The Physiological Responses Of Maize Seedlings To Five Chemical Insecticides Stress

Nowadays chemical method plays a major role in plant diseases and pests control. Alarge number of insecticides have been found to interfere with plant metabolism. Increasingstudies suggest that insecticides are one of the plant stress elements that affect plant growthand productivity by interfering cell metabolic and biochemical activities. In this paper, wetested the effects of five commonly used insecticides on maize seedling leaves, such asavermectin, emamectin, imidacloprid, deltamethrin and omethoate, in order to provide sometheoretical guidance for the rational use of insecticides, and provide a more scientific basis forthe rational evaluation of ecological security of insecticides.The maize seedlings were planted in air-conditioned growth cabinets, after the seedlingshad three fully expanded leaves, the third young leaf of each seedling was smeared30μmlinsecticides. Measurements were done at the24th hour, after the insecticides were smeared.The commonly used concentration in the production was selected, all of them were dilutedwith acetone to500times,1000times and1500times. The content of chlorophyll, solublesugar, free amino acid, soluble protein and MDA and the activity of the majordefence-enzyme such as superoxide dismutases （SOD）, catalases （CAT）, ascorbateperoxidases （APX）, dehydroascorbate reductase （DHAR） and glutathione reductase （GR）, andconcentrations of ascorbate and glutathione, and the hydrogen peroxide （H₂O₂） productionwas measured. In addition, we also measured the ultrastructural changes of maize seedlingsunder the stress of the omethoate and permethrin. The results are as following:1. After sprayed the five pesticides24hours, the maize seedlings show a significantincrease in proline content, while the free amino acids and soluble protein content decreased,under the imidacloprid stress, corn seedlings chlorophyll and soluble sugar content will rise.2. Avermectin, emamectin, deltamethrin and omethoate treated corn seedlings H₂O₂content, O₂^-content and MDA content were increased significantly, and there was significantdifference with the control, H₂O₂content in maize seedlings and the content of O₂^-increasedafter the treatment of imidacloprid, but MDA content decreased. 3. After24hours, the maize seedlings under five insecticides’ stress, SOD, POD activitywere increased. Under the avermectin and omethoate stress, the APX activity of maizeseedlings decreased; the omethoate will make the GPX activity increased, while GPX activitydecreased after treatment with other four kinds of insecticides.4. Theated with1500times avermectin and deltamethrin, the maize seedlings AsAcontent increased, the five insecticides reduce the maize seedlings’ GSH content. Avermectinand emamectin treated result the the maize seedlings MDHAR and DHAR activities activitydecline, under the stress of imidacloprid, deltamethrin and omethoate, the MDHAR andDHAR activity was increased. The AO activity does not change with regularity. Fiveinsecticides stress will cause the rise of of corn seedlings GR activity.5. Electron microscope studies reveal that topical application of deltamethrin causedplasmolysis of cells of adaxial epidermis, mitochondrial cristae degraded, and loosen arrangedlamella of amyloplasts. While the organophosphorus insecticide omethoate caused directinjury to leaf ultrastructures including cell wall breakdown of abaxial epidermis cells, innercells, and stomata guard cells; degradation of mitochondrial membrane and chloroplastenvelope membrane; and abnormal changes of lamella arrangement of chloroplast. In addition,altered accumulation of peroxisomes and starch grains were observed in response to highconcentration of omethoate.So we speculated that, in this agent concentration, avermectin, emamectin, deltamethrinand omethoate was harm to the corn seedlings, while imidacloprid has ecological security tomaize seedlings.