The Phytotoxicity Assessment Of Metal Oxide Nanoparticles On Maize(Zea Mays L.)and Rice(Oryza Sativa L.)

The rapid development of nanotechnology bring us huge economic benefits,it also give us potential environmental problems and health risks.With nano materials are widely used,nanotoxicity is receiving increasing attentions currently.As the most widely used nanomaterials,the toxicity studies of metal oxide nanomaterials are receiving considerable attentions.Corn and rice,the most important food crops in the world,with extensive planting area,are vulnerable to the environment pollutants.In this study,the flat germination experiments were conducted to study the effect of seven metal oxide nanomaterials?nCeO₂,nFe₃O₄,nSiO₂,nTiO₂,nAl₂O₃,nZnO,nCuO?on corn and rice.The toxicity effects were analyzed by the seed germination rate and root length,in addition,the factors which could affect the toxicity of nanomaterials were also discussed in this paper;Second,by means of soil culture,the physiological effects of copper oxide nanomatericals on rice seedling were studied;Finally,by means of Histological sections and Real-time PCR,the cellular morphology of corn root cell and expression levels of corn root cell wall related gene?ZmPXPA1,ZmPXPA5,ZmPXPB1,ZmMHA?were tested,hopes to provide some basic theoretical data on toxicity of nanomaterials in physiological,cellular and molecular level.The research results showed that metal oxide nanomaterials didn't affect the germination of corn and rice,but nAl₂O₃,nZnO,nCuO significantly inhibited the root elongation of corn and rice,at the concentration of 2000 mg/L,the root elongation was significantly inhibited by nCuO?95.73% for maize and 97.28% for rice?,nZnO?50.45% for maize and 66.75% for rice?,minor phytotoxicity of nAl₂O₃ was only observed in maize.The phytotoxicity toxicity came from the nanomaterial itself,and related to plant species,exposured concentrations and particles size;the results of Histological sections presented that the root cell swelling and distortion under nCuO stress,we suspected that this might be a defense mechanism of plant to resist the nCuO stress;qRT-PCR results showed that the expression of ZmPXPA1,ZmPXPA5 decreased significantly and the expression of ZmMHA increased significantly,no altered expression of ZmPXPB1 were detected,which presented that the copper oxide nanomaterials could influence the expression of cell wall related gene of maize,finally affected the morphology of cell wall and root elongation;Copper oxidenanomaterialscouldalsobreakthebalanceofreactiveoxygenspeciesmetabolism,destroytheintegrityofthecellmembranestructure,loweredthecontentofchlorophyll,andeventuallyleadtothedecreasedofricebiomass.