[Show abstract][Hide abstract] ABSTRACT: The structure of roots, rhizomes, or subterranean scale leaves of mycoheterotrophic (MH) plants intimately linked to the association with soil fungi is of critical ecological relevance because these plants essentially depend upon fungi for their carbon and perhaps other nutrient needs. Hence, the subterranean organs of MH plants often show remarkable morphological and anatomical adaptations to meet their specific requirements. This chapter addresses the importance of morphology and anatomy to complement modern methods for understanding the fungal colonization patterns in MH plants and their relationships to function. We summarize the current knowledge of structural aspects of the underground parts (except for Afrothismia) of MH plants ranging from bryophytes to angiosperms, the latter in systematical order following the Angiosperm Phylogeny Group. We focus on the visibly achlorophyllous species, and only include the partially mycoheterotrophs where they add to the common picture. The final section interprets the available information in terms of detecting phylogenetic trends of MH plants, in order to understand their evolutionary history.
[Show abstract][Hide abstract] ABSTRACT: Ectomycorrhizae synthesized between Alpova diplophloeus and Alnus rubra are of two morphological types: one with a mantle formed along the entire length of the lateral roots and the other, the clavate type, with the mantle confined to the apical portion of the laterals. The morphology of the mycorrhiza is dependent on the stage of lateral root elongation at the time of colonization by fungal hyphae. Clavate mycorrhizae form on lateral roots that have already elongated at the time of fungal colonization. Fungal hyphae interact with root hairs at the base of clavate mycorrhizae. Mantles of both types are fairly compact with few extramatrical hyphae. Hartig net hyphae, which branch profusely primarily in the radial direction, are confined to the epidermis and midway along the radial walls of the outer layer of cortical cells. Second-order lateral root primordia are initiated in the mature Hartig net zone. Cells in the outer layer of the cortex of mycorrhizal roots collapse during fixation, indicating the possible presence of a barrier in the cell wall blocking the ingress of fixative.
Full-text · Article · Feb 2011 · Canadian Journal of Botany
[Show abstract][Hide abstract] ABSTRACT: Cenococcum geophilum sclerotium morphology, germination, and formation in pure culture and growth pouches is described. On agar, germination of most field-collected sclerotia occurred within 30 days. In vitro attempts to initiate sclerotia succeeeded to varying degrees for 20 of the 22 isolates (collected in three main habitats in Oregon) in agar or peat – vermiculite but not in liquid culture. Sclerotium formation was initiated in 1-month-old cultures by branching, lateral growth, and subsequent septation of hyphae. Surface cells of compact hyphae of young sclerotia elongated, became irregularly arranged, and melanized. In growth pouches, sclerotium initials developed on the paper wick from a hyphal mat formed from convoluted hyphae. Mature sclerotia appeared as small spherical structures with linear hyphae radiating out from the surface. Sections revealed a well-differentiated rind and a medulla with pseudoparenchymatous organization. Numerous nuclei and vacuoles were distributed in both rind and medullary hyphae. Key words: Cenococcum, sclerotium, initiation, in vitro.
Full-text · Article · Feb 2011 · Canadian Journal of Botany
[Show abstract][Hide abstract] ABSTRACT: The xanthene dyes sulforhordamine G, phloxine B, rose Bengal, and 4,5,6,7-tetrachloroflorescein were used as fluorochromes for laser scanning confocal microscopy of LR-White resin-embedded mycorrhizae. Sulforhodamine G was the most effective dye, giving an even staining of cell components throughout the material, with minimal background fluorescence of LR-White resin. Confocal microscopy of stained blocks of tissue on a slide, viewed without the use of a coverslip, revealed the three-dimensional nature of various mycorrhizal structures; these structures included arbuscules, vesicles, and coiled hyphae in arbuscular mycorrhizae; coiled hyphae in orchid mycorrhizae; mantle and Hartig net hyphae in ectomycorrhizae; and intracellular hyphae in arbutoid mycorrhizae. Sections mounted on slides viewed with confocal microscopy provided exceptional clarity of fungal form and cytoplasmic contents and showed the relationship to the plant cells, also with negligible background fluorescence. Mounting and staining blocks of resin-embedded material provided a fast and effective technique for the visualization of a variety of plant and fungal tissues. Stain penetration in whole-mounted samples was sufficient to reconstruct clear three-dimensional images using confocal microscopy.Key words: mycorrhizae, xanthene dyes, confocal microscopy, resin embedding.
Full-text · Article · Feb 2011 · Canadian Journal of Botany
[Show abstract][Hide abstract] ABSTRACT: All members of the Monotropoideae (Ericaceae), including the species, Allotropa virgata and Pleuricospora fimbriolata, are mycoheterotrophs dependent on associated symbiotic fungi and autotrophic plants for their carbon needs. Although the fungal symbionts have been identified for A. virgata and P. fimbriolata, structural details of the fungal-root interactions are lacking. The objective of this study was, therefore, to determine the structural features of these plant root-fungus associations. Root systems of these two species did not develop dense clusters of mycorrhizal roots typical of some monotropoid species, but rather, the underground system was composed of elongated rhizomes with first- and second-order mycorrhizal adventitious roots. Both species developed mantle features typical of monotropoid mycorrhizas, although for A. virgata, mantle development was intermittent along the length of each root. Hartig net hyphae were restricted to the host epidermal cell layer, and fungal pegs formed either along the tangential walls (P. fimbriolata) or radial walls (A. virgata) of epidermal cells. Plant-derived wall ingrowths were associated with each fungal peg, and these resembled transfer cells found in other systems. Although the diffuse nature of the roots of these two plants differs from some members in the Monotropoideae, the structural features place them along with other members of the Monotropoideae in the "monotropoid" category of mycorrhizas.
[Show abstract][Hide abstract] ABSTRACT: Most species in the family Cistaceae are found in the Mediterranean basin. Several hosts are of special interest, owing to their associations with truffle species, while many are important as pioneer plants in disturbed areas and in soil stabilization. For these reasons, understanding their root systems and their associated fungal symbionts is important. Most studies of the structure of mycorrhizas in this family involve two genera, Cistus and Helianthemum. The present study examines structural features of mycorrhizas in two North American species, Hudsonia ericoides L. and Hudsonia tomentosa Nutt. Root systems of both species are highly branched with most fine roots colonized by mycorrhizal fungi. Based on morphological features, several mycorrhizal fungi were identified; structural details also provided evidence of more than one fungal symbiont for each host species. All mycorrhizas had a multi-layered fungal mantle and Hartig net hyphae confined to radially elongated epidermal cells; no intracellular hyphae were observed. Although the Hartig net was confined to the epidermis, the outer row of cortical cell walls lacked suberin, a known barrier to fungal penetration. Mycorrhizas in H. ericoides and H. tomentosa differed from those of Cistus and Helianthemum species that have a Hartig net that extends into the root cortex, as well as frequently present intracellular hyphae.
[Show abstract][Hide abstract] ABSTRACT: Achlorophyllous plants that are dependent on an association with fungi linked to photosynthetic plants for their carbon source are known as mycoheterotrophs. Arachnitis uniflora Phil., a monotypic member of the monocotyledonous family Corsiaceae, fits this category, as it relies on a glomalean fungus belonging to Glomus Group A for carbon acquisition. Although basic structural features of root colonization have been reported for A. uniflora, the nutrient exchange interface has not been studied. This is the first study to use confocal microscopy, transmission electron microscopy, and cytochemical procedures to study the interface between a glomalean fungus and the roots of a mycoheterotrophic species. Results showed that arbuscules are never formed, and that the ''vesicles in bundles'' reported earlier are unlike typical glomalean vesicles, in that they form in clusters by the enlargement of hyphal branches and have a complex multilayered wall. The thick inner wall layer consists primarily of β-1,3-glucans (callose) and is surrounded by a thin outer layer of chitin. Each structure is surrounded by host cell wall material and a perifungal membrane, suggesting an involvement in nutrient exchange. The cytoplasm contains a complex of small β-1,3-glucan-containing vacuoles, lipid bodies, endobacteria, and many nuclei. These structures enlarge to occupy most of the cortical cell volume and then degrade, releasing lipids and other materials into the host cell. We suggest that these structures should not be equated with typical glomalean vesicles but are unique structures that may be involved, along with the hyphal coils, in nutrient acquisition by the host.
[Show abstract][Hide abstract] ABSTRACT: summarySeedlings of Pseudotsuga menziesii (Mirb.) Franco, Pinus ponderosa Dougl. ex Laws, Arbutus menziesii Pursh., and cuttings of Arclast apliylos uva-ursi (L.) Spreng were grown in monoculture and in conifer-hardwood dual-culture combinations in the glasshouse and inoculated with spore slurries of six Rhizopogon species. The primary objectives were to assess and compare the pattern of host specificity between symbionts and to study the influence of co-cultured plants on ecromycorrhiza development. The Rhizopogon spp. ranged from genus-specific to multiple-host compatible. In monoculture, four Rhisopogon sp, (R. ellenae Smith, R. occidentalis Zeller & Dodge, R. smithii Hosfnrd and R. subcaerulescens Smith) formed ectomycorrhizas with Pinus ponderosa, and two Rhizopogon sp. (R. parksii Smith and R. vinicolor Smith) formed ectomycorrhizas with Pseudotsuga menziesii. None of the fungi tested developed ectomycorrhizas on Arbutus menziesii or Arctostaphylos uvaursi in monoculture. In dual culture, three of the four Rhizopogon species (R. ellenae, R. occidentalis and R. subcaerulescens) that formed ectomycorrhizas on Pinus ponderosa, formed some ectomycorrhizas on Arbutus menziesii and Arrtastaphvlos uva-ursi. Rhizopogon parksii and R. tinicoior only formed ectomycorrhizas on Pseudotsuga mensiesti.
[Show abstract][Hide abstract] ABSTRACT: Genera in the tribe Pyroleae (subfamily Monotropoideae, family Ericaceae) occur as understory plants in northern temperate zones where some form major components of ecosystems. Most have been poorly studied in terms of their association with symbiotic fungi. In this study, colonization patterns of mycorrhizal roots of five members of the Pyroleae (Pyrola asarifolia Michx., Pyrolaachlorantha Sw., Orthilia secunda (L.) House, Chimaphila umbellata (L.) W. Bart., Moneses uniflora (L.) Gray) were explored. Root samples were processed for light, fluorescence, and laser scanning confocal, scanning electron, and transmission electron microscopy, as well as for immunocytochemistry. Roots of all species had enlarged epidermal cells containing hyphal complexes, Hartig nets confined to the epidermis, and mantles. Epidermal cells were penetrated by hyphae originating from the Hartig net at more than one site either along the inner tangential wall or radial walls. The outer tangential wall of epidermal cells of all species, except M.auniflora, was thicker than radial and inner tangential walls and consisted of two layers, the outer containing nonesterified pectins that were labeled with JIM 5 antibodies. Radial walls and inner tangential walls did not label, but cortical cell walls did. Intracellular hyphal complexes developed initially around centrally positioned, enlarged epidermal cell nuclei and, through branching, occupied most of the cell volume. Senescence and degradation of the complexes followed. The fungal species in these symbiotic associations may be important functionally in nutrient exchange, as well as in contributing to broader linkages with other hosts in these plant communities.
[Show abstract][Hide abstract] ABSTRACT: Arbuscular mycorrhizal fungi, obligate symbionts of most plant species, are able to accumulate heavy metals, thereby, protecting plants from metal toxicity. In this study, the ultrastructural localization of Zn, Cu, and Cd in the extraradical mycelium and spores of the arbuscular mycorrhizal fungus Glomus intraradices grown in monoxenic cultures was investigated. Zinc, Cu, or Cd was applied to the extraradical mycelium to final concentrations of 7.5, 5.0, or 0.45 mmol/L, respectively. Samples were collected at time 0, 8 h, and 7 days after metal application and were prepared for rapid freezing and freeze substitution. Metal content in different subcellular locations (wall, cytoplasm, and vacuoles), both in hyphae and spores, was determined by energy-dispersive X-ray spectroscopy. In all treatments and fungal structures analysed, heavy metals accumulated mainly in the fungal cell wall and in the vacuoles, while minor changes in metal concentrations were detected in the cytoplasm. Incorporation of Zn into the fungus occurred during the first 8 h after metal addition with no subsequent accumulation. On the other hand, Cu steadily accumulated in the spore vacuoles over time, whereas Cd steadily accumulated in the hyphal vacuoles. These results suggest that binding of metals to the cell walls and compartmentalization in vacuoles may be essential mechanisms for metal detoxification.
No preview · Article · Mar 2008 · Canadian Journal of Microbiology
[Show abstract][Hide abstract] ABSTRACT: Pityopus californicus (Eastw.) H. F. Copel., a monotypic member of the Monotropoideae in the family Ericaceae, is a myco-heterotrophic species with distribution limited to the Pacific Northwest of the USA. Young embryos of P. californicus developed mycorrhizal associations in seed packets that had been buried for up to 681 days, suggesting that seeds of P. californicus may require the presence of a fungus to achieve germination. Samples of nongerminated seeds and early stages in embryo and root development were subsequently processed for light microscopy, histochemistry, and transmission electron microscopy (TEM). Nongerminated seeds possessed a thick testa, lacked a shoot and root meristem, and consisted of an embryo with large parenchymatous cells containing protein bodies and starch grains as storage reserves. In the earliest developmental stage (seed coat still attached), fungal hyphae were present on the testa surface and between the testa and embryo. This stage was followed by embryo elongation, the organization of a root apical meristem, and the development of a well-developed fungal mantle surrounding the elongated embryo. At least two morphotypes were identified based on structural characteristics of the mantle. One of these, with ascomycetous septa, had Cenococcum-like features. Late-stage embryo/early root development revealed a typical mantle and Hartig net, with fungal pegs penetrating the outer tangential walls of epidermal cells. Transfer cell-like deposits of wall material, similar to those described in Monotropa spp., enclosed fungal pegs. The development of a Hartig net and fungal pegs suggests that nutrient exchange interfaces are required for seedling development.
[Show abstract][Hide abstract] ABSTRACT: Arachnitis uniflora, a myco-heterotrophic plant species, has fleshy tuberous roots colonized by the arbuscular mycorrhizal fungal genus Glomus (Phylum Glomeromycota). These roots produce apical and lateral propagules, both reported here for the first time. The objective of the study was to characterize the ontogeny and structure of the propagules, and to determine their function. Scanning electron microscopy, laser scanning confocal microscopy and light microscopy were used to study the ontogeny and structure of the propagules. Propagules developed either from cortical parenchyma cells or from cells immediately beneath the root cap; they developed a shoot meristem and cells in the basal region which were colonized by various fungal structures including hyphae and vesicles. These propagules may detach from the roots, establishing new plants.
[Show abstract][Hide abstract] ABSTRACT: The extraradical mycelium of ectomycorrhizas is comprised of a network of hyphae that may initiate rhizomorphs, sclerotia and sexual reproductive structures. The development of these structures requires photosynthates produced by host trees. In this study, the initiation and early development of Laccaria bicolor (Maire) Orton fruitbodies (basidiocarps) were studied. Seedlings of Pinus resinosa Ait. and Pinus sylvestris L. were colonized by L. bicolor, a broad host epigeous ectomycorrhizal basidiomycetous fungal species, in growth pouches. Ectomycorrhizas with an extensive extraradical mycelium formed on short roots within 7-12 days after fungal inoculum was introduced. Numerous sites of hyphal aggregation, many of which subsequently developed into basidiocarp primordia, were initiated in the extraradical mycelium. Initial changes in aggregating hyphae included swelling and branching followed by growth of hyphae perpendicular to the paper wick in growth pouches. A stipe and a pileus primordium developed but none of these basidiocarp primordia matured. Distinct regions were evident in the stipe and pileus when sections were stained by various methods. Loose hyphae at the apex and periphery of the pileus were separated by mucilage. In Petri dishes with vermiculite as the substrate, basidiocarps of Laccaria laccata formed in ectomycorrhizal associations with Pinus sylvestris, developed a mature pileus with an hymenium and mature basidiospores.
[Show abstract][Hide abstract] ABSTRACT: A combination of light microscopy (including differential interference contrast) and laser scanning confocal microscopy was used to document the colonization patterns of epidermal cells and details of intracellular hyphal complexes of five native ericaceous hosts: Vaccinium oxycoccos L. (bog cranberry), Ledum groenlandicum Oeder. (Labrador tea), Vaccinium myrtilloides L. (velvet-leaf blueberry), Kalmia angustifolia L. (sheep laurel), and Gaultheria procumbens L. (wintergreen). Colonization patterns, hyphal complex morphology, and the structure of thick-walled epidermal cells varied considerably among hosts. Multiple hyphal connections were observed between adjacent epidermal cells, indicating that one fungal entry point may result in the colonization of more than one epidermal cell. Further field observations combined with fungal isolations from field-collected plants, identification, and reinoculation studies of other species in the large Ericaceae family are required to determine the full range of structural details in ericoid mycorrhizas.
Full-text · Article · Aug 2005 · Canadian Journal of Botany
[Show abstract][Hide abstract] ABSTRACT: The annual developmental cycle of tuberous roots of Ranunculus asiaticus was studied with respect to structure and content of their cells, to understand how these roots are adapted to desiccation, high temperature and rehydration. Light microscopy, histochemical analysis, and protein analyses by SDS-PAGE were employed at eight stages of annual root development. During growth and maturation of the roots, cortical cells increased in size and their cell walls accumulated pectin materials in a distinct layer to the inside of the primary walls, with pits between adjoining cells. The number of starch granules and protein bodies also increased within the cells. Several discrete proteins accumulated. Following quiescence and rehydration of the roots there was a loss of starch and proteins from the cells, and cell walls decreased in thickness. The resurrection geophyte R. asiaticus possesses desiccation-tolerant annual roots. They store carbon and nitrogen reserves within their cells, and pectin within the walls to support growth of the plant following summer quiescence and rehydration.
[Show abstract][Hide abstract] ABSTRACT: Species in the subfamily Monotropoideae (family Ericaceae) are achlorophyllous and myco-heterotrophic. They have become highly specialized in that each plant species is associated with a limited number of fungal species which in turn are linked to autotrophic plants. This study provides an updated and comprehensive examination of the anatomical features of two species that have recently received attention with respect to their host-fungal specificity. Root systems of Monotropa uniflora and Pterospora andromedea collected from the field were characterized by light microscopy and scanning electron microscopy. All roots of both species were associated with fungi, each root having a well-developed mantle, paraepidermal Hartig net, and intracellular "fungal pegs" within epidermal cells. The mantle of M. uniflora was multi-layered and numerous outer mantle hyphae developed into cystidia of two distinct morphologies. Large calcium oxalate crystals were present, primarily on the mantle surface. The outer mantle of P. andromedea was more loosely organized, lacked cystidia, and had smaller plate-like as well as cylindrical crystals on the surface and between outer mantle hyphae. Fungal pegs in M. uniflora originated from inner mantle hyphae that penetrated the outer tangential wall of epidermal cells; in P. andromedea, these structures were initiated either from inner mantle hyphae or Hartig net hyphae and penetrated radial walls of epidermal cells. With respect to function, fungal pegs occurred frequently in both host species and, although presumed to be the sites of active nutrient exchange, no direct evidence exists to support this. Differences between these two monotropoid hosts, resulting from the mycorrhizal fungi with which each associates, are discussed.
[Show abstract][Hide abstract] ABSTRACT: Needles of Pinus strobus (white pine) were cleared and stained to survey the occurrence and location of Lophodermium sp., a fungal endophyte. Cytoplasmically dense endophytic hyphae with a pronounced lobed morphology and containing lipid bodies were localized intercellularly between the epidermis and hypodermis. These fungal infections did not appear quiescent, but rather exhibited signs of continual slow growth. A few associated host cells exhibited a hypersensitive response. Material embedded in resin and examined by light microscopy and transmission electron microscopy confirmed the location of hyphae between epidermal and hypodermal cells, and the presence of lipid bodies within the hyphae. In senescing needles, aggressive colonization of needle tissues occurred. Thus, for Lophodermium in white pine, endophytic infection is active rather than quiescent, and displays an alternate hyphal strategy to that seen in the reproductive phase.
No preview · Article · Aug 2001 · Mycological Research
[Show abstract][Hide abstract] ABSTRACT: The stomatal complex of eastern white pine (Pinus strobus L.) possesses a feature of uncertain function: the epistomatal chamber. The chambers are formed by the subsidiary cells that overarch the guard cells and are normally occluded with epicuticular wax. Morphologically distinct fungi resembling black yeasts are frequently observed within the epistomatal chambers submerged in the wax occlusions. Histochemistry shows that the fungal hyphae are viable and sheathed in a complex polysaccharide matrix. Experimental covering of the branches prevents colonization of the stomata, indicating that the inoculum originates exogenously. Preliminary investigations into the distribution of the fungus in Ontario, Canada, show an uneven distribution. Ecologically, the epistomatal chamber is proposed to be an ecotone between the phylloplane and the interior of the needle, one that possesses the survival advantages of both the phylloplane and the interior with few of the disadvantages associated with these two habitats. The presence of stomatal fungi may influence the response of host trees to aerial pollutants, may affect transpiration, and may prevent pathogen ingress.
No preview · Article · Jan 2001 · International Journal of Plant Sciences