Isolation And Identification Of Rhizobacteria Producing1-aminocyclopropane-1-carboxylate Deaminase And Inoculation Effects On Wheat Ethylene Metabolism And Growth Under Drought Stress

Plant growth promoting rhizobacteria is one of the most important biotic means toimprove plant drought tolerance by regulate ethylene metabolism. PGPR producing ACC-deaminase were used in this article to inoculate wheat under different levels of drought. Thenthe impact of PGPR on wheat growth, ethylene metabolism and drought tolerance wasresearched and analyzed.1. Six strains of PGPR containing1-aminocyclopropane-1-carboxylate(ACC) deaminase,marked as AL, BL, CL1, CL2, DL, and DS, were isolated from rhizosphere soil of wheat(Triticum aestivum L.) growing in dry land. The activities of ACC deaminase from thesestrains were0.0364,0.0283,0.0651,0.0682,0.0774, and0.0184U/mg protein, respectively.The six strains can also produce indole-3-aceticacid (IAA) and siderophores as well asorganic acids dissolving inorganic phosphate.2. Based on the physiological and biochemical characteristics, morphological featuresand16S rDNA analysis, the strain AL, BL, CL1, CL2, DL, and DS were identified asEnterobacter mori, Enterobacter asburiae, Klebsiella pneumonia, Enterobacter ludwigii,Enterobacter asburiae and Leclercia adecarboxylata.3. Seeds of wheat (Triticum aestivum L.) were inoculated using the six stains of bacteriaproducing high active ACC deaminase. Two weeks after sowing, wheat seedlings wereexposed to different soil water contents: non-limited water condition, medium drought, andsevere drought, corresponding to soil water contents between75%±5%,50%±5%and35%±5%of field water capacity (n=6for each treatment) for six weeks, respectively.Effects of the inoculations on wheat growth, N/P contents, ethylene metabolism and toleranceto drought were investigated. Results showed,(1) Inoculated with six bacteria containing ACC-deaminase can improve the total Ncontent and biomass of wheat under non-limited condition and medium drought, but notimprove them under severe drought. The total P content of wheat leaves and roots was muchthe same in all treatments. (2) In ethylene metabolism, inoculations can reduce the ACC content, ethylene releaseand ACC-oxidase activity evidently in three different treatments of water content. The ACCsynthetase activity of wheat under medium and severe drought was higher than under non-limited water condition, but inoculation of bacteria cannot affect the activity.(3) Besides all, the tolerance to drought of inoculation wheats under medium drought washigher than no-inoculation group, like the higher activity of superoxide dismutase (SOD),hydrogen peroxidase (CAT) and peroxidase (POD), higher soluble protein content and thelower malonic dialdehyde (MDA) content.In conclusion, there are many kinds of PGPR producing high activity ACC-deaminase inrhizosphere soil of wheat growth in dry land; Although inoculation with six PGPR cannotimprove wheat growth under severe drought powerfully, the bacteria containing ACC-deaminase can promote wheat growth under non-limited water condtions and mediumdrought by absorb ACC from roots, produce auxin and increase soil nutrition.