| Popis: |
The infected cells of mature soybean root nodules have no vacuole; instead, the main body of the cell is packed with symbiosomes. Symbiosomes are the basic units of nitrogen fixation, comprising the nitrogen-fixing bacteroids and the surrounding peribacteroid membrane. For efficient passage of nutrients between the bacteroids and the plant, it seems likely that infected cell structure is highly organised with clear diffusion pathways through the cell (i. e. between symbiosomes). We have investigated the cytoskeleton of infected cells using immunocytochemical microscopy. In mature nodules, both cortical and nuclear associated microtubule (MT) arrays were observed in infected cells. The cortical MT’s appeared to occur in bundles and were organised so that strands were roughly parallel and oriented transverse to the long axis of the cell. They did not appear to be associated with symbiosomes. Three different arrays of actin filaments could be distinguished in infected cells: cortical, cytoplasmic and nuclear-associated. The cortical array was limited to a few prominent strands with similar orientation as the microtubules. The nuclear-associated actin array radiated from the nucleus to the cell cortex. The most striking aspect of infected cell actin was the cytoplasmic array which extended throughout the cytoplasm of the cell in a honeycomb structure, probably inserted between and interacting with the symbiosomes. In contrast, uninfected cells had only cortical actin which was oriented randomly. Cells in the nodule primordia (which contain no symbiosomes) had only nuclear associated and cortical actin arrays, the latter in randomly organised, circular patterns. In developing nodules, infected cells showed a cytoplasmic array of actin filaments but it was randomly organised without the distinctive honeycomb structure seen in mature nodule cells. |
