Synthesis Of The PbS Nanoparticle And Its Translocation In Plant

Over the past decade,the production and applications of metal-based and metal-oxide nanoparticles（MBNPs and MONPs,respectively）have increased significantly due to their enhanced physicochemical properties and biological activities when compared with their bulk parent materials.In the past two decades,the uses of engineered nanoparticles（NPs）have been increased significantly.In the process of production,transportation,consuming and abandonment of nanomaterials,some nanoparticles will inevitably enter the ecosystem and the environment.Once these NPs（MBNPs and MONPs）enter agricultural soil via direct or indirect pathways,they can interact with crop plants and thus pose a threat to both animal and human health through food chain pathways.PbS nanomaterials are of great concern because of their potential toxicity and unavoidable releases of multiple commercial applications of nanoparticles（NPs）.Commercial NPs act as mediators of damage to plant cells and pose potential toxicity to plants and human health.Therefore,we synthesized PbS nanoparticles with high purity by chemical synthesis method and taking the plant effect of nanoparticles as the starting point,the present study aims at using the hydroponic experiments to（1）study the effects of PbS NPs on seed germination and seedling growth of Zea mays L.;（2）reveal the toxic effects of PbS NPs on Zea mays L.and the corresponding toxic mechanism;（3）explore the absorption and transportation of PbS NPs within the Zea mays L.body;（4）elucidate the possible pathways of PbS NPs entering the plant and the rules related to PbS NPs distributing and accumulating in the plant and（5）illustrate the law of toxicological effects of nano-PbS on higher plants as well as the principle and mechanism of corresponding toxicological effects.In this study,PbS nanoparticles were synthesized by chemical route.The PbS NPs were characterized with XRD,XPS,SEM,HRTEM,EDS and other technical means,the average physical size of PbS NPs was 16±6 nm,the purity was almost 100%.The effect of PbS NPs on the germination of maize seeds through Zhengdan 958 maize seed germination experiment,the findings indicate that PbS NPs has phytotoxic effects on seeds germination and similar effects in root elongation,all test illustrated that a significant positive influence on seed germination was recorded.However,some differences occurred between all treatments in comparison to the control group.For example,after 6 days the PbS NPs suspension with the levels of 5,10,20,30,40,50 mg/L and Pb2+ reduced the germination rate by 20.33%,1.33%,20.33%,7.67%,10.33%,17.67%,10.33%respectively,comparing to the control group.At the same time,under the experimental conditions,a dual behavior of promoting root elongation at the concentrations of 10 and 30 mg/L PbS NPs and exerting inhibitory effects at other levels was observed.It was noted that the inhibition of the maize root elongation compared to other treatments was recorded at 20 mg/L PbS NPs treatment.The results indicated that with the elevated concentrations of PbS NPs,the plant biomass and root length were significantly reduced,illustrating that increased phytotoxicity of PbS NPs depends on degree of concentration After 15 days of exposure with PbS NPs treatments and Pb2+ions（1.5 mg/L）,the fresh shoot biomass was reduced by 49.11%（5 mg/L PbS NPs）,32.58%（10 mg/L PbS NPs）,62.246%（20 mg/L PbS NPs）,46.23%（30 mg/L PbS NPs）,69.42%（40 mg/L PbS NPs）,56.37%（50 mg/L PbS NPs）,and 62.32%（1.5 mg/L Pb ions）,respectively compared to controls（CK）.This indicated that all PbS NPs treatments,including Pb2+ions group,had significantly reduced maize biomass,but PbS NPs treatments of 20,30,40 mg/L and Pb2+were significantly different than CK.The 5 mg/L,10 mg/L,50 mg/L treatments for dry shoot biomass had no significant differences compared to CK,but 20,30,40 mg/L and Pb2+ ions group had significant differences.For root fresh and dry weight of the maize seedlings,the effects of concentrations of PbS nanoparticle suspension and Pb2+ ions solution were significantly different,and also significantly different when compared to the CK.However,the maize seedlings exposed to lower concentrations,for example,5 mg/L,l0mg/L of PbS NPs could exhibit increased the shoot and root biomass（fresh and dry）compared with other concentrations,except the CK.The uptake and transport of PbS nanoparticles by maize seedlings.Through the experiment of maize seedlings and the determination of total lead content in the roots and above-ground parts of corn,it can be seen that the treatment of different concentrations of PbS nanoparticles makes.The Pb concentration in maize shoots and roots after 15 days exposure to different concentration of PbS NPs（5,10,20,30,40,and 50 mg/L）and 1.5 mg/L of Pb2+ ions.With the increasing of NPs concentration,the contents in plants were also increasing comparison with CK.It was Found that Pb contents in shoots were significant different among all the treatments,also significant different with CK treatment.The Pb concentrations in shoots exposed at the levels of 5,10,20,30,40,and 50 mg/L of PbS NPs were 1.7,1.9,1.8,1.9,1.8,and 2 times higher than the controls respectively,and all above 1.2 times higher than the Pb ions respectively.However,the Pb contents in roots in different treatments of PbS NPs at 5,10,20,30,40,and 50mg/L were 3.4,5.6,6.5,6.3,5.2,and 6.1 times higher than the controls and 2.4,4.0,4.6,4.4,3.6,4.3 times higher than the Pb2+ions treatment,respectively.All treatments were significant difference.Comparison with CK,5 and 20mg/L of PbS NPs had the significant difference.It can be reasonably inferred that PbS NPs have entered the roots of corn seedlings and migrated to the aboveground parts of corn seedlings,which will affect the growth of corn seedlings.For the better understanding the translocation of PbS NPs to maize seedlings,TEM/STEM analysis was performed in the combination with EDS to determine the PbS NPs presence in the roots and shoots.The roots and shoots of the maize seedlings exposed to the treatments of 5 mg/L,10 mg/L,20 mg/L,30 mg/L,40 mg/L,and 50 mg/L of PbS NPs,Pb2+ ions and the controls were analyzed by TEM/STEM.The images indicated the abundant dense dots not only existed inside the cell wall but also existed in intercellular space and cytoplasm of the cortical cell of maize seedlings when exposed to different concentrations of PbS NPs as well Pb2+ ions treatment.However,the PbS dots were not observed in the unexposed controls.The corresponding EDS mapping showed the presence of Pb and S elements in the doted spots,which confirmed that the observed dots were PbS NPs or their aggregations in plant tissues.The observations of PbS NPs in intercellular space demonstrated that the PbS NPs could pass the cortex via apoplastic pathways or through the epidermis to transfer into the plant body.The results illustrate PbS NPs can enter the cell wall and exist in intercellular space and cytoplasm of the cortical cell of maize seedlings by apoplastic and symplastic pathways.This study highlights the importance of the uptake,phytotoxicity,and biotranslocation of PbS NPs in maize crops and demonstrates the possible transfer into human food as an outcome of the fate of PbS NPs in plants.