Screening Of Plant Growth Promoting Bacteria Under Saline-alkali Stress And Its Growth Promoting Mechanism

Soil salinization is a serious threat to the benign cycle of ecological environment and the sound development of agriculture and animal husbandry.The development of microbial fertilizer provides a new direction for harnessing saline-alkali land.In this study,99 strains with growth promoting potential were screened from more than 400 rhizosphere microorganisms isolated by our group from the plants grown in saline-alkali soil.According to 16S rDNA sequencing results,the plant growth promoting rhizobacteria(PGPR)were classified into 15 genera,including Enterobacter,Bacillus and Acinetobacter as well.Among these,the enterobacter bacteria,AD2-2,had the most obvious effect of plant growth-promoting.Therefore,AD2-2 was used for further analysis of growth-promoting theorization and plant response mechanism.The results are as below:1.AD2-2 has strong saline-alkali--resistance.It can secrete H+to decrease pH of rhizosphere to promote root growth under saline-alkali condition.AD2-2 can secret IAA to affect plant endogenous auxin level;and ACC deaminase to remove the inhibition of ethylene on plant growth.AD2-2 also had the ability to synthesize ferritin to supply absorbable iron ion for plants.AD2-2 was also able to convert insoluble phosphorus into soluble phosphate to promote plant phosphate absorbance.2.The Enterobacteriaceae bacteria AD2-2 significantly promoted growth and development of Arabidopsis,rice and maize under saline-alkali condition.Not only the primary root length became significantly longer,but also the lateral roots and root hairs became longer and denser3.Observation of the expression levels of auxin reporter genes DR5::GUS and DR5::GFP revealed that AD2-2 affected the endogenous auxin level in root tips under normal condition and saline-alkali stress.4.AD2-2 improved length of root apical meristem(RAM)since.it promoted cell division in RAM zone which resulted increased cell number.5.AD2-2 promoted the development of the border cells,resulting in increased layers of border cells at root tip which make the border cells easy to fall off.The fallen border cells can recruit PGPR and provide nutrients for PGPR.Our results indicated that under saline-alkali stress,AD2-2 promotes plant growth via various mechanisms.The plants not only receive help from PGPR,but also recruit PGPR and provide nutrition for PGPR.A real interaction between plants and PGPR is achieved.This study provides clues for the selection and development of salt-alkali-resistant probiotics.