| Abstract: | Ultrastructural changes of the infected cells have been observed by transmission electron microscopy during pea root nodule senescence. The infected cells and bacteroids of pea nodules ultimately senesce, their senescence has certain laws and features. Firstly, peribacteroid membrane were loosened, leaving a large electron-empty space with fibrillar and vesicular material. Then bacter0id cytoplasm lost features and aggregated into some clustered electron- dense material. At next stage bacteroids were structurally emtpy and appeared like “ghost” cells. Companying bacteroid senescence, host cytoplasm changed from dark to light in electron density and cell organelles gradually decreased. After the host cell tonoplasts and plasmalemma broke down, the infected cells showed a chaotic state of bacteroids and host cell debrises. Finally, infected cells disintegrated completely. Sometimes some young bacteria were seen in the intercellular spaces surrounded by degenerating cells, in the degenerating cytoplasm. A few infection threads were also found among the disintegrated bacteroids, even some of them were releasing the bacteria into the degenerating host cytoplasm. |
