| Recent years,a large amount of Uranium?U?-contained water was released to the environment as the function of the rapid development of nuclear industry,and therefore cause a potential hazard for the human health and eco-environment.Compared with the traditional physical and chemical method,phytoremediation takes the advantages of low cost,environment friendly,and high public acceptance,whereas it has the defects of slow growth and low efficiency of remediation.Previous studies have shown that the external low-voltage electric field could promote the accumulation capacity of heavy metals by plants.In this study,the Eichhornia crassipes was used as the target biology,the effects of U concentration,electric field intensity,electrified time and the microbial agents on the physiological and biochemical responses of uranium-contamination and its uranium accumulation capacity as well as characteristics were investigated via testing the concentration of antioxidant enzymes,proline?Pro?,malondialdehyde?MDA?,chlorophyll,chlorophyll fluorescence,as well as the distribution of U in the plant,results showed that:When the concentration of U was higher than 5 mg·L-1,the MDA content of E.crassipes increased with the increasing of the U concentration,indicating that the plant suffered higher oxidative stress.This trend was not impacted by the external electric field,and the content of MDA in each group was much higher,indicating that the electric field may further aggravate the oxidative stress on plants.With the increasing of U concentration,the content of Pro in E.crassipes showed a positive correlation,while the activities of peroxidase?POD?,catalase?CAT?and chlorophyll increased firstly and then decreased,indicating that E.crassipes could suit for the oxidative stress by adjusting the osmotic regulation and antioxidant capacity of plant.However,the improvement of plant resistance to oxidative stress was related to the stress of U.The external electric field did not change the trend of these indicators affected by U concentration,but the osmotic regulation and antioxidant capacity of plants was enhanced significantly.In addition,U was mainly accumulated in the roots,the higher U concentration is,the higher U accumulation capacity is(with the highest accumulation under 50 mg·L-1 U).External electric field could significantly promote the accumulation of U in the roots of the E.crassipes.The maximum concentration of uranium in the roots of the E.crassipes reached 1.311 mg·g-1 DW at the concentration of 50 mg·L-1 U,which is 7 times that of the electric-field-free samples.Totally,the electric field improved the accumulation capacity of U in E.crassipes roots,and promoted the tolerance of U by improving the activity of antioxidant enzymes and the synthesis of Pro.despite increased the tolerance of plants to uranium stress.Under the 10 mg·L-1U conditions,the higher external electric field is,the higher MDA content of E.crassipes,indicating that oxidative stress was positively correlated with electric field intensity.While the electric field intensity was less than 0.75V·cm-1,the activities of CAT,POD and the content of Pro increased significantly,which was positively correlated with electric field intensity,and decreased when the electric field intensity was higher than 0.75 V·cm-1.The chlorophyll content and SOD activity were positively correlated with the intensity when the applied electric field intensity was less than 0.5 V·cm-1,and then decreased.Furthermore,compared with the electric-field-free samples,the U were mainly accumulated in the root of E.crassipes with2.3-4.2 times accumulation capacity in different electric field intensities,and reached the maximum value of 0.610 mg·g-1 DW when the electric field intensity was 0.5 V·cm-1.Herein,the higher electric field intensity is,the greater extent of oxidative stress of plants will be under uranium stress.Comprehensively viewed,when the electric field intensity in the range of 0.5-0.75 V·cm-1,the osmotic regulation ability and antioxidant capacity of plants can be significantly promoted,thus improved the tolerance of plants to uranium.The accumulation capacity of U in the E.crassipes root could be promoted by different the electric field intensities with the maximum accumulation capacity when the electric field intensity was 0.5 V·cm-1.When the external electric field was applied for 2-10 h/d,within 1-day,the MDA content of E.crassipes was increased with the increasing of applied time of electric field,the activities of POD,SOD and CAT antioxidant enzymes increased first and then decreased with the increasing of applied time,but all were higher than the control samples,the content of Pro is positively correlated with the applied time of electric field.After 5 days of continuous exposure,the content of MDA and the activity of SOD in the plants decreased with the application time of 2h-8h/d electric field compared with the electric-field-free control samples?Under the U stress?.The accumulated U was mainly concentrated in the roots of all plants.Under the electric field treatment time of 4h-8h/d,the accumulation of U in the roots was relatively high compared with other sections with the maximum value of 0.401 mg·g-1 DW.In conclusion,the application time of electric field has an effect on the capability to uptake uranium and the ability to tolerance stress of E.crassipes.The application time of 4 h-8 h/d electric field is more effective to promote the capability of uranium accumulation of plants.Under the external electric field and U stress,the application of low concentration microbial reagents had rare significant effect on the MDA content of E.crassipes,while the high concentration microbial reagents could result the increase of MDA content in plants,and the longer the treatment time is,the greater the increase is.Generally speaking,the application of microbial reagents can facilitate the enzyme activities of CAT,POD and SOD,thus improve the tolerance of plants to oxidative stress.The effect of high concentration of microbial reagents is better than that of low concentration of microbial reagents,Bacillus subtilis is better than the effect of EM mixed bacteria.However,the application of microbial reagents inhibited the production of Pro on within the 1st day,and promoted the production of Pro on the5th day.High concentration of B.subtilis had the best effect than that of low concentration samples.Besides,the application of microbial reagents could further promote the accumulation of U in the roots of E.crassipes,and the higher the concentration of microbial reagents is,the greater the accumulation capacity of U is?with 339%times than the control sample?.Herein,the most significant effect of high concentration of B.subtilis.Therefore,the application of 1.0×107 cfu·mL-1 B.subtilis could better to improve the accumulation of U and adaptability of E.crassipes. |
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