Response And Enrichment Of Plants To Uranium Stress Under Low Voltage Electric Field

The ecological risk of uranium pollution will increase with the rapid development of the nuclear industry.Phytoremediation is proposed as a benign technology to deal with in-situ area source uranium pollution,but the remediation efficiency is low.The effect of low voltage alternating current?AC?and direct current?DC?electric fields on the growth,physiological and biochemical responses and uranium enrichment ability and characteristics of amaranth?Amaranthus tricolor L.?and sunflower?Helianthus annuus L.?were studied in water with uranium.The results are as followed:?1?At 0.5 or 5.0 mg U·L^-11 for 21 days,the malondialdehyde?MDA?,relative conductivity and peroxidase?POD?activity of amaranth were significantly increased?P<0.05?,while chlorophyll a,b and carotenoid,net photosynthetic rate?A?,intercellular carbon dioxide concentration?Ci?and water use efficiency?WUE?,catalase?CAT?and superoxide dismutase?SOD?activity,soluble protein and proline?Pro?,and the length of root decreased significantly?P<0.05?,indicating that uranium had obvious oxidative stress on amaranth,therefore causing the decline in the photosynthetic ability and osmotic adjustment ability of amaranth to some extent,which was positively correlated with uranium concentration.The uranium was mainly accumulated in the roots of amaranth at a maximum accumulation amount of 5.72 mg·g-1 DW,positively correlating with uranium concentration.Only no more than 2%of root uranium could be transferred to aboveground part.Under the same uranium treatment conditions,the addition of 0.25 V·cm^-11 DC electric field would cause further significant decrease in chlorophyll a and root length of amaranth.The maximum photochemical efficiency?Fv/Fm?and POD activity of the DC treatment group were also significantly lower than that of the uranium control group at same uranium concentration?P<0.05?,indicating that the application of DC electric field may further aggravate the uranium stress on amaranth.However,the MDA and relative conductivity also decreased,while WUE,SOD activity,and the A,transpiration rate?E?,CAT activity and soluble protein at the higher uranium concentration increased significantly?P<0.05?,indicating that the physiological and biochemical responses of amaranth to DC under uranium stress are complex and further study is necessary.In addition,without changing the uranium enrichment characteristics of amaranth,the DC application significantly reduced the uranium accumulation in root of amaranth,and promoted the ability to transport and enrich to the leave.Under the same uranium treatment conditions,after adding 0.25,0.50 V·cm^-1AC electric field,the MDA of amaranth decreased significantly,while A,stomatal conductance?Gs?,E,root length and fresh weight increased significantly?P<0.05?,which indicated that AC might alleviate the stress of uranium on amaranth to some extent.In addition,AC did not change the enrichment characteristics of amaranth,but significantly increased the uranium accumulation of root?P<0.05?.The 0.25 V·cm^-11 AC had better performance on uranium enrichment.Compared with the uranium control group,the uranium content in root,stem and leave root-stem transport coefficient of amaranth were1.35,4.19,3.62,3.11-fold respectively at 5.0 mg·L^-11 uranium and 0.25 V·cm^-11 AC.?2?At 5.0 mg U·L^-11 for 21 days,the MDA and relative conductivity of sunflower were significantly increased?P<0.05?,which indicated that uranium resulted in some oxidative stress on sunflower.However,the improved antioxidant enzyme activity,and increased photosynthetic pigments and soluble sugar might promote the growth ofroot length,plant height and biomass of sunflower.Uranium enrichment of sunflower was mainly in root,maximumly reaching to 3.31 mg·g^-11 DW,which was lower than that of amaranth in the same uranium concentration.Under the same uranium treatment conditions,the addition of0.25 V·cm^-11 DC electric field would significantly reduce the MDA and relative conductivity of sunflower,as well as the photosynthetic pigment,A,root length,plant height and biomass?P<0.05?,indicating that the application of DC electric field may decrease photosynthetic capacity and inhibit its growth.In addition,similar to the amaranth,without changing the uranium enrichment characteristics of sunflower,DC significantly reduced the uranium enrichment in root of sunflower,while promoted the ability to transport uranium to the leave?P<0.05?.Under the same uranium treatment conditions,after application of 0.25,0.50V·cm^-11 AC electric field,the MDA of sunflower decreased significantly,while the relative conductivity increased significantly,and only the high voltage group significantly promoted the accumulation of biomass?P<0.05?,which indicated that AC has alleviated the oxidative stress of uranium on sunflower to some extent.In addition,AC also did not change the uranium enrichment characteristics of sunflower,but significantly promoted the ability of the enrichment and transport of uranium by root,stem and leave?P<0.05?,and 0.25 V·cm^-1AC had a more significant effect on uranium enrichment of sunflower,same as amaranth.Compared with the uranium control group,the uranium content in root,stem,leave and root-stem,stem-leaf transport coefficient of sunflower with AC were 1.30,4.76,8.05,3.66,1.70-fold respectively.The results showed that uranium contaminant would cause oxidative stress on plants,which would further damage the photosynthetic capacity and osmotic adjustment ability of plants.Uranium was mainly accumulated in root of plants.At the same concentration,sunflower was more tolerant to uranium than amaranth,while the enrichment of uranium by amaranth was greater than sunflower.The application of AC electric field not only alleviated the uranium stress on plants to a certain extent,but also significantly promoted the enrichment ability of root,and the effect of 0.25 V·cm^-11 treatment is more significant.