盐胁迫下粪产碱菌在水稻根表的定殖和异源固氮基因的表达

异源nif LacZ融合基因在粪产碱菌A15 6 1中的表达活性随盐浓度增加而升高 ,然后逐渐降低 ,nifH LacZ融合基因可以正常表达的盐浓度在 0 .1%～0 .5 %之间 ,盐浓度为 0 .0 5 %时活性最高。A15 6 1在盐浓度为 0 .0 6 %时趋化能力最强 ,随着盐浓度的提高逐渐下降 ,当盐浓度为 3 .0 %时完全丧失趋化能力。一定的盐浓度 (0 .5 % )对固氮粪产碱菌的根表定殖有促进作用 ,该条件下根表定殖的菌体数远大于对照。 3种nif LacZ融合基因在根内的表达部位有显著差异。nifH的表达部位主要分布于根的皮层薄壁组织细胞间隙 ,在条件适宜 (无铵和微量氧 )的部位或某些特殊位置如侧根伸出部位高水平表达。盐胁迫下水稻 耐盐粪产碱菌A15 6 1的联合固氮效率明显高于A15 6 1纯培养物

Expression of Heterologous nif lacZ Genes Fusion in Alcaligenes faecalis Conjugates and Their Colonization of Rice Roots Under Salt Stress

A sharp increase in expression of heterologous nif lacZ gene fusion in A. faecalis A1561was followed by a gradual decrease in expression with the increase in salt concentration. The nifH lacZ gene fusion was expressed at high level when salt concentration was lower than 0.5% . The optimal salt concentrations of NaCl was 0.05% for maximum expression of nifH , 1.0 % for nifA and 0.6% for nifL . A1561 showed high motility and possessed normal flagella under NaCl concentrations from 0.02% to 2.0%. Flagella of bacteria dropped off gradually when salt concentration was higher than 2.8%. The chemotactic value reached its maximum when the cultural medium contained 0.06% NaCl. Chemotaxis of A1561 was repressed totally in the presence of 3% NaCl. A1561 showed a close association with rice roots in the presence of 0.5 % NaCl. The simulation to bacterial colonizing on rice roots surface was obvious under the salt stress of 0.5% NaCl. The number of colonized bacteria was higher under salt stress of 0.5% NaCl than under the 0.05% NaCl. But a number of colonized bacteria on the rice roots surface decrease sharply in the presence of ammonia. The heterologous nifH, nifA and nifL lacZ gene fusion could express well on the surface or in endo rhizosphere of rice roots under salt stress. But the sites and activities of expression of those nif genes fusion inside rice roots tissues were quiet different. The heterologous nifH lacZ gene fusion in A1561 expressed at high level mainly in parenchyma, intercellular space of endodermis or lateral root primordia. Nitrogen fixing activities of A1561 associated with rice seedlings was much higher than that of pure culture of A1561 under salt stress.