载有苜蓿根瘤菌巨型质粒的豇豆根瘤菌侵染苜蓿根瘟的形态

Morphology of Alfalfa Nodules Infectedby Rhizobium sp. Strain Containing A R. meliloti Megaplasmid

生物固氮的过程是把大气氮素还原为氨,为植物生长提供有效的氮素营养。在共生固氮过程中,根瘤菌与豆科植物共生有着较为严格的宿主专性关系,如苜蓿根瘤菌只诱导苜蓿植物结瘤固氮,豌豆根瘤菌只诱导豌豆植物结瘤固氮。

Cowpea Rhizo biu m strain ANU280 containing a symbiotic megaplasmid originated from R. meliloti was found capable of forming nodulelike structures on alfalfa except the infection on its own host of siratro. These nodules are different from those effective nodules induced by R. meliloti. They were smaller and dispersed on lateral roots (see Plate 1-A). The nodule structures were largely composed of meristematic cells with a smaller symbiotic one (see Plate J-E), No dules were ineffective, contained elongated bacteroids within the host cells (see Plate Ⅱ-A2, A3, A4), but the bacteroids quickly senesced and were degraded. Studies with the constructs of Rm nifAp, Rm P1 and Rm P2 by promoterless LacZ gene fusion showed that Rra nifA gene, which were not expressed in the heterologous Rhizobium strain ANU280, might be responsible for the abnormal morphology of alfalfa nodules.