Mechanism Of Cesium Clearance And The Accumulation Characteristics In Brassica Juncea And Cichorium Intybus

With the development of nuclear and nuclear technology and the widely used of radionuclide, control radionuclide pollution has become one of the contemporary environment problems. Radiocesium contamination of the global environment has resulted from nuclear testing and nuclear technology emissions, 137 Cs with a relatively half-life of 30.17, has been the most harmful radioactive nuclide. The presence of radiocesium in water, soil and atmosphere posed threats to populations inhabiting in the contaminated environments. The earlier studies have suggested that Cs⁺ may be absorbed by plants in a competitive fashion with potassium（K+）, with belongs to the same alkali metal group and shares similar chemical properties with Cs⁺. Cs⁺ has no known beneficial function in plants, however, it can concentrations cause toxicity at high concentrations, observed as growth inhibition. Thus far, Cs⁺ uptake characteristics and clearance mechanism in plants have not been thoroughly.In this study, Brassica juncea and Cichorium intybu were used as materials, seedlings at the two leaf stage were subjected to varying doses of Cs⁺ [ρ（Cs⁺） 0²00 mg·L^-1] for 48 h to 9 days. Then, the dry biomass, the content of Cs, H₂O₂, O₂^-, GSH, NPT, PCs and MT in over-ground, root was analyzed, respectively.The main findings are as follows:（1）The same processing time, the dry biomass of over-ground and root decreased in two plants with the increase of Cs⁺ concentration（P<0.05）.The dry biomass of over-ground in Brassica juncea and Cichorium intybu were decreased 2.35%⁵.56%（48 h）, 5.00%¹3.98%（9 d） and 1.87%⁸.88%（48 h）,10.93%³9.55%（9 d）; the dry biomass of root in the accumulation content of Cs and Cichorium intybu were decrease 3.76%¹8.34%（48h）,4.99%¹4.25%（9d） and 1.06%¹0.90（48 h）, 11.9%³1.43%（9 d）.However, degree of dry biomass are inhibited for Cs following Cichorium intybu>Brassica juncea. In a short period of time（48 h）, the dry biomass showed a reduced rate of the root>over-ground; but along with the prolonged（9 d） degree dry biomass showed a reduced of root≈over-ground.（2）With the increase of Cs concentration, the accumulation content of Cs in two plants increased significantly（P<0.05）. In the same processing time, the accumulation content of Cs in Brassica juncea was increased 91.4 ¹48.4（24 h）, 243.20⁵05.20（48 h） in over-ground, and 105.2¹30.4（24 h）, 121.20³85.00（48 h） in root.The capacity of accumulation for Cs⁺ showed: Brassica juncea > Cichorium intybu. The root of Cichorium intybu is the mainly accumulation organ for Cs, but the over-ground of Brassica juncea is the mainly accumulation parts.（3） Different concentrations of Cs⁺ be able to impact Brassica juncea and Cichorium intybu oxidation and antioxidant systems. In the same processing time, with the increase of Cs⁺ concentration the contents of H₂O₂ in two plants were first increasing and then decreasing, these content of two plants maximized when the concentration of Cs reached 100 mg·L^-1. Further analysis shows that over-ground had a higher content than roots in two plants, and Cichorium intybu had a higher content than Brassica juncea seedlings. With the increase of Cs concentration, the content of O₂^- in two plants increased significantly（P<0.05）. These content of two plants maximized when the concentration of Cs reached 200 mg·L^-1. And all showed tha over-ground had a higher content than roots in two plants, and Cichorium intybu had a higher content than Brassica juncea seedlings. ROS, DAB and NBT dyeing, according to the results of two dyeing plant leaves with the increase of the concentration area and color deepened, it is consistent with the results of content determination. with the increase of Cs⁺ concentration the contents of GSH in two plants were first increasing and then decreasing, these content of two plants maximized when the concentration of Cs reached 100 mg·L^-1. Further analysis shows that over-ground had a higher content than roots in two plants, and Cichorium intybu had a higher content than Brassica juncea seedlings.（4） With the increase of Cs, the content of non-protein thiol（NPT）、PCs and MT were first increasing and then decreasing, these content of two plants maximized when the concentration of Cs reached 100 mg·L^-1. The content of NPT in Brassica juncea was increased 8.14%³0.67% in over-ground,and 5.35%³4.53% in root, Cichorium intybu was increased 13.64%³6.42% in over-ground, and 5.59%²4.98% in root; Brassica juncea over-ground and root PCs content was increased 22.2%³0.7% and 19.3%⁶5.5%; the content of MT in Brassica juncea was increased 16.02%¹9.93% and 10.15%³0.16%.Further analysis shows that roots had a higher content than over-ground in two plants, and Brassica juncea had a higher content than Cichorium intybu seedlings.In conclusion, the tolerance of Cs in Brassica juncea was higher than Cichorium intybu. The mainly reason is that Cs can significantly induce the synthesis of PCs, GSH and MT in Brassica juncea when the seedlings accumulated excessive.