豇豆根瘤菌NGR234和紫云英根瘤菌109感染紫云英的比较研究

利用光学和电子显微镜对紫云英根瘤菌菌株109和广宿主的快生型根瘤菌菌株NGR234感染温带型豆科植物紫云英进行了研究,结果表明根瘤菌感染紫云英是通过在根毛中形成侵染线的途径。电子显微镜研究揭示了固氮根瘤中细胞内侵染线的存在。接种二天后,首先可观察到根毛的卷曲或分枝。接种四至五天后,在每株植物卷曲的根毛中可看到侵染线。接种八至十天后的植株出现肉眼可见的根瘤。菌株NGR234能够在紫云英上诱导根毛的卷曲,侵染线和根瘤的形成,但所形成的根瘤却未能固氮,根瘤中无明显的类菌体区,但有少数包有细菌的侵染线。NGR234抗抗菌素的衍生菌均未能使紫云英结瘤。将NGR234的共生质粒转移至三叶草、苜蓿、豌豆、快生型大豆根瘤菌和农杆菌,亦未能使这些细菌获得紫云英上结瘤的能力。

INFECTION OF ASTRAGALUS SINICUS BY RHIZOBIUM ASTRAGALUS AND RHIZOBIUM SP STRAIN NGR 234

The infection of the temperate legume Astragalus sinicus by Rhizobium astragalus strain 109 and the broad-host-range, fastgrowing Rhizobium strain NGR 234 was studied using both light and electron microscopy. Rhizobium infection of A. sinicus was shown to be via infection threads formed in root hairs. Electron microscopic studies revealed intra-cellular infection threads in nitrogen-fixing nodules. Root hair curling or branching was first observed 2 days after Rhizobiurn inoculation. Infection threads were seen in curled root hairs on each plant between 4--5 days after inoculation.Nodules were visible on plants 8-10 days after inoculation. Strain NGR234 was able to induce root hair curling and the formation of infection threads and nodules on A. sinicus. However the nodules formed were unable to fix nitrogen. There was no obvious bacteroid zone, but there were few infection threads packed with bacteria in the nodules. The antibitic resistant derivatives of strain NGR 234 failed to nodulate A. sinicus. R. trifolii, R. meliloti, R. leguminosarum, Bradyrhizobium japonicum and Agrobacterium tumefacins strains were unable to infect A. sinicus by the transfer of the Sym-plasmid of strain NGR 234 into these strains.