July
2000
, Volume
13
, Number
7
Pages
733
-
741
Authors
Michele
Cermola
,
Elena
Fedorova
,
Rosarita
Taté
,
Anna
Riccio
,
Renee
Favre
,
and
Eduardo J.
Patriarca
Affiliations
International Institute of Genetics and Biophysics, CNR, Via Marconi 10, 80125 Naples, Italy
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RelatedArticle
Accepted 5 April 2000.
Abstract
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.
JnArticleKeywords
Additional keywords:
nifA,
nitrogenase activity.
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© 2000 The American Phytopathological Society