Effects Of The Dual Stress Of UV-B And Cadmium On Ecological Parameters Of Wheat And Sitobion Avenae(Hemiptera: Aphididae)

With the rapid development of industry, the depletion of stratospheric ozone layer has led to an increase in the levels of potentially harmful UV-B radiation reaching the surface of the earth. At the same time, unreasonable exploitation of mining, irrational using of chemical fertilizer or pesticide and emission of large amounts of production and living sewage have led to a sharp accumulation of heavy metal Cd in the environment. So, UV-B radiation and Cd become the main factors of environmental pollution, recently. And, they generate strong selection pressure for ecological environment and the development of plants, animals and microorganisms; Thus, they are threatening the ecological balance. UV-B radiation or heavy metal(Cd) has been reported to elicit secondary substances in plants or animals, and influence their physiological and biochemical metabolism, growth, development and reproduction. However, the mechanism about plants or animals exposed to the dual stress of UV-B radiation and Cd has not been reported. Wheat is not only the main food crops in China, but also in the world. However, Sitobion avenae(Fabricius) is one of the most important pests in wheat, and can cause wheat yield reduction and even totally yield losts. Because S. avenae is a r strategist, it can quickly adapt to the changes of environmental conditions. So, S. avenae is a very good material to study the environmental changes in the laboratory. Many previous studies have been reported about the effects of the stress of UV-B radiation or cadmium on secondary metabolites, physiological and biochemical metabolism, growth, development and fecundity of plants and animals. But, little studies have been reported about defense mechanism of plants and animals under the dual stress of UV-B radiation and cadmium. However, these two stress factors of UV-B radiation and cadmium are coexisting in the real environment. But, the biological effects of the dual stress of UV-B and cadmium on the population of insects are still unclear. So, this study was conducted under laboratory conditions. It simulated natural environment to study the changes of life table parameters and the activities of antioxidant enzymes and glutathione-s-transferase(GSTs) of S. avenae exposed to the stress of UV-B radiation and Cd,in order to explore the effects of ecological parameters of S. avenae under the stress of UV-B radiation and Cd. Moreover, the study of effects of the dual stress of UV-B and Cd on S. avenae ecological parameters can establish foundation to the research of adaptation and defense mechanism of S. avenae exposed to the stress of UV-B radiation. And, it also has great significance to adaptation mechanism, genetic evolution, forecast the dynamics and integrated pest management of S. avenae under the change of environmental conditions in the new period.The following are the main results of study:1) At a certain range, the concentration of Cd in the above ground part of wheat seedings nonlinearly increased with increasing Cd levels in soil. The following quadratic regression equation was established through correlation analysis of concentrations of Cd in soil and above ground part of wheat.The nonlinear relation(R2=0.9993) was notable between the concentrations of Cd in soil and the above ground part of wheat seedings. The results showed that the concentration of Cd in S. avenae was nonlinearly increased with increasing Cd levels in soil. At the same time, it was consistent with the change of concentration of Cd in soil.2) The activities of antioxidant enzymes in wheat could be significantly improved by the stress of UV-B radiation and Cd. The contribution rate of UV-B radiation on the activities of peroxidase(POD) and catelase(CAT) were bigger than Cd, while the contribution rate of Cd on the activity of total superoxide dismutase(T-SOD) was bigger than UV-B radiation. At the same time, the effects of UV-B radiation and Cd had interaction. Therefore, the effects of the stress of UV-B radiation and Cd on the activities of the above 3 kinds antioxidant enzymes in wheat was the more significant than that exposed to a single stress, UV-B radiation or Cd. It was concluded that the effects of activities of antioxidant enzymes in wheat exposed to UV-B radiation with Cd was more notable than that exposed to the stress of UV-B radiation or Cd.3) S. avenae exposed to the dual stress of different intensities of UV-B radiation and different concentrations of Cd for a short time or a whole generation has influence on life table parameters of S. avenae population in varying degrees. And, the greatest degrees influence would be appear when the stress intensity of UV-B radiation was 0.2m W/cm2 and the stress concentration of Cd in soil was 40 mg/kg. Moreover, the effects of two factors between UV-B radiation and Cd had interaction. It was showed that life table parameters of S. avenae were notably affected by the stress of UV-B radiation and Cd, and the influences would be intensified when the two factors acted in combination.4) The activities of antioxidant enzymes and glutathione-s-transferase(GSTs) in S. avenae were significantly affected by stress of UV-B radiation and Cd for a whole generation. The contribution rate of UV-B radiation on the activities of peroxidase(POD) and catelase(CAT) were greater than Cd, while the contribution rate of Cd on the activities of total superoxide dismutase(T-SOD) and glutathione-s-transferase(GSTs) were greater than UV-B radiation. At the same time, the effects of UV-B radiation and Cd had interaction. Therefore, the effects of the stress of UV-B radiation and Cd on the activities of the above 4 kinds protective enzymes in S. avenae were more significant than that exposed to a single stress, UV-B radiation or Cd. It was concluded that the effects of activities of these 4 kinds protective enzymes in S. avenae exposed to UV-B radiation with Cd was more notable than that exposed to the stress of UV-B radiation or Cd.In conclusion, life table parameters of S. avenae on wheat under the stress of UV-B radiation and Cd were significantly affected. Moreover, S. avenae could adapt and compensate the damage of UV-B radiation and Cd through inducing and regulating the expression of protective enzymes of wheat and S. avenae. S. avenae could adapt the stress of UV-B radiation and Cd by changing or regulating their ecological parameters to maintain the stability of internal environment and benefit to the continuation of the population.