Effects Of Endophytes Colonization On Degradation Of Chlorpyrifos And Phytotoxicity In Rice

Chlorpyrifos is a kind of organophosphorus insecticide widely used in agricultural production.It is mainly used to control rice planthopper,rice leaf rolling borer,borer and other pests in rice fields.Chlorpyrifos residues in the environment have a certain influence on human health through the enrichment of the biological chain.In this study,three strains of endophytic bacteria with chlorpyrifos degradation characteristics were isolated from rice with chronic chlorpyrifos contamination,and then these endophytes were colonized into rice,respectively,to study their effects on the growth of rice and the degradation of chlorpyrifos,and to preliminarily analyze the mechanism of its synergistic degradation of chlorpyrifos in rice.The main contents are as follows:1.Three strains of endophytic bacteria with chlorpyrifos degradation characteristics were isolated from rice exposed to chronic chlorpyrifos contamination and they were named DJ-1,DJ-2,and DJ-3.The three strains could grow in mineral salt medium with chlorpyrifos as the sole carbon source.The extraction and detection methods of chlorpyrifos in mineral salt medium were established.The 15 days degradation rates of chlorpyrifos by DJ-1,DJ-2 and DJ-3 reached 16.94 %,21.60 % and 19.32 %respectively.With the degradation rate of chlorpyrifos as the research object,and taking the culture temperature,p H and concentration of chlorpyrifos as independent variables,the central combination response surface methodology was used to optimize the degradation conditions of these three endophytic strains in vitro.2.The green fluorescent protein gene was successfully introduced into the three strains of DJ-1,DJ-2 and DJ-3 by three-parent hybridization method,and the three strains with green fluorescent protein were colonized into the three-leaf stagerice by soaking the root,and the distribution of the three strains in different tissues of rice was observed by laser confocal microscope.Colonization dynamics of three endophytic strains in rice were calculated by antibiotic labeling method.Rice colonized by DJ-1,DJ-2 and DJ-3 could significantly promote the growth of rice plants under chlorpyrifos stress,and the fresh weight of rice colonized by endophytic bacteria increased by44.28%-64.66% compared with the control group.Colonization of rice by DJ-1,DJ-2and DJ-3 also promoted the degradation of chlorpyrifos in rice,and the half-life of chlropyrifos in rice colonized by endophytic bacteria was shortened by 0.5 d-1.0 d.3.The three strains DJ-1,DJ-2 and DJ-3 can produce indole acetic acid(IAA)and siderophores,have aminocyclopropanicarboxylic acid(ACC)deaminase activity and have phosphorus solubility,which can promote the rapid growth of rice and enhance the degradation ability of chlorpyrifos in rice.After chlorpyrifos treatment,the content of cytochrome P450 in rice increased significantly,the activity of carboxyliase was inhibited,while the activity of glutathione S-transferase did not change significantly.Compared with the control group,the content of cytochrome P450 and the activity of carboxylipase did not change significantly after the colonization of rice by the endophytic bacteria DJ-1,DJ-2 and DJ-3,but the activity of glutathione S-transferase increased significantly.It was speculated that endophytic bacteria could promote the degradation of chlorpyrifos in rice by promoting the growth of rice and enhancing the activity of glutathione S-transferase in rice.