Root hair infection process and myconodule formation on Alnus incana by Penicillium nodositatum

1994 ◽  
Vol 72 (7) ◽  
pp. 955-962 ◽  
Author(s):  
Jeanine Sequerra ◽  
André Capellano ◽  
Monique Faure-Raynard ◽  
André Moiroud
Keyword(s):  
Root Hair ◽  
Light And Electron Microscopy ◽  
Root Hairs ◽  
Infection Process ◽  
Initial Contact ◽  
Alnus Incana ◽  
Cortical Cells ◽  
Infected Root ◽  
Root Hair Infection ◽  
Polysaccharide Matrix

Penicillium nodositatum infects the roots of alder trees and induces the formation of structures called myconodules, which are similar to young actinorhizae. Root infection of Alnus incana by P. nodositatum as well as myconodule development were studied by light and electron microscopy and observations were compared with those described for the infection by Frankia spp. We have established an obvious homology between the early steps of the infection caused by both microorganisms. The presence of the fungus near the roots induces deformation of root hairs. The infection site is probably localized in a folding of a deformed hair. As soon as hyphae penetrate into the hair, they become enclosed in a polysaccharide matrix. Initially, P. nodositatum colonizes a region near the infected root hair that may correspond to a slightly developed prenodule. Then a nodular primordium is initiated at some distance from the initial contact and the new nodular cortex is invaded by the fungus. The zone of infection is limited to the cortical cells by a barrier of tannins. Myconodules remain small and unilobed and have an outer morphology similar to that of an incompatible Frankia nodule. Key words: Alnus, myconodule formation, Penicillium, root hair infection.

The structural basis for infection of root hairs of Trifolium repens by Rhizobium

1981 ◽  
Vol 59 (9) ◽  
pp. 1647-1664 ◽  
Author(s):  
Dale A. Callaham ◽  
John G. Torrey
Keyword(s):  
Trifolium Repens ◽  
Root Hair ◽  
Hydrolytic Enzymes ◽  
Root Hairs ◽  
Structural Basis ◽  
Physical Constraints ◽  
Root Hair Cell ◽  
Host Cytoplasm ◽  
Infected Root ◽  
Root Hair Infection

Root hair infection of Trifolium repens L. by Rhizobium trifolii was investigated with regard to the structural basis of infection thread origin. Most infected root hairs were shown to have in common an enclosed region at-the site of thread origin formed by specialized root hair growth or contacts. Electron micrographs of diverse infection sites showed in every case a degradation of the root hair wall at the site of thread origin within the enclosure. The thread wall is a new layer formed by apposition of material by the host cytoplasm near the penetrated wall and surrounding the break as encapsulation of the invading rhizobia. It is suggested that rhizobial enzymes provide for degradative penetration of the root hair cell wall and that localized concentrated activity of hydrolytic enzymes as well as protection from cell lysis is favored by physical constraints provided by the deformed root hair enclosures.

scholarly journals Invasion by Invitation: Rhizobial Infection in Legumes

2011 ◽  
Vol 24 (6) ◽  
pp. 631-639 ◽  
Author(s):  
Jeremy D. Murray
Keyword(s):  
Root Hair ◽  
Root Hairs ◽  
Infection Process ◽  
Nodule Development ◽  
Nod Factors ◽  
Cortical Cells ◽  
Root Cortex ◽  
Root Hair Cell ◽  
Cytoplasmic Bridges ◽  
Cytoskeletal Rearrangements

Nodulation of legume roots typically begins with rhizobia attaching to the tip of a growing root-hair cell. The attached rhizobia secrete Nod factors (NF), which are perceived by the plant. This initiates a series of preinfection events that include cytoskeletal rearrangements, curling at the root-hair tip, and formation of radially aligned cytoplasmic bridges called preinfection threads (PIT) in outer cortical cells. Within the root-hair curl, an infection pocket filled with bacteria forms, from which originates a tubular invagination of cell wall and membrane called an infection thread (IT). IT formation is coordinated with nodule development in the underlying root cortex tissues. The IT extends from the infection pocket down through the root hair and into the root cortex, where it passes through PIT and eventually reaches the nascent nodule. As the IT grows, it is colonized by rhizobia that are eventually released into cells within the nodule, where they fix nitrogen. NF can also induce cortical root hairs that appear to originate from PIT and can become infected like normal root hairs. Several genes involved in NF signaling and some of the downstream transcription factors required for infection have been characterized. More recently, several genes with direct roles in infection have been identified, some with roles in actin rearrangement and others with possible roles in protein turnover and secretion. This article provides an overview of the infection process, including the roles of NF signaling, actin, and calcium and the influence of the hormones ethylene and cytokinin.

Cytological and histochemical characteristics of the axenic root surface of Alnus glutinosa

1986 ◽  
Vol 64 (10) ◽  
pp. 2216-2226 ◽  
Author(s):  
Yves Prin ◽  
Mireille Rougier
Keyword(s):  
Cell Wall ◽  
Root Hair ◽  
Root Hairs ◽  
Root Apex ◽  
Alnus Glutinosa ◽  
Root Surface ◽  
Infection Process ◽  
Root Cap ◽  
A Cell ◽  
Histochemical Tests

The aim of the present study was to investigate the Alnus root surface using seedlings grown axenically. This study has focused on root zones where infection by the symbiotic actinomycete Frankia takes place. The zones examined extend from the root cap to the emerging root hair zone. The root cap ensheaths the Alnus root apex and extends over the root surface as a layer of highly flattened cells closely appressed to the root epidermal cell wall. These cells contain phenolic compounds as demonstrated by various histochemical tests. They are externally bordered by a thin cell wall coated by a thin mucilage layer. The root cap is ruptured when underlying epidermal cells elongate, and cell remnants are still found in the emerging root hair zone. Young emerging root hairs are bordered externally by a cell wall covered by a thin mucilage layer which reacts positively to the tests used for the detection of polysaccharides, glycoproteins, and anionic sites. The characteristics of the Alnus root surface and the biological function of mucilage and phenols present at the root surface are discussed in relation to the infection process.

Root hair deformation in the infection process of Alnus rubra

1983 ◽  
Vol 61 (11) ◽  
pp. 2863-2876 ◽  
Author(s):  
Alison M. Berry ◽  
John G. Torrey
Keyword(s):  
Root Hair ◽  
Cell Walls ◽  
Root Hairs ◽  
Infection Process ◽  
Alnus Rubra ◽  
Pseudomonas Cepacia ◽  
Developmental Studies ◽  
Experimental Conditions ◽  
Root Hair Cell ◽  
Root Hair Deformation

Structural and cell developmental studies of root hair deformation in Alnus rubra Bong. (Betulaceae) were carried out following inoculation with the soil pseudomonad Pseudomonas cepacia 85, alone or in concert with Frankia, and using axenically grown seedlings. Deformational changes can be observed in elongating root hairs within 2 h of inoculation with P. cepacia 85. These growing root hairs become branched or multilobed and highly modified from the single-tip growth of axenic root hairs. The cell walls of deformed hairs are histologically distinctive when stained with the fluorochrome acridine orange. Filtrate studies using P. cepacia 85 suggest that the deforming substance is not a low molecular weight compound. Root hair deformation and the associated wall histology are host specific in that Betula root hairs show none of these responses when grown and inoculated in the experimental conditions described. The bacterially induced changes in root hair cell walls during deformation may create a chemically and physically modified substrate for Frankia penetration, and the deformation itself may serve to entrap and enclose the filamentous organism, allowing wall dissolution and entry. Thus these events represent a complex host response as a precondition to successful nodulation.

Structure and ontogeny of Betula alleghaniensis – Pisolithus tinctorius ectomycorrhizae

1990 ◽  
Vol 68 (3) ◽  
pp. 579-593 ◽  
Author(s):  
H. B. Massicotte ◽  
R. L. Peterson ◽  
C. A. Ackerley ◽  
L. H. Melville
Keyword(s):  
Root Hairs ◽  
Root Surface ◽  
Pisolithus Tinctorius ◽  
Initial Contact ◽  
Broad Host Range ◽  
Betula Alleghaniensis ◽  
Cortical Cells ◽  
Structural Modifications ◽  
Hartig Net ◽  
Primary Roots

The ontogeny and ultrastructure of ectomycorrhizae synthesized between Betula alleghaniensis (yellow birch) and Pisolithus tinctorius, a broad host range fungus, were studied to determine the structural modifications in both symbionts during ectomycorrhiza establishment. A number of stages, including initial contact of hyphae with the root surface, early mantle formation, and mature mantle formation, were distinguished. Interactions between hyphae and root hairs were frequent. As a paraepidermal Hartig net developed, root epidermal cells elongated in a radial direction, but wall ingrowths were not formed. Repeated branching of Hartig net hyphae resulted in extensive fine branches and the compartmentalization of hyphal cytoplasm. Nuclei and elongated mitochondria were frequently located in the narrow cytoplasmic compartments, and [Formula: see text] thickenings developed along walls of cortical cells in primary roots.

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

2011 ◽  
Vol 24 (11) ◽  
pp. 1359-1371 ◽  
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.

Histopathology of Pythium infected strawberry roots

1972 ◽  
Vol 50 (5) ◽  
pp. 1091-1096 ◽  
Author(s):  
S. Nemec
Keyword(s):  
Root Hairs ◽  
Petri Dish ◽  
Root Tip ◽  
Test Results ◽  
Root Tips ◽  
Cortical Cells ◽  
Pythium Irregulare ◽  
Infected Root ◽  
Cortical Infection ◽  
Host Parasite

Host–parasite interactions between eight Pythium species, previously isolated from necrotic strawberry root tissue, and Fragaria × ananassa Duch. runner plant main roots were studied. When excised roots were placed in water on petri dish cultures, P. rostratum and P. hypogenum infection was limited to the root tip epidermis. Pythium irregulare, P. perniciosum, P. dissotocum, P. sylvaticum, P. ultimum, and unidentified isolate 1E penetrated the epidermis several centimeters along the zone of maturation. Penetration occurred most frequently through root hairs by hyphae; resulting infections usually stopped in the epidermis or adjacent cortex, and here hyphae formed sporangium-like structures, oogonia, and oospores. Extensive cortical infection by hyphae was primarily limited to the zone of elongation. Extent of epidermal and cortical infection in roots grown in soil with P. irregulare, P. dissotocum, and P. sylvaticum was similar to petri dish test results. Stelar infection by P. sylvaticum and P. dissotocum occurred mainly in phloem cells, but did not advance far into the region of maturation. Numerous oogonia formed in infected steles and usually in adjacent cortical cells. Infected roots ranged from a white to grey, water-soaked color. Extensively infected root tips typically were unhealthy, succulent, and thin.

Callose-containing deposits in relation to root-hair infections of Alnus rubra by Frankia

1990 ◽  
Vol 68 (4) ◽  
pp. 798-802 ◽  
Author(s):  
A. M. Berry ◽  
M. E. McCully
Keyword(s):  
Electron Microscopy ◽  
Hair Cells ◽  
Root Hair ◽  
Vascular Tissue ◽  
Root Hairs ◽  
Alnus Rubra ◽  
Blue Fluorescence ◽  
Electron Dense Material ◽  
Transmission Electron ◽  
Infected Root

Light microscopy, aniline-blue fluorescence histochemistry, and transmission electron microscopy were used to elucidate the nature of localized wall deposition in infected and uninfected root hairs on nodulated roots of Alnus rubra Bong, inoculated with the nitrogen-fixing symbiont, Frankia HFPAr13. Callose-containing papillae were found only in epidermal hair cells and not in cortical or vascular tissue. At the site of successful root-hair wall penetration, transfer cell-like wall ingrowths were elaborated, but callose was not detected. At sites of arrested root-hair infections, complex deposits consisting of callose, fibrillar components, and electron-dense material surrounded the incipient hyphal infection. The cytoplasm of root hairs containing arrested infections was deteriorated compared with successfully infected root hairs.

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

1989 ◽  
Vol 67 (8) ◽  
pp. 2435-2443 ◽  
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.

Light and electron microscopy of a host–fungus interaction in the roots of some epiphytic ferns from Costa Rica

1995 ◽  
Vol 73 (7) ◽  
pp. 991-996 ◽  
Author(s):  
E. Schmid ◽  
F. Oberwinkler ◽  
L. D. Gómez
Keyword(s):  
Electron Microscopy ◽  
Costa Rica ◽  
Matrix Material ◽  
Light And Electron Microscopy ◽  
Root Hairs ◽  
Host Cells ◽  
Cortical Cells ◽  
Host Fungus ◽  
Hyphal Coils ◽  
Uniform Diameter

The roots of 11 epiphytic fern species from the genera Elaphaglossum, Peltapteris, Hymenophyllum, Grammitis, and Lellingeria were studied by means of light and electron microscopy. All species showed a similar association with an ascomycete that traversed the root hairs and formed intracellular hyphal coils within cytoplasmic epidermal and outer cortical cells. The unbranched fungal hyphae were of a uniform diameter. They were surrounded by a flocculent matrix material and by the host plasmalemma. Cytoplasmic hyphae also occurred within degenerated host cells. The host–fungus interaction showed similarities to Ericoid mycorrhizae. Key words: ferns, mycorrhiza, ascomycete, ultrastructure, Costa Rica.

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