The Efficiency Of Phrene Degrading Endophytic Bacteria Strain PW7 Colonaziting In Wheat And Its Preliminary Mechanism

At present,organic pollution in soil has become a global environmental problem.Polycyclic aromatic hydrocarbons(PAHs)are a class of common persistent organic pollutants in the environment,and can be absorbed and accumulated in plants and translocated into shoots,which is a major pathway for them to reach the food chain,thereby posing serious threats to animal and human health.As the society pays more attention to the safety problems of agricultural products,it is essential to reduce PAHs contamination in the plants.Endophytic bacteria can promote crop yield,improve stress resistance of plant,reduce plant diseases and insect pests and other physiological functions,and can be used as an important carrier of exogenous genes and biocontrol bacteria.However,whether endophytic bacteria with plant could be used to mediate the uptake and biodegradation of PAHs in plants.This issue is hitherto still under elucidation.This study used an efficient pyrene-degrading endophytic bacterium PW7 which was isolated and stored in the laboratory.Firstly,experiment analysed the antibiotic-resistance of stain PW7 and activities of catechol-2,3-dioxy genase(C230).Then,the influences of strain PW7 colonization on plant growth,phenanthrene uptake,accumulation and metabolization were investigated using greenhouse experiments.Finally,the influences of strain PW7 colonization on enzyme activities and metallothionein of wheat were investigated and its related with metabolism of PAHs in wheat.The theoretical basis of this study will be benefit for reducing the plant PAHs pollution levels and protecting agricultural products against PAHs contamination.The main results were shown as follows:1.Colonization of endophytic bacteria strain PW7 in wheat(1)This study researched the performance of different methods of colonization in plant(control,CK;Irrigate root,IR;soak seed,SS;paint leaf,PL)for reducing the pollution of pyrene in the plant.Endophytic bacteria strain PW7 could be successfully colonized in the wheat and it could be transferred from the root to the shoot.Inoculating wheat with strain PW7 can promote the growth of the wheat and the promotion of wheat with IR is strongest.The wheat can be absorbed pyrene of the soil,and conducted by the roots to shoots.Inoculating wheat with strain PW7 could reduce the pyrene concentration in soil,the order of the concentrations of pyrene in soil from the low to high was IR<SS<PL<CK.With the extension of exposure time,the concentrations of pyrene in soil and the rate of pyrene removal decreased gradually.Inoculating wheat plants with strain PW7 by IR,SS,PL could increase the rate of pyrene removal,the rate of pyrene removal with IR was up to 62.42%,PL was the worst.(2)Colonizing wheat plants with strain PW7 by SS,IR or PL revealed that strain PW7 can reduce the concentrations and accumulation of pyrene in wheat.In comparison with CK,inoculating wheat with strain PW7 reduced the concentrations and accumulation of pyrene in wheat,and it was indicated that strains PW7 colonized into wheat can promote the absorption and metabolism of the pyrene.With the extension of time,the concentrations and accumulation of pyrene in wheat decreased gradually.As the same time and concentration of pollution,the concentrations and accumulation of pyrene were different,the order was IR<SS<PL<CK.Compared with the control reduction rate was IR>SS>PL,the concentrations and accumulation of pyrene of the wheat with IR were the lowest.(3)Colonizing wheat with strain PW7 by IR,SS or PL revealed that strain PW7 can reduce the transmission factors and concentration factors.With increasing pyrene concentrations and the extension of exposure time,the transmission factors and concentration factors decreased gradually.Colonized in different methods,the concentration factors of the wheat was IR<SS<PL<CK,the transmission factors of the wheat was IR<PL<SS<CK.Wheat root for the concentration factors and transmission factors of pyrene is far greater than the shoot.It was supposed that most pyrene was degraded in the roots,and the rate of pyrene removal in soil and the wheat was IR>SS>PL.Our results indicated that inoculation of strain PW7 in wheat could reduce the pyrene contamination in wheat.Among three ways of inoculation in this test,the way of irrigate root was the best way for reducing concentrations of pyrene for plants.2.Colonization of endophytic bacteria strain PW7 in wheat influences on enzyme activities of wheat(1)Catechol-2,3-dioxy genase(C230)is key to degrade pyrene in endophytic bacteria.Colonizing wheat with strain PW7 by IR,SS or PL revealed that strain PW7 can strengthen the activities of C230 in wheat and the activities of C230 in root is greater than the shoot.As the same concentration of pollution,the activities of C230 in the shoot was IR>PL>SS,the activities of C230 in the root was IR>SS>PL.As the same methods of colonization,the activities of C230 in the root and shoot was 50mg/kg>100mg/kg>0mg/kg.In a certain concentration range,the strain PW7 colonized in wheat could produced C230 and promote the degradation of pyrene with the stress of pyrene.(2)Inoculating wheat with strain PW7 influenced the activities of peroxidase(POD)and poly phenol oxidase(PPO)in plants.The activities of POD and PPO in shoots compared with these in roots,the activities of POD and PPO in roots is far greater than these in shoots.As the same concentration of pollution,colonized in different methods,the activities of POD and PPO in shoots were different,the order was IR<PL<SS<CK,and the activities of POD and PPO in roots was IR>SS>PL>CK.The method of irrigate root was the best way for promoting activities of enzymes about degrading pyrene in plants.(3)The stress of pyrene had a significant effect on the content of metallothionein(MT),and it can also induce the plant's own defense to remove hydroxyl radical.As the same methods of colonization,the activities of MT in roots was the highest when the concentration of pyrene is 50mg/kg,and the activities of MT in shoots was 0mg/kg>50mg/kg>100mg/kg.It was supposed that pyrene could increase the activities of MT in the wheats in a certain concentration range.But when pyrene exceeded a certain concentration range,it would restrain the activities of MT in the wheats and produce toxic effects on wheats and strains.As the same concentration of pollution,the activities of MT in shoots and roots was IR>SS>PL>CK.Our results indicated the strain PW7 colonized in wheat could effectively induce the production of the MT and the effect was the best by irrigate root.