| With the rapid growth of world population, the food crisis has become the focus of attention.International Rice Research Institute pointed out that increase of rice yeild is the key to solve this impending crisis, as for now, China where rice is the staple crops, Application of industrial chemical fertilizers and pesticides containing heavy materials had been considered as the main way to achieve the goal, which caused changes in the physical and chemical properties of soil, and led to decrease in crop production, and even affected the crop quality and safety, finally did harm to human health. The endophytic bacteria were gradually proved to be an alternative bio-ecological resources to prevent the deterioration of this phenomenon, For the purpose of revealing the colonization and growth promotion properties by this endophytic bacteria in rice, the following experiments were conducted.18 nitrogen-fixing bacterial strains and 11 phosphate-solubilizing bacterial strains were isolated from surface sterilized roots, stems and leaves of wild rice.On the basis of rescreening experiments,physiological and biochemical tests and 16S rDNA sequence analysis,three endphytic bacteria were confirmed which were Klebsiella strain HAUM12,Enterobacter strain HAUM3 and Pantoea agglomerans strain HAUM1. By cellulose and pectin degradation test, HAUM1 showed better of infection capability than the other two strains. Results of pot experiment indicated that the rice inoculated with HAUM1 were significantly higher than the other treatments at 15 day after inoculation.In conclusion, HAUM1 was chosen as the reseach strain.HAUM1 was gfp marked by bacterial conjugation experiment. The conjugant which appeared stable in resistance and fluorescence intensity after 15 generation was picked out for a gfp gene amplification,then the positive one was selected for the futher study. Combining the use of LSCM with plating experiment, to examine infection,dissemination and colonization of host rice by gfp-tagged strain HAUM1,Results indicated that the symplasmata structure formed by hundreds of bacterial showed up at the beginning of infection process in roots at 3 day, at 5 day these symplasmatas gradually decentralized and bacteria started to colonize the cells and intercell spaces of cortex tissues, a large number of bacteria migrated into stems at 7 day and then colonized leaves at 15 day.To reveal the influence by strain HAUM1 on host, the rice seedlings were respectively inoculated with HAUM1 and other two phosphate- solubilizing bacterial PA10(Agrobacterium sp.) and P11(Pantoea agglomerans), HAUM1 was proved possessing the most significant increase almost in all aspects of biomass and accumulating the highest levels of phosphate and cytochrome(a+b). It was also detected to produce indole-3-acetic acid and abscisic acid as high as 23.9mg/L and 38.5mg/L by HPLC test.Results indicated that strain HAUM1 had built an eompatibassociation with host plant, and this growth-promoting influcence was partly due to its phosphate-solubilizing,photosynthesis activity and auxin productivity as well.Considered collectively,all the findings suggested that this kind of endophytic plant-growth-promoting bacteria are far more inclusive and dynamic than we thought therefore enhancing the study in this field holds a promising potential for a long term of sustainable rural economy. |
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