Root Colonization of Sinorhizobium fredii pSym-Cured Strain HN01 in Rhizosphere of Glycine max
消除共生质粒的费氏中华根瘤菌HND29SR在大豆根圈的定殖动态

Root colonization is a first step during the development of symbiosis between rhizobium and legume plant. It was reported that rhizobium colonization on roots was determined by its ability of chemotaxis and mobility. The relationship between indigenous plasmid and root colonization was reported by using luxAB gene marked strains and modified Leonard jar apparatus. The root colonization dynamics of Sinorhizobium fredii HN01, HN01L marked with luxAB and HND29SR (pSym cured HN01) in rhizosphere of Glycine max in sterilized pot sand microcosm was studied. The results showed that the root colonization dynamics of HN01, HN01L and HND29SR was basically identical and their colonization density decreased rapidly first 12 days stage during a single inoculation experiment. The root colonization density of HN01 and HN01L increased gradual up to 6 49log cfu/g root and 6 78 log cfu/g root respectively on the 16th day after inoculation, and reduced again to keep a relative stable level. But the root colonization density of HND29SR decreased constantly at first 16 days and then began to rise up to a relative stable colonization density of 6.94 log cfu/g root until the 35th day. Furthermore, the root colonization dynamics of double inoculation of HN01 tested in soybean rhizosphere shown no significant differences. The result demonstrated that the introduce of mark gene luxAB did not influence colonization ability of HN01 so that marked strain HN01L could be used as referential strain for further studies. The root colonization dynamics of double inoculation of HN01L and HND29SR was also no significant differences. The results indicted that the pSym deletion of HN01 did not affect its root colonization ability in soybean rhizosphere. The results of nodule occupancy detected by using X ray film exposured by luminous nodules proved that the competitive ability of nodulation between HN01 and HN01L was nearly the same which was also corresponded to the results of root colonization. Our results indicated that genes regulating root colonization of rhizobia are not located on the symbiotic plasmid.