Enhancing The Atrazine Tolerance Of Pennisetum Americanum(L.)K.Schum By Inoculating With Indole-3-acetic Acid Producing Strain Pseudomonas Chlororaphis PAS18

Atrazine is a herbicide widely used in the black soil region of northeast China.Because of its biotoxicity and long environmental residue,it poses a great threat to the ecological environment and attracts widespread attention.Pennisetum with certain tolerance of atrazine has been proved to be a remediation plant that can be applied to atrazine pollution treatment,effectively improving the tolerance of atrazine to atrazine helps to strengthen the atrazine restoration of contaminated plants in terrazine.PGPR can enhance the plant's ability to resist various abiotic stresses,but it is not clear whether PGPR can enhance the tolerance of Pennisetum to atrazine and related mechanisms.Therefore,this study focuses on the response of PGPR-Pseudomonas chlororaphis PAS18 to the regulation of Pennisetum seedling growth,light and parameters,antioxidant enzyme activity and root ion flux to atrazine stress.The grass resistance to atrazine stress and related mechanisms are summarized as follows:?1?The experiment investigated the effects of plant growth promoter PAS18 on the growth of Pennisetum under different concentrations of atrazine.The results showed that the addition of strain PAS18 had a certain promoting effect on the growth of Pennisetum seedlings;it could significantly alleviate the inhibition of 20 mg·kg^-1 atrazine on the growth of Pennisetum seedlings and the production of photosynthetic pigments.With the increase of the bacterial liquid dosage(3.6×10⁷CFU·g^-1,5.4×10⁷ CFU·g^-1,7.2×10⁷ CFU·g^-1,1.08×10⁸ CFU·g^-1,2.16×10⁸ CFU·g^-1),the biomass increased by 50.87%,116.07%,25.21%,6.09%,11.74%compared with the non-bacterial liquid treatment group,chlorophyll content increased by 25.22%,58.26%,18.7%,6.09%,30.43%.The above research results indicate that when the dosage of strain PAS18 is 15 m L(5.4×10⁷ CFU·g^-1 dry soil),the effect of atrazine on alleviating the growth stress of Pennisetum is the most obvious.?2?On this basis,the regulation of the addition of the strain PAS18(5.4×10 ⁷ CFU·g^-1 dry soil)to the accumulation of atrazine and photosynthesis in Pennisetum under different stress conditions were measuring.Under the above inoculation conditions,the strain PAS18 can reduce the atrazine accumulation in Pennisetum in low-level(20 mg·kg^-1)atrazine exposure conditions by 29.71%compared with the non-inoculation treatment.At the same time,the transpiration rate was increased by 27.14%compared with the non-inoculated treatment,and the net photosynthetic rate,stomatal conductance and water utilization rate are increased by 40.42%,58.39%,and 10.79%,respectively.In addition,under the above-mentioned low-level atrazine exposure conditions,the photosynthetic parameters of the inoculation treatment showed no significant difference compared with the non-polluting blank treatment,in which the transpiration rate and net photosynthesis rate of the inoculation treatment group were only reduced by 13.87%,11.04%,and the stomatal conductance and water use efficiency increased by 2.37%and 4.76%,respectively.However,when the exposure level of atrazine is 100 mg·kg^-1,the strain PAS18 alleviates the effect of atrazine on regulating the growth inhibition of Pennisetum.The above results indicate that the strain PAS18(5.4×107 CFU·g^-1 dry soil)can effectively relieve the stress of 20 mg·kg^-1 atrazine on the growth and photosynthesis of Pennisetum seedlings.?3?Physiological analysis showed that atrazine at 20 mg·kg^-1 can cause ROS accumulation in Pennisetum seedlings.Inoculation of strain PAS18(5.4×107 CFU·g^-1 dry soil)can increase the activity of SOD,POD,and CAT in Pennisetum under the exposure level of 20 mg·kg^-1 atrazine compared with the control group by 30.98%,27.00%,36.02%;at the same time under the above inoculation and stress level conditions,the content of O^2·-and H₂O₂ in Pennisetum was reduced by44.90%and 13.40%respectively,and the MDA content was reduced by 44.62%.On the contrary,the regulation effect of the strain PAS18 on antioxidant enzyme activity,free radical and MDA content in Pennisetum chinensis at 100 mg·kg^-1 atrazine stress level was not significantly changed compared with the non-inoculated treatment.The above results indicate that the strain PAS18 can activate the Pennisetum antioxidant enzyme system to eliminate the stress of 20 mg·kg^-1 atrazine on Pennisetum,thereby enhancing the resistance of the tested plants to atrazine.?4?In the later experiment,tissue culture method was adopted,and non-damage micro-measurement technology was used to replace the plant growth promoter PAS18 with indoleacetic acid.The impact of quantitative changes.The results showed that IAA regulated calcium flux under atrazine stress,and the inflow rate decreased from 175 pmolcm^-2·s^-1 to 75 pmolcm^-2·s^-1,with a decrease of up to 57.1%.At the same time,IAA reduced the hydrogen ion flux by 61%,effectively alleviating the Ca²⁺and H⁺absorption state of the test plant roots caused by atrazine stress.Therefore,the strain PAS18 can regulate the defense capacity of antioxidants by maintaining the flux of Ca²⁺and H⁺,and maintain the cell p H balance to reduce the stress of 20 mg·kg^-1 atrazine on Pennisetum.