Journal of Experimental Botany, Vol. 52, No. 364, pp. 2181-2186,
November 1, 2001
© 2001 Oxford University Press
Original Papers |
Redifferentiation of bacteria isolated from Lotus japonicus root nodules colonized by Rhizobium sp. NGR234
Botanical Institute, Hebelstrasse 1, CH-4056 Basel, Switzerland
In most studies concerning legume root nodules, the question to what extent the nodule-borne bacteroids survive nodule senescence has not been properly addressed. At present, there is no ‘model system’ to study these aspects in detail. Such a system with Lotus japonicus and the broad host range Rhizobium sp. NGR234 has been developed. L. japonicus L. cv. Gifu was inoculated with Rhizobium sp. NGR234 and grown over a 12 week time period. The first nodules could be harvested after 3 weeks. Nodulation reached a plateau after 11 weeks with a mean of 64 nodules having a biomass of nearly 100 mg FW per plant. Nodules were harvested and homogenized at different stages of plant development. Microscopic inspection of the extracts revealed that, typically, nodules contained c. 15x109 bacteroids g-1 FW, and that about 60% of the bacteroids were viable as judged by vital staining. When aliquots of the extracts were plated on selective media, a substantial number of ‘colony-forming units’ was observed in all cases, indicating that a considerable fraction of the bacteroids had the potential to redifferentiate into growing bacteria. In nodules from the early developmental stages, the fraction of total bacteroids yielding CFUs amounted to about 20%, or one-third of the bacteroids judged to be viable after extraction, and it increased slightly when the plants started to flower. In order to see how nodule senescence affected the survival and redifferentiation potential of bacteroids, some plants were placed in the dark for 1 week. This led to typical symptoms of senescence in the nodules such as an almost complete loss of nitrogenase activity and a considerable decrease in soluble proteins. However, surprisingly, the number of total and viable bacteroids g-1 nodule FW remained virtually constant, and the fraction of total bacteroids yielding CFUs did not decrease but significantly increased up to 75% of the bacteroids judged to be viable after extraction. This result indicates that during nodule senescence bacteroids might be induced to redifferentiate into the state of free-living, growing bacteria.
Key words: Nitrogen fixation, senescence, symbiosis, vital staining.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  O. Schumpp, M. Crevecoeur, W. J. Broughton, and W. J. Deakin Delayed maturation of nodules reduces symbiotic effectiveness of the Lotus japonicus-Rhizobium sp. NGR234 interaction J. Exp. Bot., February 1, 2009; 60(2): 581 - 590. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Mergaert, T. Uchiumi, B. Alunni, G. Evanno, A. Cheron, O. Catrice, A.-E. Mausset, F. Barloy-Hubler, F. Galibert, A. Kondorosi, et al. Eukaryotic control on bacterial cell cycle and differentiation in the Rhizobium-legume symbiosis PNAS, March 28, 2006; 103(13): 5230 - 5235. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Shibata, H. Mitsui, and H. Kouchi Acetylation of a Fucosyl Residue at the Reducing End of Mesorhizobium loti Nod Factors is Not Essential for Nodulation of Lotus japonicus Plant Cell Physiol., June 1, 2005; 46(6): 1016 - 1020. [Abstract] [Full Text] [PDF]
|
|