Function of polyamines in growth regulation of rhizobia in host and rhizosphere

1.大豆植株根瘤中积累了大量的腐胺和亚精胺，能够抑制大豆根瘤菌的生长。2.从大豆根中分离到另一种抑制大豆根瘤菌生长的物质，鉴定为4，7-二羟基异黄酮，代谢素。3)亚精胺的抑制作用与亚精胺氧化脱氨基生成的H_2O_2有关。1)细菌对H_2O_2敏感。2)过氧化氢酶的加入抑制了亚精胺的生长抑制。3)许多品系对H_2O_2和亚精胺的耐受性有关。4)日本菜豆的亚精胺抗性突变体获得了对H_2O_2抑制效应的抗性。亚精胺参与了硝酸盐对根瘤固氮活性的抑制作用。5.从大豆幼苗根中分离纯化了胺氧化酶。该酶被归类为I型胺氧化酶。利用纯化的酶进行的实验表明，类菌体表面的胺氧化酶催化氧化脱胺或多胺反应，产生的H_2O_2对类菌体的生长有抑制作用。6.虽然菌体匀浆中含有足够的胺氧化酶和多胺来抑制类菌体的生长，但在培养过程中，根瘤匀浆中的细菌密度并没有下降。

1.Soybean plants accumulated sufficient putrescine and spermidine in their nodules to inhibit the growth of Bradyrhizobium japonicum.2.Another substance that inhibits the growth of B.japonicum strains was isolated from soybean roots, and was identified as 4,7-dihydroxyisoflavone, daizein. The growth inhibition of bacteroids by daizein was depressed by spermidine.3.The following results suggest that H_2O_2 derived from the oxidative deamination of spermidine is responsible for the inhibitory effect of spermidine.1) Bacterois were sensitive to H_2O_2.2) The addition of catalase depressed the growth inhibition of spermidine.3) There was a correlation between the tolerances to H_2O_2 and spermidine in many B.japonicum strains.4) Spermidine resistant mutants of B.japonicum gained resistance to the inhibitory efrect of H_2O_2.4.The results in this study suggest that spermidine is concerned in the inhibition of nitrogen fixation activity of nodules by nitrate.5.Amine oxidase was purified from soybean seedling roots. This enzyme was classified into the type I amine oxidase. The experiments using this purified enzyme suggest that amine oxidase located on the surface of bacteroids catalyzes the oxidative deamination or polyamines, and the produced H_2O_2 cases the growth inhibition of bacteroids.6.Bacterial density in the homogenate of nodules did not decrease during the incubation of the homogenate, although there was enough amine oxidase and polyamines in the homogenate to inhibit the growth of bacteroids.The results obtained in this study suggest a mechanism regulating amine oxidase activity to control the density of bacteroids in the host plant.