Fredii Gene Markers And Competitive Nodulation

Two plasmids. pHN102 with luxAB and pHN129 with gfp were transferred into Sinorhizobium fredii WWG18 and HNT29 by the method of tri-parental mating. Transconjugants WWG18-/wx and HNT29-g/p were obtained. The results of stability experiments showed that both luxAB and gfp could stablely inherit in marked strains in either free-living or symbiosis conditions by means of light emission detection.The results of competitive nodulation tests between the marked strains showed that the higher colonization density of the marked strain on the roots, the higher the ratio of nodule occupancy and the stronger competitive nodulation ability. The ratio of nodule occupancy of HNT29-g/p is higher than that of WWG18-lux and the ability of competitive nodulation of HNT29-gfp is stronger than that of WWG18-lux that proved the ratio of nodule occupancy was mainly determinated by the strain itself. The ratio of nodule occupancy could be increased according to the cell number of inoculated Sinorhizobium fredii.By using a self-designed split-root-system called Micro-rhizobox, it was demonstrated that the nodulation on one half-side root might suppress subsequent nodule formation on the opposite. Comparing with the results obtained from pot plant experiment using Fahraeus nitrogen-free plant grown solution, the total nodule numbers declined when chemical nitrogen was added. The suppression by different concentrations of (MH4)2SO4 on nodule formation was equal- in two sides, of roots. Suppression on nodule development from another side of a split-root system was enhanced with the increasement of (NH4)2SO4 concentrations When the (NH4)2SO4 concentration was increased to 10mM. the nodule could not be formed.