| Facing the conditions that the soil environment under the threaten of Bensulfuron-methyl (BSM) and cadmium (Cd) due to the widely using of sulfonylurea herbicides and the continuously releasing of heavy metal elements in our country, as well as the toxicity mechanism of BSM and Cd still remaining a tantalizing but unsolved puzzle, this study investigated the toxicity mechanism of the rice under the co-contamination of BSM and Cd from the individual level, cellular level and the molecular level by employing the rice of Feng Maizhan and Yue Xingzhan as the indicator plants. The results can not only enrich and develop the toxicological theories of environmental pollution, but also provide the scientific basis for controlling pollution and making environmental quality standard.First, the results in individual level indicated that with increasing Cd concentration, the biomass of the rice, the chlorophyll content and activity of catalases (CAT) reduced in a dose dependent manner with notable differences (p<0.01), and solution conductivity increased with increasing of Cd content. The data showed that the tolerance of Yue Xiangzhan to Cd was higher than that of Feng Meizhan. It could relieve the toxicity of Cd when the concentration of BSM in the extension of 0.1 mg·L-1 and 0.2 mg·L-1. The biomass, the chlorophyll content and the CAT activity significantly decreased when the concentration of BSM exceeded 0.6 mg·L-1. However, the concentration of BSM did not affect the solution conductivity significantly. The ICP was used to determine the accumulation of Cd in the root and shoot of the rice. The data illustrated that the accumulation of Cd in root was about 6-fold than that in shoot. When the concentrations of Cd were 50 mg·L-1 and 300 mg·L-1, applying 0.1 mg·L-1 and 0.2 mg·L-1 BSM could decrease the uptake of Cd. However, when the applied BSM was more than 0.4 mg·L-1 the accumulation of Cd in root was dramatically increase, but there was no significant difference for the uptake by stem. This meant that BSM inhibited the transference of Cd from root to shoot. In conclusion, although the toxicity of Cd to the rice could be relieved when 0.1-0.2 mg·L-1BSM treatments were applied, it would be more toxic to rice when the concentration of BSM exceeded 0.6 mg·L-1 and coexisted with Cd.Furthermore, the results in cellular level by scanning electron microscope (SEM), transmission electron microscope (TEM) suggested that the co-contamination of BSM and Cd could lead to cellular structure destroying, epidermic cells disrupting and nucleolus resolution. There were mass of phenolics in the cell due to the stress for environment. In addition, some unknown substances which are supposed as complexes of BSM and Cd deposited on the margin and interior of cytoderm. The epidermic cells of untreated rice were smooth and intact, whereas the epidermic cells under the co-contamination of BSM and rice were destroyed and rough.Finally, the results in molecular level by comet assay, RAPD and RT-PCR indicated that Cd had a strong genotoxicity to rice. Cd could not only change the images of comet assay but also the RAPD profiles. BSM could damage the rice genome, however, BSM could relieve the toxicity of Cd to rice genome in a certain concentration range. OsMRP3 could not be upregulated by BSM and Cd alone, however, it could be upregulated when Cd and BSM co-existed. Above all, the results showed that BSM and Cd could produce poisonous effects to rice from individual, celluar and molecular levels. Although the toxicity of Cd to the rice could be relieved when 0.1-0.2 mg·L-1 BSM treatments were applied, it would be more toxic to rice when the concentration of BSM exceeded 0.6 mg·L-1 and coexisted with Cd. The expression of OsMRP3 could only be upregulated when the BSM and Cd coexisted. |
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