The occurrence of infected cells, with persistent infection threads, in legume root nodules

A survey of the structure of nodules from primitive legume trees was conducted. All genera examined in the subfamily Caesalpinioideae, some from the Papilionoideae, but none from the Mimosoideae had cells in the central, nitrogen-fixing region in which bacteria were confined by host cell wall material in structures resembling infection threads. However, infection of these cells occurred by intercellular spread of rhizobia rather than by infection threads. It is suggested that infection threads may have evolved in infected cells and later extended to early stages of the infection process including entry into root hairs.

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Morphology of root nodules and nodule-like structures formed by Rhizobium and Agrobacterium strains containing a Rhizobium meliloti megaplasmid.

The Journal of Cell Biology ◽

10.1083/jcb.97.3.787 ◽

1983 ◽

Vol 97 (3) ◽

pp. 787-794 ◽

Cited By ~ 38

Author(s):

C H Wong ◽

C E Pankhurst ◽

A Kondorosi ◽

W J Broughton

Keyword(s):

Normal Development ◽

Rhizobium Meliloti ◽

Root Nodules ◽

Root Hairs ◽

Host Cells ◽

Donor Strain ◽

Intercellular Spaces ◽

Infection Threads ◽

Infected Cells ◽

Rhizobium Sp

We examined expression of the megaplasmid pRme41b of Rhizobium meliloti in two different Rhizobium sp. Strains and in Agrobacterium tumefaciens. Transfer of pRme41b into these bacteria was facilitated by insertion of a recombinant plasmid coding for mobilization functions of RP4 into the nif region (Kondorosi, A., E. Kondorosi, C.E. Pankhurst, W. J. Broughton, and Z. Banfalvi, 1982, Mol. Gen. Genet., 188:433-439). In all cases, transconjugants formed nodule-like structures on the roots of Medicago sativa. These structures were largely composed of meristematic cells but they were not invaded by bacteria. Bacteria were found only within infection threads in root hairs, and within intercellular spaces of the outermost cells of the structures. The donor strain of R. meliloti containing pAK11 or pAK12 in pRme41b initially produced nodules on M. sativa that did not fix nitrogen (Fix-). In these nodules, bacteria were released from infection threads into the host cells but they did not multiply appreciably. Any bacteroids formed degenerated prematurely. In some cases, however, reversion to a Fix+ phenotype occurred after 4 to 6 wk. Bacteria released into newly infected cells in these nodules showed normal development into bacteriods.

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Nodulation of Aeschynomene afraspera and A. indica by Photosynthetic Bradyrhizobium Sp. Strain ORS285: The Nod-Dependent Versus the Nod-Independent Symbiotic Interaction

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-04-11-0093 ◽

2011 ◽

Vol 24 (11) ◽

pp. 1359-1371 ◽

Cited By ~ 77

Author(s):

Katia Bonaldi ◽

Daniel Gargani ◽

Yves Prin ◽

Joel Fardoux ◽

Djamel Gully ◽

...

Keyword(s):

Fluorescent Protein ◽

Lateral Roots ◽

Root Hairs ◽

Infection Process ◽

Cortical Cells ◽

Symbiotic Interaction ◽

Root Cortex ◽

Bradyrhizobium Sp ◽

Infected Cells ◽

Green Fluorescent

Here, we present a comparative analysis of the nodulation processes of Aeschynomene afraspera and A. indica that differ in their requirement for Nod factors (NF) to initiate symbiosis with photosynthetic bradyrhizobia. The infection process and nodule organogenesis was examined using the green fluorescent protein–labeled Bradyrhizobium sp. strain ORS285 able to nodulate both species. In A. indica, when the NF-independent strategy is used, bacteria penetrated the root intercellularly between axillary root hairs and invaded the subepidermal cortical cells by invagination of the host cell wall. Whereas the first infected cortical cells collapsed, the infected ones immediately beneath kept their integrity and divided repeatedly to form the nodule. In A. afraspera, when the NF-dependent strategy is used, bacteria entered the plant through epidermal fissures generated by the emergence of lateral roots and spread deeper intercellularly in the root cortex, infecting some cortical cells during their progression. Whereas the infected cells of the lower cortical layers divided rapidly to form the nodule, the infected cells of the upper layers gave rise to an outgrowth in which the bacteria remained enclosed in large tubular structures. Together, two distinct modes of infection and nodule organogenesis coexist in Aeschynomene legumes, each displaying original features.

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Cytological studies of the infection process in nodulating and nonnodulating pea genotypes

Canadian Journal of Botany ◽

10.1139/b89-313 ◽

1989 ◽

Vol 67 (8) ◽

pp. 2435-2443 ◽

Cited By ~ 3

Author(s):

M. F. Le Gal ◽

S. L. A. Hobbs

Keyword(s):

North American ◽

Rhizobium Leguminosarum ◽

Root Hairs ◽

Infection Process ◽

High Concentration ◽

Cortical Cells ◽

Pisum Sativum L ◽

Infection Threads ◽

American Strain ◽

Plant Effect

Pisum sativum L., cv. Afghanistan, does not form nodules with 128C52, a North American strain of Rhizobium leguminosarum. Timing of the abortion of the nodulation process was determined by microscopy in both 'Afghanistan' and nonnodulating 'Trapper,' produced by backcrossing the nonnodulating genes of 'Afghanistan' into 'Trapper,' a North American variety. Three to 5 days after inoculation, we observed deformed roots and localized swellings as well as loosely curled root hairs in these nonnodulating combinations. Rhizobia entered root hairs and epidermal cells, but no infection threads were seen. Cortical cells divided and a nodule meristem was initiated. Some meristematic cells showed abnormal features such as a high concentration of free ribosomes, dilated endoplasmic reticulum often connected to a dilated nuclear envelope, and disrupted mitochondria. Cortical cells around the nodule meristem were devoid of starch grains. Such phenotypes are known to be associated with rhizobial mutants, but in this case a plant effect is responsible.

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Morphogenesis of root nodules in white clover. II. The effect of mutation in genes nod IJ of the microsymbiont upon the nodule structure

Acta Societatis Botanicorum Poloniae ◽

10.5586/asbp.1998.001 ◽

2014 ◽

Vol 67 (1) ◽

pp. 5-22

Author(s):

Barbara Łotocka ◽

Joanna Kopcińska ◽

Władysław Golinowski

Keyword(s):

White Clover ◽

Rhizobium Leguminosarum ◽

Root Nodules ◽

Single Cells ◽

Wild Strain ◽

Root Hairs ◽

Nodule Development ◽

Wild Type ◽

Delayed Reaction ◽

Infection Threads

Morphogenesis of ineffective root nodules initiated on the roots of white clover 'Astra' by the Rhizobium leguminosarum biovar. trifolii strains ANU261 (Tn5 insertion in nod 1 gene) and ANU262 (Tn5 insertion in nod J gene) was investigated. Following changes were observed, as compared to the wild-type nodulation: the exaggerated, not delayed reaction of root hairs; the delay in nodulation with the number of nodules the same as in plants inoculated with a wild strain; the formation and organization of the nodule primordium not changed in comparison with the wild-type nodules; infection threads abnormally branched and diffusing with bacteria deprived of light zone and enriched with storage material; infected cells of bacteroidal tissue abnormally strongly osmiophilic and only slightly vacuolated; symbiosomes with very narrowed peribacteroidal space, subject to premature degradation; abnormal accumulation of starch in the nodule tissues; nodule development blocked at the stage of laterally situated meristem and single nodule bundle; inhibition of divisions in the meristem and vacuolation of its cells; the appearance of single cells with colonies of saprophytic rhizobia embedded in the fibrillar matrix in the old, degraded regions of the bacteroidal tissue.

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Formation and structure of root nodules induced on Macroptilium atropurpureum inoculated with various species of Rhizobium

Canadian Journal of Botany ◽

10.1139/b91-196 ◽

1991 ◽

Vol 69 (7) ◽

pp. 1520-1532 ◽

Cited By ~ 11

Author(s):

Michael J. Trinick ◽

Celia Miller ◽

Paul A. Hadobas

Keyword(s):

Rhizobium Leguminosarum ◽

Rhizobium Meliloti ◽

Root Nodules ◽

Matrix Material ◽

Immunogold Labelling ◽

Infection Threads ◽

Glass Tubes ◽

Infected Cells ◽

Macroptilium Atropurpureum ◽

Nodule Tissue

Fifteen strains of Rhizobium leguminosarum biovar trifolii formed ineffective nodules and (or) nodule-like structures (rhizobia were re-isolated from both structures) on Macroptilium atropurpureum grown in enclosed glass tubes. Bacteria were observed among the parenchyma cells surrounding the nodule-like structures. One variant of R. leguminosarum biovar trifolii (NGR66/ST) isolated from M. atropurpureum formed nodules on this host that exhibited abnormal intercellular and intracellular infection. The bacteria (NGR66/ST) were contained within threadlike structures, surrounded by matrix material. The identities of the Rhizobium strains were confirmed serologically after reisolation and in sections of nodule tissue using immunogold labelling. Rhizobium leguminosarum biovar phaseoli strain NGR76 isolated from Phaseolus vulgaris formed nodules on M. atropurpureum resembling those formed by effective Bradyrhizobium strains. The association was partially effective in nitrogen fixation, and this was reflected in the nodule structure. The percentage of cells infected was lower than that in fully effective nodules. There was a high frequency of infected cells showing degeneration; these were located throughout the nodule tissue and were often adjacent to healthy infected cells. The rhizobia appeared to infect new nodule cells via infection threads, which were abundant both intercellularly and intracellularly in young, mature, and degenerating host nodule cells. Strains of R. leguminosarum biovar viceae and Rhizobium meliloti were unable to induce nodule-like structures on M. atropurpureum. Key words: Macroptilium, Bradyrhizobium, Rhizobium, microscopy, nodule, structure.

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Infection process and sloughing off of rhizobial outer membrane in effective nodules of lima bean

Canadian Journal of Microbiology ◽

10.1139/m82-133 ◽

1982 ◽

Vol 28 (7) ◽

pp. 890-896 ◽

Cited By ~ 10

Author(s):

Arya K. Bal ◽

Peter P. Wong

Keyword(s):

Cell Wall ◽

Outer Membrane ◽

Root Hairs ◽

Lima Bean ◽

Infection Process ◽

Epidermal Cells ◽

Infection Threads ◽

Lima Beans ◽

Membrane Cell ◽

Rhizobium Sp

In addition to infection via root hairs, infection threads originating in epidermal cells after colonization of epidermis have been clearly demonstrated in lima beans infected with Rhizobium sp. 127E15, and this double mode of infection possibly accounts for profuse nodulation of the roots. Sloughing off of the outer membrane (cell wall) was detected after release of rhizobia during bacteroid differentiation in effective nodules.

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Early events in the infection of soybean by Rhizobium japonicum. Time course and cytology of the initial infection process

Canadian Journal of Botany ◽

10.1139/b82-018 ◽

1982 ◽

Vol 60 (2) ◽

pp. 152-161 ◽

Cited By ~ 60

Author(s):

B. Gillian Turgeon ◽

Wolfgang D. Bauer

Keyword(s):

Root Hair ◽

Time Course ◽

Cortical Cell ◽

Root Hairs ◽

Infection Process ◽

Infection Thread ◽

Rhizobium Japonicum ◽

Outer Cortex ◽

Light Microscope Level ◽

Infection Threads

The time course of early infection events in Glycine max following inoculation with Rhizobium japonicum is described. Bacteria became attached to epidermal cells and root hairs within minutes of inoculation. Marked root hair curling occurred within 12 h. Infection thread formation was visible at the light microscope level of resolution about 24 h after inoculation. Infections were observed in short, tightly curled root hairs. These root hairs had not yet emerged at the time of inoculation. Infection threads appeared to originate in pockets formed by contact of the cell wall of the curled root hair with itself. Infection threads in the hairs were multiple and (or) branched. By 48 h, the infection thread(s) had progressed to the base of the root hair but had not yet penetrated into the cortex. Increases in cortical cell cytoplasm and in mitotic division occurred in advance of the penetrating infection thread. A nodule meristem developed in the outer cortex next to the infected root hair by 4 days and was accompanied by cell division across the cortex.

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Investigation of a non-nodulating cultivar of Pisum sativum

Canadian Journal of Botany ◽

10.1139/b76-175 ◽

1976 ◽

Vol 54 (14) ◽

pp. 1633-1636 ◽

Cited By ~ 23

Author(s):

T. L. Degenhardt ◽

T. A. Larue ◽

E. A. Paul

Keyword(s):

Pisum Sativum ◽

Rhizobium Leguminosarum ◽

Root Hairs ◽

Infection Process ◽

Nodule Formation ◽

Temperature Sensitive ◽

Infection Threads

A non-nodulating cultivar of Pisum sativum cv. Afghanistan was studied to characterize the nature and location of the non-nodulating factor. Nodule formation was not temperature sensitive. Rhizobium leguminosarum could exist in the rhizosphere. Root secretions did not decrease nodulation in adjacent normal plants, nor did the proximity of normal plants promote nodulation. Infection threads formed in the root hairs, but nodules were not formed. The infection process apparently aborted, resulting in the formation of swellings on areas of the root where nodulation would normally occur. Grafting experiments indicate that the factor preventing nodulation is in the root and is not translocated from the cotyledon or plant top.

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Morphogenesis of root nodules in white clover. III. The effect of mutation in nod IJ genes of the microsymbiont upon the DNA level in the host tissue

Acta Societatis Botanicorum Poloniae ◽

10.5586/asbp.1998.002 ◽

2014 ◽

Vol 67 (1) ◽

pp. 23-29

Author(s):

Barbara Łotocka ◽

Władysław Golinowski

Keyword(s):

White Clover ◽

Rhizobium Leguminosarum ◽

Root Nodule ◽

Nuclear Dna ◽

Root Nodules ◽

Root Hairs ◽

Infection Threads ◽

Dna Contents ◽

Mutant Strains ◽

Nuclear Dna Contents

On the basis of cytophotometric measurements a slightly increased DNA level in the nuclei of curled root hairs containing infection threads was observed in white clover inoculated with wild and mutant strains of Rhizobium leguminosarum biovar. trifolii, as compared to normal root hairs of te same plants. Cells of the root nodule primordia in 72 h after the inoculation, as compared to the root primary cortex, demonstrated an increased level of the nuclear DNA. No differences were observed in the nuclear DNA contents in individual layers of the cortex of the 28 day-old nodules. Generally it was low, varying from 2c to 4c. The meristematic and bacteroidal tissues in the effective nodules were characterized by a higher DNA level, as compared to the respective zones in ineffective nodules induced with the strains ANU261 (nod I*) and ANU262 (nod J*). The DNA level in the effective bacteroidal tissue varied from 4c to 32c, while in the tissue containing the strain ANU26l only the 2c-8c nuclei could be found and in the tissue with the strain ANU262 - the 4c-16c nuclei.

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Cytoplasmic bridge formation in the nodule apex of actinorhizal root nodules

Canadian Journal of Botany ◽

10.1139/b99-078 ◽

1999 ◽

Vol 77 (9) ◽

pp. 1351-1357 ◽

Cited By ~ 2

Author(s):

R Howard Berg

Keyword(s):

Structural Changes ◽

Root Nodules ◽

Parenchyma Cell ◽

Infection Process ◽

Infection Thread ◽

Cytoplasmic Bridge ◽

Cortical Cells ◽

Infection Threads ◽

Related Plant ◽

Cytoplasmic Bridges

High-pressure frozen - freeze-substituted actinorhizal root nodules of several distantly related plant genera were used to document the sequence of structural changes in cortical cells of the nodule apex that happened prior to their infection. The sequence of mobilization of the plant cell cytoplasm requisite to infection by Frankia was (i) penetration of the parenchyma cell vacuole by cytoplasmic strands, which contained microtubules; (ii) movement of the nucleus and other organelles (Golgi stacks, endoplasmic reticulum, mitochondria), involved later in growth of the infection thread, to the cell center on these strands; (iii) thickening of some of these strands generally located at midpoints of the wall, forming cytoplasmic bridges (preinfection threads); and (iv) infection of the cell by initiation of infection threads (containing Frankia) within the cytoplasmic bridges. The infection thread was caged in microtubules that were oriented along its axis, suggesting the cytoskeleton had a major role in the infection process, perhaps guiding the growth of the infection thread across the cell. The coalignment of cytoplasmic bridges, along several cells, towards the advancing microsymbiont suggested Frankia secretes a diffusible signal eliciting this host response.Key words: actinorhiza, cryofixation, development, infection, microtubules, symbiosis.

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