FIG. 4.

Electron micrographs of nodules harvested 7 days after inoculation with rhizobia. (A) Peas infected with wild-type R. leguminosarum bv. viciae 3841. (B) Peas infected with RU4040 (bacA). (C) Beans infected with wild-type 4292. (D) Beans infected with RU4109 (bacA). Wild-type 3841 shows a mixture of developing and mature bacteroids (A), while for RU4040 the only bacteria we observed were in infection threads (shown), with only a few cells being released into infection droplets (B). Note that there are no mature bacteroids in nodules infected with RU4040, while those inoculated with 3841 are full of them. In contrast, the electron micrographs of wild-type and bacA strains from bean nodules are essentially indistinguishable, with numerous mature bacteroids. Abbreviations: IT, infection thread; ID, infection droplet; Ba, released bacteria; Bd, bacteroid.