Effect Of Polystyrene Nano-plastics On Germination And Antioxidant Activity Of Rice Seeds

The rapid development of industry,agriculture and urbanization has resulted in a large number of plastics accmulation in soil.Plastics are gradually degraded into microplastics or nanoplastics.Due to the small particle size,nanoplastics are easily taken up by organisms,and may amplify their toxic effects through the migration of the food chain,which is a hot issue in environmental research.However,the current research on the impact of nanoplastics mainly focuses on Marine life and water environment,and there are few researches on land plants.Therefore,in this study,200nm polystyrene nanoplastics(PS-NPs)were used as experimental materials,and rice seeds(Oryza sativa L.,variety:ZH11)was used as the test plant,four concentrations of nano-plastic solution(0 mg·1-1,0.1 mg·1-1,10 mg·1-1,1000 mg·1-1)were set.The effects of different concentrations and different seeding methods(distilled water seeding,nano-plastic seeding)on rice seed germination were studied from four aspects:electron microscope observation,germination index,antioxidant enzyme activity and transcriptional expression.The main findings are as follows:(1)It was found that PS-NPs was entered into rice seeds,roots and buds,and dispersed as single grains or aggregated into clusters and chains.(2)Different concentration of nanometer plastics had no significant effect on the final germination rate,germination potential,bud length,lateral root number,Superoxide Dismutase(SOD)activity and Peroxidase(POD)activity of rice seeds,but had significant promoting effect on root length.Meanwhile,the accumulation level of reactive oxygen species(ROS)in the root system will increase.High concentration(1000mg·L-1)nanoplastic treatment significantly reduced Catalase(CAT)activity in rice buds(p<0.05).(3)There was no significant difference in germination rate,germination vigor,germination index,vigor index,root length,bud length and lateral root number between two different immersion methods(distilled water immersion and NPs immersion)under the same concentration of NPs.However,the high concentration(1000 mg·L-1)treatment significantly prolong the average germination time of seeds.There were also some differences in the activity of antioxidant enzymes in rice buds.High concentration(1000mg·L-1)of nano plastics could significantly reduce SOD activity and increase POD activity.CAT activity was significantly increased at low concentration(0.lmg·L-1)and high concentration(1000mg·L-1)(p<0.05).(4)PS-NPs can induce the up-regulation of genes related to plant roots antioxidant activity,such as the up-regulation of genes involved with the biosynthesis of flavonoids and flavonols,and the down-regulation of genes involved with linolenic acid metabolism and nitrogen metabolism pathways.