Effects Of Different Selenium Types On Cadmium Uptake And Transport In Rice

Cadmium pollution is very serious,which is a global environmental problem.Cadmium is a kind of non-essential trace element for plants,which is highly toxic to plants.It pollutes water and soil through industrial and agricultural production,and enters human body through food chain enrichment,which is harmful to human health.Rice is the main food crop in China,which plays an important role in the diet structure of residents.However,rice has a strong ability to accumulate cadmium.Therefore,reducing cadmium pollution and improving rice quality are of great significance to food security and people’s health.Selenium,as a beneficial element,has antagonistic effect with heavy metals.Selenium is a kind of trace element,which is one of the essential nutrients in organism.In this study,rice was used as the experimental plant to study the effects of different types of selenium on the absorption,transportation and accumulation of cadmium in rice through hydroponic and pot experiments,and to explore its mechanism.The purpose of this study was to provide theoretical basis and data support for reducing cadmium content and improving selenium level in rice.The main results are as follows:(1)In order to explore the effects of different types of selenium treatment on the growth of rice,water culture experiment was conducted.The results showed that Cd inhibited the growth of rice roots,stems and leaves,and with the increase of Cd concentration,the greater the inhibition on rice.The addition of exogenous Se significantly alleviated the toxicity of Cd to rice,especially the increase of dry weight of root,stem and leaf,rice and brown rice.Cd stress reduced the average root diameter and total root volume of rice roots.The total root length,total root surface area,average root diameter and total root volume of rice roots treated with Se were larger than those of control,and the parameters gradually increased with the increase of Se concentration.The effects of three different types of Se on root growth,Cd and Se uptake were ISe>Che Se NPs>Phy Se NPs.(2)In order to explore the mechanism of selenium on cadmium transport,differential centrifugation was used to study the effect of selenium on the subcellular distribution of cadmium in various organs of rice.The results showed that the distribution of Cd in subcellular components of roots,stems and leaves was cell wall > soluble > organelle.In Cd0.5 treatment group,when adding the same kind of Se,with the increase of Se concentration,the content of Cd in cell wall decreased,and the content of Cd in organelle and soluble part increased.However,in the Cd1.0 treatment group,when adding the same kind of Se,with the increase of Se concentration,the Cd content in the cell wall increased,and the Cd content in the organelles and soluble parts decreased.Under the same concentration of Cd,the increase of Se concentration has little effect on the content of each component of rice stem and leaf subcellular.(3)In order to study the effect of different treatments on the ultrastructure of rice roots,the results of transmission electron microscopy showed that the control group had abundant organelles,clear membrane,smooth cell wall,and obvious nucleoli and vacuoles.It was observed that the cell wall became thick and unsmooth with many adherents after Cd treatment.After adding Se,the damage of Cd on root system was alleviated,the nucleolus and cell wall were clearly observed,but it was still thicker than the control group.(4)In order to explore the regulatory effect of different types of selenium on cadmium,a pot experiment was conducted in cadmium contaminated soil.Different concentrations of organic selenium(OSe),inorganic selenium(ISe)and physically synthesized nano selenium(Phy Se NPs)(0,0.5,1.0mg/kg)were applied to explore the accumulation of cadmium in rice.The results showed that three different types of Se could promote the growth of rice,and the promotion of Se content in soil was: ISe>Phy Se NPs>OSe,and the inhibition of Cd content in rice roots,stems and roots was: Phy Se NPs>ISe>OSe.