The Promoting Effect And Influence Mechanism Of Exogenous Se On The Phytoremediation Technology By Ramie

With the development of human civilization,we are subject to the threat and poisoning of heavy metal pollution.The source of heavy metal pollution usually come from emissions of development of mining,metallurgical industry,chemical industry,steel industry,traffic emissions al et.According to incomplete statistics,there were 26.67 million hectares of arable land has been polluted,of which 10 million hectares of arable land polluted by industrial,10 million hectares of land contaminated by fertilizer pollution and pesticide residues.There were about 20 million hectares of land polluted by the heavy metal pollution,accounting for 20%of the land in the area,including cadmium contaminated land area of about 11.33 million hectares,involving cadmium of 25 regions,11 provinces.Heavy metal pollution control has become essential.Compared with the traditional physics,chemistry engineering repair technical methods,phytoremediation of heavy metal pollution is simple,low investment and operation costs,and no secondary pollution,with potential economic value,etc.while phytoremediation can improve the quality of farmland,improve the lives of residents of the surrounding environment,which is a sustainable,ecological and social benefits significantly repair techniques.This paper studied the effects of cadmium on several physiological indices of different types of ramie,discussed the mechanism of patience and tolerance from Cd stress on different root ramie.And,we also studied and discussed the mechanism of exogenous selenium alleviates cadmium induced toxicity in Bechmeria nivea(L.)Gaud.(Ramie),which studied by antioxidant enzyme systems and DNA methylation levels.The main conclusions of this study are:1)At Lower concentrations(3mg L-1)of Cd stress,there was little effect to the growth to ramie,but when cadmium concentration ? 3mg L-1,the growth of three types of ramie were induced with the increasing of Cd cadmium concentration.At 9mg L-1 Cd stress,ramie,which with the deep root,shown the bigger growth than others,and three types of ramie were increased by 51%,46%,18%,respectively.The result shown that when high concentrations of cadmium after a certain value,there will result in failure of the anti-stress mechanism,resulting in damage to cell membranes and other physical structures.2)The absorption of cadmium in ramie root increased with increasing concentration of Cd,and Cd absorbed mainly in the root,moreover,the operating factor of Cd in ramie was reduced with the increasing of Cd stress.The operating factor of three types of ramie was only between 0.13-0.23,but the accumulation of cadmium in root could reach 278-1389 mg kg-1 dw.At 3,6,9 mg L-1 Cd stress,the operating factor of three types of ramie were dropped to 0.139,0.144,0.130 from 0.227?0.211?0.180.this result meant that mainly Cd absorbed stayed in root,which have more patience to heavy metal stress,is one of the important mechanisms of Ramie to defend cadmium stress.3)Cd stress can rapidly induce the production of endogenous spermidine,proline ramie and other substances.These special substances could protect ramie from free radicals caused by oxidative stress,and reduce moisture loss and other physiological persecution.It means that cadmium stress can effectively induce cells to produce specific physiological,activating anti-cadmium stress defense mechanisms,also one of the important physiological mechanisms of resistance to cadmium.4)Ramie can effectively fixed a large number of cadmium,reduced the liquidity of heavy metal pollution,and prevent the diffusion and poison to more large land,which is an important way of phytoremediation.However,it also means that there has quite high concealment,which remind peoples to pay more attention to the apply of ramie in phytoremediation.5)This paper preliminary discussed the physiological response of the ramie under cadmium stress,and Laid a solid foundation of test conditions and materials for the next part of the test.Due to the discuss and analysis,ramie with deep root have more larger growth,more larger Cd accumulation,littler influence of cell membrane under Cd stress,more stronger ability to defend heavy metal stress,especially under the high high concentration of cadmium stress.6)Proper concentration of selenium can effectively improve the resistance of ramie to cadmium stress,but a high concentration of selenium also have more deleterious effects on ramie.Whit spraying Se concentration at 1.2 ?M,chlorophyll content increased by 14.70%and 36.49%,the MDA content decreased by 20.32%and 8.97%in ramie root,MDA content decreased by 15.68%and 15.05%in leaf,respectively,and the ramie leaf cell membrane permeability is slight relief,at o and 6 mg L-1 Cd stress.When spraying with 1.8?M Se,ramie shown more fragile to Cd stress and more harmful to the growth.The chlorophyll content in ramie leaf reduced by 8.40%and 8.32%,the MDA content increased by 9.80%and 9.82%in ramie root,MDA content decreased by 9.45%and 15.50%in leaf,respectively,and the ramie leaf cell membrane permeability is also increased by 7.48%and 12.75%,at o and 6 mg L-1 Cd stress.7)The content of chlorophyll,and the activity of SOD and POD increased under low concentrations of Cd,but decreased significantly under high concentrations,including the content of MDA.Compared with separately treating 3,6 and 9 mg L-1 Cd,when ramie plants were sprayed simultaneously with low Se,the activity of SOD and POD increased by 35.34%,43.18%,3.63%and 12.45%,14.14%,3.27%.the level of DNA methylation was decreased by 10.70%,18.18%and 15.59%.8)Based on the previous studies and the present experiment,the alleviation mechanism of exogenous Se on ramie plants exposed to Cd stress may include:?reduction of the absorption and accumulation of Cd,and removal of Cd from metabolically active cellular sites;?reduction of oxygen radicals by antioxidant enzymes;and?effect of maintaining the stability of DNA methylation.