Figure 10.

Ultrastructure of wild-type (A) and rosR mutant infection threads (B,C). Abbreviations: IT, infection thread; TM, thread matrix; B, bacteria; D, dictyosome; ER, endoplasmic reticulum; short black arrow, thread wall; long black arrows, deposits of more translucent material between osmophilic layers of the thread wall; white long arrows, short ER cisterns in close contact with the thread membrane; short white arrows, transport vesicles. Bar = 5 μm. (D,E) Infection droplets containing rosR mutant bacteria. (D) A lateral infection droplet on an infection thread. (E) A large infection droplet inside the host cell. B, bacteria; ID, droplet; IT infection thread; N, nucleus; black triangle, degenerated bacteroids; black arrow heads, vesicles separated from the thread membrane surrounding the infection droplet. Bar = 2 μm for (D) and 5 μm for (E). (F) Symbiosomes containing rosR mutant bacteroids in the young infected host cell; note three types of bacteroids present: BA, bacteroids similar to those observed in the early symbiosis zone of wild-type nodules; double triangle, differentiating bacteroids; triangle, degenerated bacteroids. Bar = 5 μm. (G) A mature infected host cell: S, starch grain; rosette, abnormally differentiated rosR mutant bacteroids; black arrows, lytic compartments with degrading bacteroids. Bar = 5 μm. (H) Symbiosomes containing wild-type bacteroids in a mature infected host cell: BA, normal bacteroids. Bar = 5 μm. H₂O₂ detection in Rt24.2 and Rt2472 nodules as electron-dense precipitates formed in the presence of cerium chloride (I–L). H₂O₂ localization in the cell wall of a wild-type infection thread (I,J). H₂O₂ precipitates (white arrows) present in the cell wall of the infection threads containing rosR mutant bacteria and on the surface of bacteroids and their peribacteroidal membranes (K,L). Bar = 2.5 μm (for I,J), Bar = 5 μm (for K,L).