Cermola M, Fedorova E, Taté R, Riccio A, Favre R, Patriarca E J
International Institute of Genetics and Biophysics, CNR, Naples, Italy.
Mol Plant Microbe Interact. 2000 Jul;13(7):733-41. doi: 10.1094/MPMI.2000.13.7.733.
By means of a detailed ultrastructural analysis of nodules induced by Rhizobium etli on the roots of Phaseolus vulgaris, we observe that the development of host-invaded cells is not synchronous. An accumulation of mitochondria was found in freshly invaded host cells, containing only a few symbiosomes (SBs) that are released from highly branched intracellular ramification of the infection threads. Moreover, besides the fusion between the SB membrane with host secretory vesicles, we observe also a great number of fusions between the outer leaflets of adjoining SB membranes, thus resulting in structures that resemble the tight junction network (zona occludens with a five-layered structure) of epithelian cells. This process was found to be induced strongly and earlier both in the invaded host cells of ineffective nodules (elicited by Fix- mutant strains of R. etli) and in the older (senescence) invaded cells of effective nodules, whereas bacteroid division is seldom if ever observed. Our observations strongly suggest that multiple-occupancy SBs also arise by fusion of single-occupancy SBs and the physiological consequence of this process is discussed.
通过对菜豆根上由菜豆根瘤菌诱导形成的根瘤进行详细的超微结构分析，我们观察到宿主细胞的发育并不同步。在刚被侵染的宿主细胞中发现线粒体聚集，这些细胞仅含有少量共生体（SBs），它们从感染丝高度分支的细胞内分支中释放出来。此外，除了SB膜与宿主分泌囊泡之间的融合外，我们还观察到相邻SB膜外小叶之间大量的融合，从而形成类似于上皮细胞紧密连接网络（具有五层结构的闭锁小带）的结构。这一过程在无效根瘤（由菜豆根瘤菌的Fix-突变菌株引发）的被侵染宿主细胞以及有效根瘤的较老（衰老）被侵染细胞中均被强烈且较早地诱导，而类菌体分裂很少被观察到，甚至从未被观察到。我们的观察结果强烈表明，多占据的SBs也通过单占据SBs的融合产生，并讨论了这一过程的生理后果。
