Isolation Of 1-aminocyclopropane-1-carboxylic Acid (ACC) Deaminase-containing Plant Growth-promoting Rhizobacteria (PGPR) And Enhancement Of Stress Resistance In Plant

Isolation and identification of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing plant growth-promoting rhizobacteria (PGPR), and enhancement of resistance to salt, drought, flooding and petroleum stress in plants were studied, which layed a foundation for phytoremediation of oil-contaminated coastal zone, and served as an environmentally-friendly and economical alternative to the enhancement of crop production in increasingly saline, dry, inudant and oil-contaminated soils.Four strains of ACC deaminase-containing PGPR were isolated from the oil-contaminated rhizosphere soils of Suaeda heteroptera Kitag, a kind of salty plant, based on the ability to utilize ACC as a sole nitrogen source. These four isolates were identified as Pseudomonas sp. S1, Citrobacter sp. S2, Enterobacter sp. S3 and Klebsiella sp. S4 by 16s rDNA sequence analysis.The results from the growth curve showed that these four bacterial isolates unequally grew in DF salts minimal medium with ACC at 0-3% NaCl or pH 7.5-8.5, among of which, Pseudomonas sp. S1 had the highest ACC deaminase activity. The growth of the bacterial isolates was in agreement with their ACC deaminase activity. ACC deaminase activity of the bacterial isolates was inhibited at either 3% NaCl or pH 8.5.The results from either gnotobiotic growth pouch assay or unsterilized soil pot trial showed that these four bacterial isolates unequally enhanced resistance to salt stress in oat(Avena saliva) or annual ryegrass(Lolium multiflorum) seedlings. Among these four bacterial isolates, S1 was the most effective. Compared with control (no NaCl), more plant growth promotion was observed under 10 g/kg NaCl stress. The greatly significant positive correlations between ACC deaminase activity and plant growth parameters tested were observed by Pearson correlation analysis. The results also showed that ACC deaminase, not indole-3-acetic acid (IAA), may be the primary factor for plant growth promotion. Inoculation with either one or two of three PGPR (S1, S3 and Pseudomonas putida UW4) significantly enhanced resistance to salt, drought and flooding stress in Suaeda heteroptera Kitag. Compared with inoculation with two PGPR, inoculation with single PGPR more significantly enhanced Suaeda heteroptera Kitag salt-resistance. But inoculation with S1 showed no significant difference from inoculation with two PGPR on the enhancement of either drought or flooding resistance in Suaeda heteroptera Kitag.Deleterious effects of salt, flooding and petroleum stress on the roots were more than those on the aboveground parts of either oat or annual ryegrass. But inoculation with S1 significantly enhanced plant stress resistance, and greatly enhanced total petroleum hydrocarbons (TPH) removal efficiency from the rhizosphere soils of either oat or annual ryegrass. The results from the stress kinetics showed that change trend of Fv/Fm, the quantum efficiency of open photosystemâ…¡, was in agreement with that of aboveground length, which may imply that Fv/Fm may be used as a dynamic diagnostic index for enhancement of stress resistance in plant inoculated with PGPR.