| In recent years,the development of China’s industry has been very rapid,and the economy has increased at a high speed.At the same time,the pollution to the natural environment has also increased.Humans have adopted a variety of repair methods for the treatment of heavy metal environment,among which phytoremediation has become a research hotspot.Amaranthus caudatus,an annual herb of Amaranthaceae and Amaranthus L.,was used as experimental material in this experiment.Through the method of hydroponic and soil culture with different concentrations of cadmium treatment on seed germination,physiological characteristics of seedlings at different stages,cadmium enrichment regularity and DNA methylation changes in organs were studied.The preliminary studies on physiological characteristics of plants polluted by heavy metals after adding different concentrations of citric acid under the same cadmium concentration treatment,providing a theoretical basis for complex phytoremediation of heavy metal contaminated plants.The results are summarized as follows:1.Effects of cadmium stress on seed germination and seedling growth of Amaranthus caudatus: Amaranthus caudatus showed a phenomenon of "low promotion but high inhibition" under different concentrations of cadmium stress,that is,low concentration of cadmium treatment promoted the germination of Amaranthus caudatus seeds,while high concentration of cadmium treatment inhibited the germination of seeds.The germination rate under cadmium stress reached above 90%,and the highest germination rate was 98.90% when cadmium concentration was 50 mg/L.The root length and seedling length of amaranth treated with cadmium were both lower than those of control group(0 mg/L),and the root length and seedling length were negatively correlated with cadmium treatment concentration.2.Effects of cadmium stress on physiological resistance of Amaranthus caudatus: the physiological indexes of Amaranthus caudatus under different concentrations of cadmiumstresses in different growth stages were measured and analyzed.The results showed that:(1)With the increase of cadmium concentration the activities of SOD,CAT,POD and soluble protein content in Amaranthus caudatus showed a trend of increasing first and then decreasing,and reached the maximum when the concentration of cadmium was 100 mg/L.(2)the chlorophyll content of plants decreased with the increase of cadmium concentration,and the chlorophyll content in vivo was lower than that in the control group.(3)The cadmium stress treatment resulted in the increase of Pro content and MDA content in Amaranthus caudatus at all stages,and the overall trend was upward with the increase of cadmium concentration.3.Study on physiological resistance of Amaranthus caudatus under cadmium stress by adding exogenous citric acid: Amaranthus caudatus was treated with the same cadmium concentration(100 mg/L)and then added different concentrations of exogenous citric acid for processing.The results showed that: With the increase of citric acid concentration,oxidase activity(SOD,POD,CAT)and chlorophyll content showed a trend of increasing first and then decreasing,while MDA content and Pro content decreased first and then increased,but both of them were lower than that of the control group(0 mmol/L),indicating that the addition of exogenous citric acid can withstand relatively high concentration of cadmium stress and play an active role in resisting cadmium stress injury.4.Study on cadmium accumulation in Amaranthus caudatus under cadmium stress: the cadmium content and soil cadmium content in amaranth under different concentrations of cadmium stress were determined and analyzed.The results showed that: The accumulation of cadmium on aboveground and underground parts of Amaranthus caudatus increased with the increase of cadmium concentration,and there was a significant positive correlation between cadmium concentration in plant and cadmium concentration in soil.Under cadmium stress,the total concentration of the aboveground part of Amaranthus caudatus is higher than the underground part,and the enrichment rule was root > leaf > stem > flower,and the enrichment coefficient and transfer coefficient are greater than 1,which indicates that the plant is a super-accumulative plant of heavy metal cadmium,it can significantly reduce the heavy metal content in soil,reducing the level of heavy metal pollution can be effectively play the role of repair of soil heavy metal pollution.5.Effects of different concentrations of cadmium stress on DNA methylation of Amaranthus caudatus: The changes of DNA methylation of Amaranthus caudatus genome under cadmium stress were analyzed by MSAP technology.The results showed that: After treatment with 0,50,100,150 and 200 mg/L cadmium concentration,the total methylation rates were 13.49%,14.35%,14.41%,14.88% and 15.69%,respectively.The total methylation ratios were 17.21%,20.18%,20.96%,21.49% and 22.35%,visible after processing,the heavy metal stress under cadmium stress tail preharvest CCGG sites Amaranthus caudatus genome methylation is the main full methylation on the way,and DNA methylation level always is on the rise with cadmium concentration.In terms of changes in DNA methylation patterns,under the stress of 50,100,150 and 200 mg/L,the rates of re-methylation were 5.83%,7.42%,9.50%,10.98% and the rates of de-methylation were 6.73%,5.68%,4.96% and 3.53%,respectively.It is concluded that the ratio of re-methylation and de-methylation is increasing continuously,indicating that the level of re-methylation of Amaranthus caudatus shows an upward trend under the induction of heavy metal cadmium.Re-methylation is the dominant methylation mode. |
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