| In recent years, there is a growing concern over the pollution of heavy metals in China owing to rapid urban and industrial development. The release of heavy metals, into the water and soil is known to affect the growth and development of plants, then insects accumulate heavy metals by eating plants. Oxya chinensis is one of the most important agricultural pests, the major food of Oxya chinensis are rice, wheat, corn, and so on. Under the stress of heavy metals pollution, Oxya chinensis accumulates heavy metals and excretes part of them through the feces and exuviates. It was demonstrated that antioxidant defense system and the metabolic detoxification enzymes play an important role in resistance to heavy metals. Further exploration of heavy metals accumulation and metabolism in Oxya chinensis could provide the basis for monitoring heavy metals pollution in the agricultural environment.The main contents of this thesis were:1) Oxya chinensis were fed on polluted wheat seedlings from3rd instar nymphs. The atomic absorption spectrophotometer was used to measure Cd concentrations in wheat seedlings and Oxya chinensis. Determination of the hemolymph biochemical compositions and energy changes of Oxya chinensis after chronic exposure, analysed the relationship between the Cd accumulation and hemolymph biochemical compositions.2) The4th instar nymphs were injected into different Cd2+and Cr6+concentration solutions, biochemical compositions and energy changes of hemolymph were assayed.3) Metabolic detoxification enzymes and polyphenol oxidase activities were determined by spectrophotometericaliy after the insects exposed to chronic toxic food. This work could improve our understanding of the relationship between Cd accumulation and enzyme activity.4) The present study aimed to analyze the relationship between Cd accumulation and enzyme activity by acute exposure to Cd in the4th instar nymphs of Oxya chinensis.The results of this study showed that:1) The wheat seedlings were cultured by different concentrations of Cd solutions (0,10,20and40mg-L-1), the corresponding Cd concentrations of wheat seedlings leaves after7days were:0,2.62±0.3,6.32±0.76and13.38±1.46mg·kg-1dry weight. There was a positive correlationship between the Cd concentrations of wheat seedlings leaves and Oxya chinensis. A significant decrease in contents of either soluble protein, caloric values or sugar in the hemolymph occurred due to the increasing of the Cd concentrations; compared with the control, the lipid contents decreased while Cd concentrations of wheat seedlings leaves were2.62mg-kg-1and13.38mg-kg-1.(2) The present study aimed to analyze and compare the biochemical compositions and energy changes in the hemolymph induced by acute exposure (24、48、72and96h) to Cadmium chloride solution (0、3.54、7.08mg·kg-1) and chromium hexavalent solutions (0、1.80、3.40mg·kg-1) in the4th instar nymphs of Oxya chinensis. The results showed that the sugar contents and caloric values in hemolymph had no significant changes. The soluble protein contents decreased in24h and48h, lipid contents increased compared with the control in72h and96h. The hemolymph compositions and energy levels were increased both in low concentration (1.80mg·kg-1) and high concentration (3.40mg·kg-1).3) The activities of carboxylesterase (CarE), acid phosphatase (ACP), alkaline phosphatase (AKP), glutathione S-transferase (GST), and polyphenol oxidase (PPO) were measured after a chronic exposure to toxic food in Oxya chinensis. Activities of the CarE, AKP, GST and PPO indicated that it was increased with the increasing Cd, and the ACP activity without significant changes. The results showed that, Oxya chinensis can resist to the toxic effect of Cd by increasing the activityies of metabolic detoxification enzymes and polyphenol oxidase.4) Activities of metabolic detoxification enzymes and polyphenol oxidase induced by acute exposure (24h,48h,72h and96h) to Cd and Cr in the4th instar nymphs of Oxya chinensis were analyzed. The results showed that the CarE activity measured against a-NA of high concentrations of Cd was activated in48h, and CarE activity was activated by Cr in72h; the CarE activity measured against a-NB of high concentrations of Cd was activated in72h, and CarE activity was activated by Cr in24h and72h; The ACP activity in96h was inhibited by Cd. The ACP activity increased in low concentrations of Cr, reduced in high concentrations of Cr in24h and48h. AKP activity increased in72h after the treatments of Cr, GST activity increased by Cd in48h and by Cr in72h and96h. PPO activity reduced after Cd treatment for96h and Cr treatment for24h.Above all, the heavy metals resulted in changes of hemolymph biochemical composition, energy levels, and affected the activities of metabolic enzymes and polyphenol oxidase in Oxya chinensis. These changes reflected defense mechanisms of Oxya chinensis. This thesis analyzed the hemolymph energy levels and metabolic detoxification enzymes activities changes induced by Cd and Cr in Oxya chinensis, discussed toxicological effects of heavy metal and provide basic information as the heavy metal pollution biomarkers of Oxya chinensis. |
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