Biological Effect,Uptake And Transportation Of Nano ZnO In Rice(Oryza Sativa L.)

With the rapid development of nanotechnology,the application of nanomaterials is becoming more and more widely.Therefore,nanomaterials will inevitably enter the environment,which has attracted much attention on their safety on both biology and environment.Due to their unique physical and chemical properties,ZnO nanoparticles(ZnO NPs)show a broad application prospect in many areas,such as ceramics,chemical industry,cosmetics,textile,etc.Therefore,more and more people focused on exploring the ecological toxicity and environmental risks of ZnO NPs.However,the research on the molecular mechanism of ZnO NPs on plants is limited and not deep enough,though many researchers reported the phytotoxicity of ZnO NPs.In addition,the effect of ZnO NPs on rice,which is the important food crops,remains unknown.In this study,rice(Oryza sativa spp.japonica)seedlings were used to investigate the effect of ZnO NPs on their development under hydroponic condition,whose concentrations were 25,50 and 100 mg/L,respectively.The results showed that ZnO NPs could inhibit the growth of rice seedlings by reducing their biomass and chlorophyll content.Meanwhile,the inhibiting effect of ZnO NPs on rice enhanced with the increase of their concentrations.Comparing the toxicity of different sizes of ZnO nanoparticles(50 nm,100 nm)and ZnO microparticles(5 μm)on rice,it finds that the toxicity of three sized of ZnO particles was 50nm> 100 nm> 5 μm.In addition,physiological index was determined,which involves the chlorophyll content and carotenoid content,and the expression level of photosynthetic pigment related gene was analyzed.It was found that ZnO NPs could inhibit the expression of the genes responsible for magnesium ions chelating during the process of the chlorophyll synthesis,thus reducing chlorophyll content.By analyzing the activity of antioxidant enzyme and their related gene expression level,we found that ZnO NPs could induce the oxidative damage of rice and reduce the activity of catalase(CAT)and ascorbate peroxidase(APOX).Meanwhile,ZnO NPs could induce the up-regulated expression of superoxide dismutase(SOD)gene to resist oxidative stress.By means of inductively coupled plasma atomic emission spectrometer(ICP-AES),ultra-thin slicing and transmission electron microscopy(TEM),the absorption and transport of ZnO NPs in rice was explored.The results showed that rice could uptake ZnO NPs from the roots,and transport upwards.Using vibration slicing to observe the root cell morphology of rice,the results indicated that ZnO NPs could induce the morphologic changes of cortex cells by shortening their radial length and widening their horizontal length,which made cell morphology change from approximate neat rectangle into irregular oval.