Study On The Regulation Effect Of Silicon On Cadmium Accumulation In Rice And Its Mechanism

The accumulation and migration of cadmium in the soil results in the deterioration of soil quality,which seriously affects the material circulation in the soil circle,and then enters the human body through the food chain through the absorption of crops,thus endangering human health.The content of silicon(Si)in the earth’s crust ranks the second,and the content in nature is very rich.In this study,sodium silicate of jiushui was used as the silicon source,in an attempt to find a feasible and effective method of applying silicon fertilizer,and to study the mechanism of the effect of silicon on cadmium accumulation in rice.The pot experiment was used to compare the growth and heavy metal accumulation of two varieties of rice under two different soils and the effects of different exogenous addition of sodium silicate of nine water.The two varieties are NF18(CNS early 17,ZJ17,cadmium low-level tired variety)and NF30(radial rice varieties is tasted,FP36,cadmium accumulation of high variety),the two types of Soil are taken from xiangyin county of hunan province Soil(Soil A)and fuyang district,hangzhou city,zhejiang province Soil(Soil B),silicon source gradient is set to CK,3 g,6 g/B three gradient,in basal one-time join,rice potted plant experiments.The results showed that soil application of 3g/BBL silicon fertilizer increased the content of Fe and Mn in the extracted state of DTPA in the two soils,which was competitive with the available state cadmium in the soil,and thus reduced the absorption of cadmium by rice.In the two soils,soil application of 3g/BBL silicon fertilizer was more effective than soil application of 6g/BBL silicon fertilizer.Soil application of 3g silicon fertilizer increased the above-ground biomass of rice.In the two soils,silicon has two effects on promoting and hindering the transfer of cadmium from the soil to the overground of rice.When the application amount is 3g/BBL,it hinders the transfer of cadmium to the overground and the application amount is 6g/BBL to promote the transfer of cadmium from the soil to the overground of rice.With the increase of the dosage of silicon,the cadmium content in overground,root and brown rice decreased first and then increased.In the tillering stage,the cadmium content in overground,root and brown rice decreased by 26.4%and 52.6%,respectively,in the tillering stage,when NF18 was cultivated in soil,compared with that in the tillering stage without soil fertilization.With Soil B as the cultivation Soil,it decreased by 22.1%and 37%,respectively.Soil A as the root of NF30 decreased by 5.8%and 29.9%.Fuyang soil dropped by 2%and 14%,respectively.At the completion stage,the cadmium contents in brown rice,overground and root systems of NF18 planted on Soil A decreased by 40.2%,68%and 41.3%,respectively,compared with those without Soil fertilization.Soil B was used as the cultivation Soil,which decreased by 28%,24.3%and 58.7%respectively.NF30 with Soil A as its root system decreased by 19%and 36%,respectively.The brown rice,the overground part and the root system of the cultivated Soil B decreased by 29.1%,37.7%and 61%,respectively.When the dosage of silicon fertilizer was doubled,namely,6g/barrel of silicon fertilizer was applied to the soil,the transfer of cadmium in the soil was promoted by rice,with no significant difference or significant improvement compared with the control group.In the tillering stage,there was no significant difference in the cadmium content in the overground part and root system of the two cultivars.At the completion stage,the cadmium content in brown rice,overground and root increased by 27%,43.2%and 73%,respectively,in NF18 cultivated in Soil A.Soil B was cultivated,14.8%,13%and 25%.NF30 using Soil A as the cultivation Soil,the content of cadmium in brown rice and overground increased significantly by 32%and 26.7%respectively.There was no significant difference in the content of cadmium in brown rice,overground and root of NF30 cultivated in Soil B.According to the comprehensive soil and varieties,the effect of soil application of 3g/BBL(45kg/mu)of silicon fertilizer is attributed to the application of 6g/BBL(90kg/mu)of silicon fertilizer.This study also determined the effect of soil siliconization on the relative expression of Cd related genes in two soils of two rice varieties.In Soil A,the expression of OsNranmpl gene was inhibited by the application of 3g/BBL silicon fertilizer.Although the expression of OsNramp5,OsHMA2 and OsHMA3 genes had no significant effect,the expression of these genes was significantly upregulated by the application of 6g/BBL silicon fertilizer.In Soil B,Soil application of 3g/BBL silicon fertilizer treatment,OsNrampl,OsNramp5,OsHMA2 and OsHMA3 gene table were inhibited,but Soil application of 6g/BBL silicon fertilizer treatment had an upregulated trend or no significant effect on the relative expression of the above genes.This indicates that the addition of exogenous silicon fertilizer can significantly improve the Fe and Mn content of soil to compete with cadmium in soil,thereby reducing the absorption of cadmium by rice,and reduce the toxic effect of cadmium on rice by regulating the expression of genes related to cadmium accumulation and transport in rice.The effects of exogenous addition of Na2SiO4·9H2O(10 M,1mM)10 on the vegetative growth of rice seedlings under 5 M cadmium stress for 7 days and 14 days,the expression of related genes after 7 days of treatment,and the antioxidant enzyme activity system after 7 days of treatment were studied by hydroponic experiment.The results showed that adding 1mM Na2SiO4·9H2O could improve the nutrient imbalance of rice caused by cadmium stress and improve the growth of rice,so that the biomass of NF18 and NF30 varieties increased by 21%and 26.8%at 7 days of treatment,and by 27%and 15%at 14 days of treatment,respectively.The plant height of the two varieties increased by 10%and 15%at 7 days and 5%and 13%at 14 days respectively.The root length of the two cultivars increased by 15%and 11%at 7 days,and there was no significant difference at 14 days.The addition of 1mM Na2SiO4·9H2O in foreign aid reduced the cadmium absorption of rice seedlings,and the cadmium content of NF18 in the abovemend and root decreased by 45%and 24.4%respectively at 7 days.The overground and root systems of NF18 were reduced by 39.7%and 31.3%,respectively,after 14 days of treatment.Cadmium content in the overground and root parts of NF30 decreased by 26%and 41%,respectively,after 7 days of treatment.The overground and root systems of NF30 were reduced by 32.4%and 21.8%,respectively,after 14 days of treatment.Exogenous addition of Na2SiO4·9H2O significantly reduced the degree of membrane peroxidation induced by cadmium stress(P<0.05),and malondialdehyde(MDA)content significantly decreased with the increase of treatment concentration.External addition of Na2SiO4·9H2O activated catalase(CAT)in leaves and roots of the two varieties of rice subjected to cadmium stress after 7 days of treatment,and the CAT activity of leaves was higher than that of roots.Exogenous addition of Na2SiO4·9H2O also increased the activity of peroxidase(POD),and its active roots were higher than its leaves.Exogenous addition of Na2SiO4·9H2O also significantly increased the activity of superoxide dismutase(SOD),which was enhanced with the increase of the concentration of added silica,and the SOD activity of leaves was higher than that of roots.The addition of Na2SiO4·9H2O significantly increased the soluble protein content of cadmium-stressed rice leaves and roots after 7 days of treatment,and the soluble protein content of leaves was higher than that of roots.This indicated that Na2SiO4·9H2O increased the antioxidant capacity of rice seedlings.More importantly,exogenous addition of sodium silicate(Na2SiO4·9H2O)down-regulated the relative expression levels of two rice varieties’ root OsNrampl(61.3%and 77.8%),OsNramp5(85.4%and 74.3%),OsHMA2(71.8%and 80.3%)and OsHMA3(88.9%and 86.4%).