scholarly journals Rhizobium meliloti exopolysaccharide Mutants Elicit Feedback Regulation of Nodule Formation in Alfalfa

1990 ◽  
Vol 92 (2) ◽  
pp. 368-374 ◽  
Author(s):  
Gustavo Caetano-Anollés ◽  
Antonio Lagares ◽  
Wolfgang D. Bauer
Keyword(s):  
Rhizobium Meliloti ◽  
Feedback Regulation ◽  
Nodule Formation

Feedback regulation of nodule formation in Hippopha� rhamnoides

1992 ◽  
Vol 144 (1) ◽  
pp. 45-50 ◽  
Author(s):  
Svetlana V. Dobritsa ◽  
Svetlana N. Novik
Keyword(s):  
Feedback Regulation ◽  
Nodule Formation

Symbiotic characteristics of Rhizobium meliloti: and appraisal of the systematic treatment of nodulation and nitrogen fixation interactions between hosts and Rhizobia of diverse origins

1966 ◽  
Vol 17 (6) ◽  
pp. 885 ◽  
Author(s):  
J Brockwell ◽  
FW Hely
Keyword(s):  
Nitrogen Fixation ◽  
Host Species ◽  
Rhizobium Meliloti ◽  
Small Degree ◽  
Nodule Formation ◽  
Systematic Treatment ◽  
Diverse Origin ◽  
Medicago Rugosa ◽  
Medicago Sativa L ◽  
Symbiotic Properties

The symbiotic properties of 42 isolates of Rhizobium meliloti collected from widely separated sites in the upper basin of the Darling River were tested in bacteriologically controlled culture with 18 species and varieties of Medicago, three species of Melilotus, and one species of Trigonella. Seven strains of Rh. Meliloti of commercial interest were included in the experiments for comparative purposes. Nodule formation occurred on all plants in 889 out of 974 symbiotic combinations examined. Only Medicago laciniata (L.) Mill, among the hosts and the isolate from M. laciniata among the rhizobia exhibited distinctive nodule formation behaviour. Nitrogen fixation occurred in 637 combinations. On the basis of nitrogen fixation, eight groups of Rh. Meliloti were recognized; there were nine host groups. The groups could be arranged in an interlocking pattern of increasing host and bacterial specificity. These results, which modified to a small degree the bacterial and host groupings previously reported, strongly suggested that the pattern will be widely applicable to Rh. meliloti of diverse origin. In general, the isolates examined were promiscuous and 24 were capable of effective symbioses in association with 10 or more of the hosts. M. laciniata, Trigonella suavissima Lindl., and Medicago rugosa Desr. were the hosts most highly strain-specific in their requirements for nitrogen fixation, and Medicago sativa L. was the most promiscuous. A system for classifying host species into compatibility groups is proposed.

Feedback regulation of nodule formation in alfalfa

Planta ◽  
1988 ◽  
Vol 175 (4) ◽  
pp. 546-557 ◽  
Author(s):  
G. Caetano-Anoll�s ◽  
W. D. Bauer
Keyword(s):  
Feedback Regulation ◽  
Nodule Formation

Azospirillum effects on susceptibility to Rhizobium nodulation and on nitrogen fixation of several forage legumes

1987 ◽  
Vol 33 (6) ◽  
pp. 510-514 ◽  
Author(s):  
Eli Yahalom ◽  
Yaacov Okon ◽  
Amos Dovrat
Keyword(s):  
Rhizobium Meliloti ◽  
Root Hairs ◽  
Acetylene Reduction Activity ◽  
Nodule Formation ◽  
Medicago Polymorpha ◽  
Reduction Activity ◽  
Colony Forming Units ◽  
Macroptilium Atropurpureum ◽  
Rhizobium Nodulation ◽  
Increased Susceptibility

Azospirillum brasilense Cd cell concentration of 105–107 colony-forming units (cfu)/mL applied 24 h before Rhizobium (106 cfu/mL), increased nodule formation in the non root hair zone, more than twofold, in pouch-grown Medicagopolymorpha and Macroptilium atropurpureum seedlings, compared with Rhizobium alone. The increase in nodule formation in pouch-grown Trifolium alexandrinum following preinoculation with Azospirillum was 20%. The percentage of nodulated seedlings rose from 0 to 25% when Medicago polymorpha was preinoculated with Azospirillum followed by the application of 10 cfu/mL Rhizobium meliloti, a level which by itself was not sufficient to initiate nodule formation. Acetylene reduction activity in Medicago polymorpha and Macroptilium atropurpureum seedlings after inoculation with Azospirillum–Rhizobium was markedly increased. A possible reason for the increased susceptibility to Rhizobium infection may be that Azospirillum stimulates the formation of a larger number of epidermal cells that differentiate into infectable root hairs.

Symbiotic characteristics of Rhizobium meliloti from the brown acid soils of the Macquarie region of New South Wales.

1961 ◽  
Vol 12 (4) ◽  
pp. 630 ◽  
Author(s):  
J Brockwell ◽  
FW Hely
Keyword(s):  
Rhizobium Meliloti ◽  
New South ◽  
New South Wales ◽  
Acid Soils ◽  
Nodule Formation ◽  
Seed Inoculation ◽  
South Wales ◽  
High Level ◽  
Bacterial Groups ◽  
Selection Of

Thirty-three isolates of Rhizobim meliloti were obtained from the brown acid soils of the Macquarie region of New South Wales and their symbiotic behaviour in association with 11 species of Merlicago and three species of Melilotus was investigated in the laboratory. In respect of nodule formation, there were two distinct types of Rhizobiurn and the hosts formed three groups. In respect of nitrogen fixation there were six strain types and seven host, groupings. These host and bacterial groups could be arranged in a series. Several of the strains of rhizobia, and one in particular, were found to fix a high level of nitrogen with a number of hosts, but, except for ;Medicago denticulata Willd. and Melilotus indica (L.) All. which behaved identically in all features of the symbiosis studied, no definit'e groupings on this criterion were apparent in either hosts or bacteria. The possible application of the results to the selection of strains of' Rhizobium meliloti suitable for seed inoculation is discussed.

Ultrastructure of root nodules formed by ineffective strains of Rhizobium meliloti

1974 ◽  
Vol 20 (5) ◽  
pp. 755-758 ◽  
Author(s):  
C. R. MacKenzie ◽  
D. C. Jordan
Keyword(s):  
Rhizobium Meliloti ◽  
Root Nodules ◽  
Plant Cells ◽  
Host Cells ◽  
Nodule Development ◽  
Nodule Formation ◽  
Starch Granules ◽  
Naturally Occurring ◽  
Intimate Association ◽  
Rough Er

In three ineffective associations between Medicago sativa (alfalfa) and Rhizobium meliloti the initial stages of nodule formation, resulting in the release of the bacteria into the host cells, were found to follow the normal pattern of nodule development. In nodule tissue formed by two laboratory-produced ineffective mutants, a rapid disintegration of the invading bacteria was observed to occur shortly after the release of the bacteria into the plant cells. The disintegrating bacteria were in intimate association with large amounts of rough endoplasmic reticulum (ER). An increase in the number of mitochondria occurred at this stage as well and the peripheries of the plant cells were often lined with starch granules. Only occasionally was the stage of enclosing-membrane formation reached. In the third ineffective association, a naturally occurring one, the bacteria were transformed into the nitrogen-fixing or bacteroidal forms and were surrounded by enclosing membranes. Dissolution of the bacteria occurred at a slightly later stage in this association and was again accompanied by a buildup of rough ER. Evidence is presented to suggest that the plant response, as characterized by this ER buildup in these ineffective associations, was a manifestation of nitrogen starvation.

Regulation of syrM and nodD3 in Rhizobium meliloti.

Genetics ◽  
1993 ◽  
Vol 134 (2) ◽  
pp. 435-444 ◽  
Author(s):  
J A Swanson ◽  
J T Mulligan ◽  
S R Long
Keyword(s):  
Rhizobium Meliloti ◽  
Nodule Formation ◽  
Multicopy Plasmid ◽  
Linked Gene ◽  
The Third ◽  
Regulatory Circuit ◽  
Sym Plasmid ◽  
Symbiotic Nodule ◽  
Operon Expression ◽  
Plasmid Genes

Abstract The early steps of symbiotic nodule formation by Rhizobium on plants require coordinate expression of several nod gene operons, which is accomplished by the activating protein NodD. Three different NodD proteins are encoded by Sym plasmid genes in Rhizobium meliloti, the alfalfa symbiont. NodD1 and NodD2 activate nod operons when Rhizobium is exposed to host plant inducers. The third, NodD3, is an inducer-independent activator of nod operons. We previously observed that nodD3 carried on a multicopy plasmid required another closely linked gene, syrM, for constitutive nod operon expression. Here, we show that syrM activates expression of the nodD3 gene, and that nodD3 activates expression of syrM. The two genes constitute a self-amplifying positive regulatory circuit in both cultured Rhizobium and cells within the symbiotic nodule. We find little effect of plant inducers on the circuit or on expression of nodD3 carried on pSyma. This regulatory circuit may be important for regulation of nod genes within the developing nodule.

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