The Study On Effect Of Titanium Dioxide Nanoparticles On Seeds Germination And Seedling Growth Of Mulberry

Titanium dioxide nanoparticles（TiO₂ NPs）are among the most widely used inorganic nanomaterials in industry,environmental governance,medicine and food additives.With the increase of TiO₂ NPs,the content of TiO₂ NPs in soil and water also keeps rising.There are increasing concerns regarding their potential risks to the environment and plants.However,the effect of high concentrations of TiO₂ NPs on mulberry（Morus alba L.）and its mechanism remain unclear.Therefore,this study systematically evaluated the effects of TiO₂ NPs on the growth and physiology of mulberry from the aspects of morphology,physiology,histopathology,transcriptomics and metabolomics.The main results are as follows:1.Absorption and transport of TiO₂ NPs in mulberry seedlingsIn this study,we found that TiO₂ NPs could be absorbed by the roots of mulberry seedlings and transferred to the stems and leaves of the plants,and TiO₂ NPs would continuously accumulate in the mulberry seedlings.In the underground part of the mulberry seedling,the content of TiO₂ NPs in the mulberry seedling increased with the increase of the use concentration,and the accumulation amount was about 5 times the amount of TiO₂ NPs.In addition,TiO₂ NPs also affected the absorption and accumulation of metal elements,and changed the steady-state of Fe,Mn,Cu and Zn elements in the mulberry seedlings.2.Effects of TiO₂ NPs on the growth and development of mulberry seedlingsThe germination of mulberry seeds was significantly inhibited by different concentrations（100,200,400 and 800 mg/L）of TiO₂ NPs treatment.The results of pathological sections and transmission electron microscopy showed that the root and leaf tissues of mulberry seedlings were characterized by fragmentation and vacuolation,and the number and size of chloroplasts were decreased.In addition,the homeostasis of metal ions was also disrupted.At the same time,TiO₂ NPs affected the content of malondialdehyde,catalase,proline,and soluble proteins related to stress resistance of mulberry seedlings.These results showed that TiO₂NPs was not conducive to the germination and growth of mulberry seeds.3.Transcriptome and metabolomics analysis of mulberry seedlings treated with TiO₂ NPsBased on the transcriptomic data,it is clear that TiO₂ NPs treatment mainly affected the expression of genes related to energy synthesis and transport,protein metabolism,and response to stress.Meanwhile,the results of metabolomics showed that 42 metabolites produced significant differences after TiO₂ NPs treatment in mulberry,of which 26 differential metabolites were up-regulated in expression and 16 differential metabolites were down-regulated,mainly including metabolic pathways such as secondary metabolite biosynthesis,citric acid cycle,and tricarboxylic acid cycle and other metabolic pathways,and the presence of isocherry glycosides was found for the first time in mulberry and its response to TiO₂ NPs.According to transcriptomic and metabolomic association analysis,most of the differentially transcribed genes have strong correlation with differentially metabolites.In summary,TiO₂ NPs can be absorbed and accumulated by the roots of mulberry seedlings,which in turn affects the morphogenesis of mulberry seedling roots,causes plant peroxidation damage,reduces stress resistance of mulberry trees,leads to photosynthesis obstruction,and damages leaf tissue integrity.The results of this study enrich the understanding of the effects of TiO₂ NPs on plants,and provide a reference for a comprehensive scientific assessment of the potential risks of nanomaterials to the ecological environment.