Effects Of Continuous Flooding And Liming Application On Cadmium Accmulation And Its Mechanism

Cadmium?Cd?is a highly toxic heavy metal element,which through the soil-rice food chain system enters into the human body,and causing potential harm to the human body.In China,South Korea,Japan and other rice-based countries,rice is the main source of human intake of Cd.Therefore,it is of great importance to understand the low accumulation and regulation techniques of rice Cd and its mechanism,as well as the safe production of Cd in rice paddy field and the basic theory of Cd accumulation in rice.In this study,two rice cultivars with different Cd accumulation FP36 and ZJZ17 were used as materials.The effects of continuous flooding and lime treatment on the Cd content in these rice cultivars were studied in pot experiment.The results showed that the soil available Cd,plant Cd content,rice root Cd transcription of related key genes were changed under continuous flooding.Effects of water and lime on Cd accumulation in rice and its regulation mechanism.The results were as follows:1.Compared with the control,the results showed that continuous flooding sharply reduced Cd content of FP36 and ZJZ17 under pollution condition at middle tillering stage with the decline of root Cd content were 39.5%and 33.9%while that of shoot Cd were62.1%and 71.7%,respectively.Continuous flooding also significantly reduced Cd content of rice root,shoot and milled rice at mature stage.Upon the management root,shoot and milled rice Cd content of FP36 were identified to be decreased by 36.4%,43.7%and 36.8%while that of the ZJZ17 were 62.5%,61.5%and 55.4%,respectively.Furthermore,the soil available Cd of FP36 and ZJZ17 significantly decreased by 12.1%and 17.7%,and root plaque Cd content by 52.2%and 43.1%under continuous flooding treatment,respectively.While soil available Fe content?23.7%and 10.3%?and Mn content?24.5%and 43.9%?of FP36 and ZJZ17 significantly increased.As well,root plaque Fe?83.1%and 81.5%?and Mn content?41.5%and 27.7%?were also elevated under continuous flooding.Simultaneously,the relative expression of OsNramp1?58.3%and 58.0%?and OsLCD?21.6%and 17.8%?genes were also down-regulated by continuous flooding in rice root.Continuous flooding decrease Cd uptake by decreasing soil available Cd content and down-regulating Cd uptake related genes expression of OsNramp1 and OsLCD in rice.2.With the increase of lime dosage,the contents of Cd in roots,shoots and milled rice of two rice varieties showed a trend of increasing in first time and then decreasing later.When the addition of exogenous Cd was 1.0 mg·kg^-1,the amount of lime increased from 0 g to 1.0g,and the Cd contents of FP36 and ZJZ17 increased in the roots by 36.3%and 5.6%,in shoots by 43.3%and 14.5%,and in milled rice by 8.9%and 16.0%,respectively.When the amount of applied lime increased from 1.0 g to 6.0g,Cd contents of FP36 and ZJZ17decreased in roots by 71.5%and 58.6%in shoots by 69.1%and 59.0%,and in milled rice Cd by 66.8%and 100%,respectively.When the addition of exogenous Cd was 1.5 mg·kg^-1,the amount of lime increased from 0 g to 0.5 g,and Cd contents of FP36 and ZJZ17 in the roots increased by 85.2%and 150%),in shoots by 130%and 150%,and in milled rice by 26.2%and 110%respectively.Finally,when the amount of applied lime increased from 0.5 g to 6.0g,the Cd contents of FP36 and ZJZ17 in the roots showed reduction of 77.2%and 62.9%),in shoots of 69.4%and 61.0%,and in milled rice of 74.2%and 61.6%respectively.However,there was no significant difference in Cd accumulation between the two rice cultivars when adding different amounts of lime in the absence of exogenous Cd at tillering and mature stages.3.The lime treatment regulates the Cd uptake and accumulation by regulating the bioavailability of soil Cd and the expression of Cd ion transporter gene.The results showed that the Cd,Fe,Mn and Zn amount in the DTPA extracts from these two rice varieties decreased following the lime dosage increase?from 0 to 6g?.Subsequently,the relative expression of Os Nramp5 and OsIRT1 genes in the roots of these two rice varieties was significantly proportionally increased with lime dosage increase?from 0 to 6g?.Therefore,under the condition of different levels of lime treatment,the Cd content of rice increased first and then decreased;The effect of reducing Cd content in the soil and the up-regulation of OsIRT1 and OsNramp5 expression were up-regulated in rice root Cd uptake and transduction.In this study,two rice varieties with different Cd accumulation were selected to analyze the effect of continuous flooding and lime on Cd accumulation rice.The regulatory mechanism revealed could provide theoretical guidance for the actual production of rice.