Nodule invasion and symbiosome differentiation during Rhizobium etli-Phaseolus vulgaris symbiosis.
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.
Cermola
M
M
International Institute of Genetics and Biophysics, CNR, Naples, Italy.
Fedorova
E
E
Taté
R
R
Riccio
A
A
Favre
R
R
Patriarca
E J
EJ
D002454:Cell Differentiation; D007887:Fabaceae / Q000166:cytology / Q000382:microbiology* / Q000502:physiology*; D009591:Nitrogenase / Q000378:metabolism; D018517:Plant Roots / Q000382:microbiology / Q000502:physiology / Q000648:ultrastructure; D010946:Plants, Medicinal; D012231:Rhizobium / Q000502:physiology*; D013559:Symbiosis
D009591:Nitrogenase