| Rice(Oryza Sativa L.)is one of the important food crops in China and even Asia.Because of its flooding cultivation method and its unique physiological characteristics,rice is easier to absorb arsenic(As)than other crops.As pollution in rice has caused widespread concern.Therefore,it is very important to study how to reduce the As content in rice for the safe production of As-contaminated farmland rice.In recent years,zinc oxide nanoparticles(ZnO NPs)have been widely used in agriculture-related fields.Studies have shown that ZnO NPs have adsorption capacity for As.The application of ZnO NPs can effectively alleviate the toxic effects of heavy metals on plants and can increase the Zn content in plants.In this paper,through seed germination experiment,nutrient solution cultivation experiment,soil pot experiment,the effects of ZnO NPs on rice growth,physiological metabolism and rice absorption of As and Zn were systematically studied.To explore the effect of exogenous addition of ZnO NPs on the absorption of As and Zn in rice and the mechanism of mitigating the toxicity of As in rice.It aims to reduce the As content of rice grains and provide a reference and scientific basis for the safe production of rice in As-contaminated areas.The main findings are as follows:(1)The seed germination experiment was used to study the stress effect of ZnO NPs in relieving As in rice seed germination.Rice seeds were treated with different concentrations(10,20,50,100,and 200 mg/L)of ZnO NPs and As(0 and 2 mg/L)in petri dishes for 12 days.Under 2 mg/L As treatment,through a series of germination rate,seedling length,seedling dry weight,chlorophyll content,superoxide dismutase(SOD),catalase(CAT)and malondialdehyde(MDA)content Indicators to conduct research.The results showed that under 2 mg/L As treatment,the germination rate increased by 2.3%-8.9% after the addition of 10-100 mg/L ZnO NPs,the weight of the aerial parts increased by 18.2%-42.4%,and the root weight increased by 5.2%-23.9 %,and the chlorophyll content also increased by 3.5%-40.1%.The activities of SOD and CAT were increased by 2.2%-22.8%,7.2%-60.7%,and the content of MDA was reduced by 17.5%-30.8%.In addition,the addition of ZnO NPs at a concentration of 10-200 mg/L can significantly reduce the concentration of As in roots(8.4%-72.3%)and leaves(10.2%-56.6%),and increase the Zn concentration in rice.Overall,10-100 mg/L ZnO NPs can reduce the toxicity of As by increasing germination,biomass,Zn nutrients in rice and by reducing the absorption of As in rice.However,200mg/L ZnO NPs treatment had no significant effect on rice seed germination under As stress.(2)Germination experiments showed that 200 mg/L ZnO NPs had no significant effect on rice seedling length,chlorophyll,and antioxidant enzymes.Therefore,the concentration of ZnO NPs in hydroponic experiments was 10-100 mg/L.Rice seedlings were treated with different levels of ZnO NPs and As(0 and 2 mg/L)for seven days.The results showed that 2 mg/L of As treatment represented a stress condition,which was evidenced by phenotypic images,seedling dry weight,chlorophyll,and antioxidant enzyme activity of rice shoot.The addition of ZnO NPs(10-100 mg/L)enhanced the growth and photosynthesis of rice seedlings.As concentrations in the shoots and roots were decreased by a maximum of 40.7% and 31.6% compared to the control,respectively.Arsenite [As(III)] was the main species in both roots(98.5%-99.5%)and shoots(95.0%-99.6%)when exposed to different treatments.Phytochelatins(PC)content up-regulated in the roots induced more As(III)-PC complexed and reduced As(III)mobility for transport to shoots by ZnO NPs addition.The results confirmed that ZnO NPs could improve plant growth and decrease As accumulation in rice shoots.(3)According to the results of seed germination experiment and nutrient solution culture experiment,rice plants were experimented with As-contaminated soil to study the effects of different concentrations of ZnO NPs on As absorption by rice and the effects of As in soil.The results showed that,compared with the control,ZnO NPs treatment could increase the rice biomass and chlorophyll content of seedlings under As stress,but had little effect on the root of rice leaves in the mature stage,low concentration of ZnO NPs(10 mg/kg and 20 mg/kg)has no significant effect on grain yield,and the application of high concentrations of ZnO NPs(50 mg/kg and 100 mg/kg)reduced the grain yield by 11.18%-12.19%.On the other hand,high concentrations of ZnO NPs(100 mg/kg)can significantly reduce As absorption in rice roots and As concentration in rice grains,but no significant increase in Zn content in grains.Through soil morphological analysis,it was found that the addition of ZnO NPs would reduce soil Eh.Under the action of soil minerals and soil microorganisms,arsenic sulfide precipitates will be formed,which reduces the percentage of effective arsenic,and increases the percentage of residual arsenic,thereby reducing the accumulation of As in rice.The results of this study will allow us to further understand the effect of nanoparticles on the environmental behavior of As in agricultural soils. |
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