Effect Of Foliar Application Of Polyols On Preventing And Controlling Cadmium Pollution In Rice And Its Mechanism

In China,the soil contaminated with heavy metal is over 16.1% and the target rate of cadmium in the soil is 7%,which rank the first in the soil heavy metal pollution.Cadmium,a non-essential element that is easily absorbed by crops,has a strong migration ability in the soil.Rice is the main grain crops in China and nearly 65% of the national live on rice,while 70% of our rice is exposed to the risk of exposure to Cd,according to the estimates recommended by the USEPA.Therefore,it is urgent to prevent and control pollution of cadmium for China government.In this study,through the rice pot experiment,field test,we aim to study the effect of polyols on the absorption of cadmium in rice.Through the indoor rice seedling cultivation,we explore the effect of spraying polyols effect on rice seedling physiological indexes,antioxidant enzyme activity,manganese,zinc and cadmium distribution in leaf in subcellular level.The effects of polyols on the prevention and control of cadmium pollution in rice were studied,providing new method and scientific basis for prevention and control heavy metal pollution.The main research results are as follows:The results of pot experiment on early rice showed that the application of polyols at two different levels of cadmium pollution could reduce the content of cadmium in rice.The application of polyols in high cadmium pollution soil(total cadmium 3.4mg /kg)could significantly reduce the content of cadmium in rice,and the content of cadmium in rice husk and rice stalk decreased,but most of the differences were not significant.Comparison results of spraying effects in different growth stages of rice showed that the best effect was achieved by spraying polyols in the filling stage alone,and the cadmium content in rice decreased by 73.6%.Secondly,compared with CK,the cadmium content in rice was reduced by 61.8% in the booting stage and filling stage.Spraying treatment at tillering stage,booting stage and filling stage had the worst effect on preventing cadmium accumulation in rice(decreased by 45.1%),but there was no significant difference among the three treatments.The results of pot experiment on second rice(Zengcheng simiao rice)showed that the effect of spraying polyols on cadmium accumulation in rice,resulting in cadmium in rice decreased by 17.27～30.83%,was not as good as that of early rice.Twenty-four hours after the application of the barrier agent,in the test of rice irrigating by heavy rain,heavy rain could affect the barrier effect of the spraying of polyols during the filling period,while the barrier effect of polyol used in the booting stage and grouting stage was not affected when the rice was washed by heavy rain after spraying for 24 hours.Field test results of early rice in Shao Guan showed that the content of cadmium in rice could be reduced by spraying polyols once in rice filling period in three different soil cadmium content areas,decreasing by 33.7～46.7%.With the increase of soil cadmium content,the decrease of cadmium in rice increased.The content of cadmium in rice straw and rice husk decreased with the application of polyol,but the effect on the accumulation of Pb and Zn in rice was not consistent.The field test results of late rice in Qing Yuan showed that the content of cadmium in rice was significantly decreased by 41.7% and 46.6% respectively in the rice filling stage or filling stage and the booting stage.Cadmium content in rice straw and rice husk was significantly reduced after spraying polyol.Under different cadmium stress,the spraying of polyols can reduce MDA content in leaves and increase the content of chlorophyll,proline,protein.However,under the stress of different cadmium,the spraying effect of exogenous polyols is different.Under the stress of low cadmium concentration,polyols can reduce POD and increase the activity of catalase(CAT)and ascorbate peroxidase(APX).Under high concentration of cadmium stress,the POD activity was increased and the activity of CAT and APX was decreased.Results of subcellular level distribution of Cd,Mn and Zn in seedling leaves showed that contents of Cd,Mn and Zn in leaf organelles were in line with F1(cell wall)>F5(ribosome and soluble matter)>F2(chloroplast)>F3(cell nucleus)>F4(mitochondria).The content of cadmium in chloroplast decreased by 23.6% and 21.3%,respectively under different cadmium stress.In high concentration cadmium stress treatment,the content of Cd in F5 increased from 20.85% to 26.2%.The effect of polyols on the distribution of manganese in subcellular structure was similar to that of cadmium.Studies on the cell ultrastructure of seedling leaves showed that the spraying of polyols could maintain the cell integrity and reduce the plasmolysis.In addition,it helps to maintain the integrity of chloroplast morphology and protect the lamellar structure of chloroplast.These results provide a scientific basis for revealing that exogenous polyols inhibit the accumulation of cadmium in rice,and technical support for the prevention and control of cadmium pollution in rice,ensuring food safety.