Screening ACC Deaminase-containing Bacteria For Relieving Salt Stress And Promoting Growth And Influence On Ion Absorption Of Cotton

Secondary salinization was largely occured in the cotton field of Xinjiang. The work reported here evaluates whether bacteria populating salty environments can confer resistance in cotton to salt stress. Plant growth-promoting bacteria that have ACC deaminase activity were isolated from soil samples taken from the secondary salinization cotton fields of northern Xinjiang.In order to screen PGPRs that confer resistance in cotton to salt stress, the effect of inoculation with different PGPRs isolates on saline-tolerance of cotton were investigated with pot experiment.Through primary screening experiment, Rs-2, Rs-5 and Rs-35 were obtained.These novel bacteria have been identified as Raoultella planticola Rs-2,Klebsiella oxytoca Rs-5 and Enterobacter cloacae Rs-35,GenBank Accession number are EF551363,EF508705,EF508704。Each strain displayed similar levels of ACC deaminase activity,.and confer resistance to salt stress in cotton(Gossypium hirsutum L).The enzyme activity of ACC deaminase were 0.832±0.032U/mg,0.795±0.031U/mg,0.770±0.040U/mg,respectively.Soil inoculations with respective bacterial strains increased the shoot lengths and fresh and dry weights of potted cotton plants under salt stress. The germinating rate and fraction surviving of cotton treated with PGPRs were enhanced 25.9% and 24.8% compared with untreated control,respectively. The average stem length of cotton was increased of 14.6%.The average dry weight of cotton was increased of 31.2%.Scanning Electron Microscopy(SEM) Observations on Root Colonization of Plant Growth-promoting Rhizobacteria in Cotton showed that all of three strains bacteria could bind themselves upon cotton root surface in two different pattern under 0.8% NaCl stress. There was one mainly dispersal pattern of introduced PGPR on the root in which PGPR were carried passively by growing root tip.The changes of endogenesis hormone in leaves and root of cotton inoculated with PGPRs were investigated under salt stress.The results showed that:Rs-2 and Rs-5 could reduce the quantity of Eth and content of endogensis ABA of cotton, Rs-35 could enhance content of endogensis IAA besides reduce the quantity of Eth of cotton. Tissue concentrations of Na,Ca,K,Mg and Fe a by inductively coupled plasma atomicemission spectroscopy was determined to study the effect of NaCl on mineral elements concentration of cotton inoculated with PGPRs. It was found this bacterial strain could also influence the ion accumulation ability of cotton,The content of Na was reduced by the Rs-2,Rs-5 and Rs-35 under salt stress. It was also observed that the contents of K and Ca in the cotton under NaCl stress was increased by the relieving-salt-stress and growth-promoting bacteria.while the ratios of K⁺/Na⁺ and Ca²⁺/Na⁺ were enhanced. relieving-salt-stress and growth-promoting bacteria significantly increased the contents of Fe in cotton.Rs-35 increased the contents of Mg,especially.The adaptive changes in activity of tonoplast H+-ATPase and plasmalemma H⁺-ATPase on different time sampling from the roots and leaves of cotton inoculated with PGPRs under salt stress were studied. It was showed that the activity of V-H+-ATPase and P-H⁺-ATPase of control cotton decreased under salt stress and reached minimum values under thesalt stress for 24h, while the activities .The results also showed that the V-H⁺-ATPase and P-H⁺-ATPase activities of cotton root and leaves system treated by Rs-2 and Rs-5 were increased. The changes in activity of V-H⁺-ATPase and P-H⁺-ATPase of cotton inoculated with Rs-35 on different time was different with that treatment with Rs-2 and Rs-5.We quantified the GhNHX1 gene expression on different time sampling from the roots and leaves of cotton inoculated with PGPRs under salt stress ,which code the Na⁺/H⁺ antiporter protein, by real-time polymerase chain reaction (PCR) assays.Expression of the GhNHX1 gene was higher in leaves and root of cotton inoculated with Rs-2 than CK under salt-stress.Expression of the GhNHX1 gene was increased in cotton leaves, which inoculated with Rs-5 and Rs-35 also.In addinition,We reported the development of specific primers for the cotton(Gossypium hirsutum) (+)-d-cadinene synthase gene and PCR cycling conditions suitalbe for which use as an endogenous reference gene in PCR assays.,this gene could be used as an endogenous reference gene of cotton in practial real time detection.