Studies On Toxic Responses And Mechanism Of Resistance In Conyza Canadensis To Cu Stress

Today, with rapid development of society and economy, heavy metal pollution has been an international difficult problem, especially, mine wasteland pollution is serious, many countries have endeavored to clear away it. many heavy metals are essential chemical elements that plants grow, for example Copper, but when the metal contents of soil are higher than some a critical value, they will become pollution. This pollution will bring serious results, it does much harm to kinds of plants, disturbs normal physiological metabolism of plants, affects their growth, development and reproduction. In despite of these, many species can grow naturally in soil with heavy metal pollution, and that accumulate heavy metal. they show themselves resistance to heavy metal. So we should study these tolerant plants and utilize them to clear out pollution in soil, and that rehabilitate largely mine wasteland. In this paper, through field surveys and mensuration on the communities and dominant plants of copper tailing mine wasteland in Shizhishan, Tongling, Anhui Province, The results showed that soil in wasteland was extreme infertile, heavy metal pollution was very serious(especially ,the concentration of Cu and Cd is 30 times as that in the normal soil),community structure was very simple(mainly composed of five seral communities types), dominant plants mostly belonged to Compositae, Graminese, Leguminesae and H.ramosissimum of Equisetaceae,of which Graminese is rarely studied,so Conyza Canadensis with big biomass in Graminese was used as test sample to study its resistance mechanism to copper. Conyza Canadensis is one-year plant with strong root and big biomass, primely adaptive to bad environment, widely arranges in Anhui, so it has well developmental potential and wide applied value in phytoremediation of mine wasteland. Through further potted experiment and mensurating physiological, ecological and biochemical indexes of Conyza Canadensis, the results showed that under low concentration of Cu (400mg.kg^-1), Conyza Canadensis didn′t put up evident poisonous symptoms but showed itself a good growth, while exposed to high concentraion of Cu (800-1500mg.kg^-1), Conyza Canadensis took on serious harmful symptoms as followings: First,a large number of ROS(produced and accumulated in plant)damaged severely the cytomembrane, cytoarchitecture and function of main organelles,disturbed its physiological metabolism and critically made threat to its normal growth.Sencond,copper restrained pigment content of leaf and destroyed function of chlorophyll so to affect photosynthesis of plant.Third,different populations of the same species were largely variant in sensitivity to Cu stress,popularly,the tolerance of plants chronicly growing in high concentration of Cu exceeds that living in unpolluted area. In the long-term of adaption and evolution,the resistance mechanism of Conyza Canadensis to Cu stress was formed,which safeguarded its growth and reproduction. This mechanism was made up of as followings: Firstly,the protective enzyme activities were enhanced,especially the increase and maintenance of SOD, POD and CAT could clean up the active-oxygen (cumulation in plants) so to reduce the toxicity to plants.Secondly,mass of Cu was intercepted in root and accumulated in cytoderms,so this reduces the transportation and toxicity of Cu in plants.Thirdly,there mostly existed in less activate extractable-Cu forms,less dissociative Cu²⁺ in plant, so this enhanced the resistance of the plant to Cu stress.Fourthly, small molecule substances as Citric acid , Oxalic acid and Reduced glutathione for injection are also studied,they could combine dissociative Cu²⁺ and reduce its toxicity,but their detailed functions are necessarily further studied.