The Response Of Rice To Organoarsenics Stress And Regulation Mechanisms By Silicon

It is especially important to guarantee rice safety for rice plant is one of the most important food crops and more than 50%people in the world live on rice,including China etc.At present,the arsenic(As)contamination in rice is a vital quality safety problem.Because of the significant differences of As toxicities among different As speciations,to evaluate the safety of As in rice,not only the total and inorganic As contents,but also the speciations and contents of organoarsenics speicies should be taken into consideration.Even though more and more researches have been focused on the absorption,transportation,accumulation and regulation of As in rice plant in recent years and some achievements have been obtained.However,most of the studies focused on the stress of inorganic As on rice and total As content in rice during a certain growth period.Few studies from domestic and overseas focused on the growth,absorption,metabolism and control measures of rice under the stress of organoarsenics speciations.Organoarsenics species,such as arsanilic acid(ASA)and monomethylated arsenic(MMA),were once extensively used in agriculture and are still widely used in industry now.In this paper,in order to provide the basis for reducing the absorption of organic As by rice,the influences of different organoarsenics with different concentrations on the whole growth process of rice(Oryza sativa L.)were analyzed by using water and soil culture methods,and the physiological mechanism of silicon(Si)alleviating the toxicity of organic As stress to rice was discussed by determinating physiological indexes in rice under different organic As stress.The results were as follows:1.Method establishment for the simultaneous determination of five As species(As(III),As(V),DMA,MMA and ASA)in rice tissues and rice grains by high performance liquid chromatographyinductively coupled plasmamass spectrometry(HPLC-ICP-MS).In this method,the calibration curves for five species was linear of 0~12.5 mg/L,and all correlation coefficients(R~2)were larger than 0.9995.The detection limits were 0.15?g/L~0.36?g/L and the quantitation limits were 0.50?g/L~1.20?g/L for five As speicies.The average recovery rate was between 84.8%and 105.6%,and relative standard deviation was 0.7%~4.2%.2.The differerence of organoarsenics–resistant among five south typical rice varieties.Through the pot experiment,five south typical rice varieties,namely,tianyou116,guangyou 116,tianfeng B,yuejinsimiao 2 and black rice were planted,and the characteristics of absorbing and accumulating 100 mg/kg(to numbered as As)ASA and MMA in mature period were compared.Results showed that As(?),As(V),MMA,DMA and ASA were detected in ASA treated rice,and the kinds and contents of these As speices in rice were related to rice varieties.As contents in roots were the highest.As(?)was accumulated in roots,stems,leaves,ears and grains of each rice cultivar.Hybrid rice tianyou 116 had the highest total As content,followed by conventional rice yuejinsimiao2,while glutinous rice black rice had the lowest As content.MMA,DMA,As(?)and As(V)were detected in MMA treated rice.The contents of all kinds of As species in rice tissues from large to small were roots,leaves,stems and ears.MMA,As(?)and DMA were only accumulated in ears of rice tianyou 116 and guangyou 116,while other rice varieties were sterility.Tianyou 116 had the highest total As content,followed by guangyou 116,tianfeng B and yuejinsimiao 2,while black rice had the lowest total As content.Thus,the As tolerance of hybrid rice tianyou 116 was better than that of conventional rice studied.The best As resistance of the conventional rice among four studied rice varieties was yuejinsimiao 2.Therefore,rice tianyou 116 and yuejinsimiao 2were selected as the As-tolerant variety of hybrid rice and conventional rice,respectively.3.The effects of different organoarsenics on rice seed germination.Three south typical rice varieties,namely,black rice,tianyou 116 and yuejinsimiao 2,were selected as the experimental materials.Water culture experiments were carried out on germination of rice seeds under five concentrations of ASA and MMA.Results showed that the germination,coleoptile length,root length,fresh and dry weights of rice seedlings were significantly inhibited under the effect of high concentrations of ASA and MMA,and inhibition increased with the increasing organoarsenics concentrations.At the concentration of 25 mg/L,two organoarsenics species showed different effects on different rice seed varieties.Thus,organoarsenics species still had toxic effects on rice seeds germination at high concentrations even if they were less toxic.4.The dynamic characteristics of absorption and accumulation of different organoarsenics by different rice cultivars at different growth stages.Through pot experiment,the dynamic characteristic differences of absorption and accumulation of organoarsenics in rice tianyou 116 and yuejinsimiao 2 were investigated at different growth stages(tillering stage,filling stage and mature stage)at five spiked concentrations of ASA and MMA,respectively.Results showed that for ASA treatments,As(?),As(V)and ASA were detected in roots,stems and leaves of two rice cultivars(except for youjinsimiao 2 leaves)at tillering stage and their contents from large to small were ASA,As(?)and As(V).As(?),As(V),DMA,MMA and ASA were detected in rice tissues at filling stage and mature stage.ASA content was highest in filling stage,but As(V)content was highest in mature stage.As(?),DMA and MMA were detected in grains,and the contents of DMA and MMA were higher than As(?)content.For MMA treatment,As(?),DMA,MMA and As(V)were detected in rice tissues at three growth stages.MMA content was higher than other As species at the same spiked concentration.In general,as the spiked MMA concentrations increased,the contents of four As species increased.The male killing effect of MMA made only rice tianyou 116 produced grain at MMA spiked concentration of 50 mg/kg.As(?)and DMA were detected in tianyou 116grains,and the contents of DMA were higher than the contents of As(?).From the above,it could be seen that the organoarsenics absorbed by rice roots were gradually transferred to the rice overground,then transformed into other As species and accumulated in overground tissues with rice growth.ASA was mainly tranfered to As(V),and MMA was still in main ratio.This might be related to different metabolic pathways of ASA and MMA by rice.5.The study of the antioxidant system response of rice to organoarsenics stress.Hydroponic experiments were carried out to investigate the antioxidant response characteristics of black rice,tianyou 116 and yuejinsimiao 2 at seedling stage at physiological level.Results showed that ASA with the concentration of 50 mg/L could improve the shoots growth of black rice and tianyou 116.When ASA treated concentrations increased,the growth of shoots and roots of three rice cultivars was inhibited,the contents of malondialdehyde(MDA)and the total arsenic were increased,the activities of antioxidase superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD),the contents of antioxidant glutathione(GSH)in the shoots and roots of black rice and tianyou 116,and the contents of soluble protein in shoots and roots of three rice cultivars were increased first and then decreased.The contents of ascorbic acid(AsA)and soluble protein in roots of black rice and tianyou 116,the activities of SOD,CAT and POD,the contents of GSH,AsA and soluble protein in shoots and roots of yuejinsimiao 2were all decreased.MMA with the concentration of 50 mg/L could improve the roots growth of black rice.When MMA treated concentrations increased,the growth of shoots and roots of three rice cultivars was inhibited,the contents of MDA and total As were increased,the activity of CAT in shoots of black rice,the activities of SOD,CAT and POD,the content of GSH and AsA in the roots of black rice,and the contents of soluble protein in shoots and roots of three rice cultivars were increased first and then decreased.The activities of SOD and POD,the contents of GSH and AsA in shoots of three rice cultivars,the activities of SOD and CAT and the contents of GSH and AsA in roots of yuejinsimiao 2 and tianyou 116 were all decreased.Results indicated that the antioxidant system responses of rice to different organoarsenics stress were different.Under weak stress,rice could resist the organoarsenics stress damage by improving the antioxidant system,showing strong self-regulation ability and anti-arsenic stress ability.While the antioxidant system of rice was damaged and the antioxidant capacity of rice decreased under heavy stress.The stress tolerance of rice to organoarsenics depended on varieties and tissues of rice,species and concentrations of organoarsenics,etc.6.The physiological response mechanism of Si-alleviated organoarsenics stress of rice seedlings.The physiological effect mechanisms of Si application on rice black rice,youjinsimiao and tianyou 116 under ASA and MMA stress were investigated by rice seedling hydroponic experiment.Results showed that both ASA and MMA at the concentration of 100 mg/L(numbered as As)put stress on rice.When Si was added into the ASA(MMA)treatments,it could reduce lipid peroxidation,raise the activities of SOD,POD and CAT,increase the contents of GSH,AsA and soluble protein,reduce the absorption of ASA(MMA)of rice seedlings and improve the growths of rice,making the resistance of rice seedlings enhanced.The results of this study provided the theoretical basis for applying Si fertilizer to alleviate the stress of organoarsenics and reduce the absorption of organoarsenics in rice.