H2O2 and O2-levels in roots by staining showed no significant change in O2-level under PS-NPs treatment;while PS-NH2 treatment induced more accumulation of H2O2 in roots.(3)Through the morphological analysis of root tissue,it was found that PS-NPs can shorten the cell length of meristematic and mature regions,which is consistent with the accumulation of ROS in the roots.This inhibition effect is more pronounced for PS-NH2 treatment.(4)The distribution of PS-NPs with different charges in plant roots was significantly different by confocal microscopy.Significant internalization was observed for negatively charged PS-NPs and was absorbed near the xylem and the stele.For the positively charged PS-NPs,relatively less fluorescence was observed in the root tissue,and the fluorescence was mostly distributed on the root surface and root hair,which also suggested that PS-NPs could be absorbed by the root hairs in the mature region and internalized near the stele through the apoplastic pathway(5)Analysis of organic acids in root exudates by HPLC revealed that PS-NPs can promote the secretion of more oxalic acid in roots,especially PS-NH2.Our findings directly demonstrate the absorption of nanoplastics by plants and,from a broader perspective,provide a deeper understanding of the ecological effects of microplastics or nanoplastics in the terrestrial environment,agricultural sustainability and human health. |
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