Ultrastructure at the Host-Parasite Interface of Phytophthora capsici in Roots and Stems of Capsicum annuum

The infecting hyphae of Phytophthora capsici grew intercellularly in infected tissues of roots and stems of pepper (Capsicum annuum). The vascular tissues were not markedly disorganized even when heavily infected. Intercellularly growing hyphae penetrated the host cells by forming haustorium-like bodies. The consistent features of ultrastructural changes in infected tissues of pepper roots and stems were degeneration of cell organelles and dissolution of host cell walls. The cytoplasm detached from the cell wall aggregated abundantly around some haustorium-like bodies or the penetration sites of fungal hyphae. The host cell walls were palely stained, thinned and swollen, possibly being biochemically altered by the action of fungal macerating enzymes. Electron-dense, wall-like material was apposed on the outer wall of xylem vessel contacted by fungal hyphae. The infecting hyphae were also surrounded by granular, dark-staining cytoplasm. Characteristics of host cell responses to the invading P. capsici were the deposition of papilla-like material on host cell walls next to hyphae and the encasement of haustorium-like bodies with wall appositions.     

Concentric Bodies in a Parasitic Fungus of Malva sylvestris (Malvaceae) Pollen

Ultrastructural examinations revealed concentric bodies in hyphae of a parasitic ascomycete, infecting pollen of Malva sylvestris ssp. mauritiana . These structures consist of three concentric zones and are similar to those found in mycobionts of several lichens and only a few nonlichenized ascomycetes. Typical septal pores of ascomycete hyphae were present, usually plugged by electron-dense material and associated with one or more Woronin bodies.     

Structural aspects of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] tuberculate ectomycorrhizae

Summary Tubercles of Pseudotsuga menziesii consisted of clusters of ectomycorrhizae surrounded by a peridiumlike rind. Energy dispersive spectroscopy demonstrated that crystals found in the zone of loose hyphae extending from the inner rind to the mantle of each root probably contain calcium oxalate. Inner mantle and Hartig net hyphae showed a labyrinthine branching pattern and stored carbohydrates and protein. The Hartig net formed up to inner cortical cells which had thickened, darkly stained walls. Bacteria were located either along with hyphae within the rind or as colonies on the surface of the tubercle.     

Ultrastructure of Fomes igniarius mycelium

The mycelium is composed of thin-walled hyphae, fiber hyphae and cuticular cells, the modified cells developing from the thin-walled hyphae with a dolipore septum at the differentiation point. The cell wall is usually triplelayered. occasionally, multilayered. Cell organelles such as endoplasmic reticulum, mitochondria and vesicles are found in abundance in thin-walled hyphae. Characteristic features of this fungus are the concentric membrane systems from which vesicles arise, the membrane-enclosed osmophilic bodies in vacuoles and the dense bodies in the cytoplasm. As the fiber hyphae and cuticular cells develop, the innermost layer of the wall thickens and the cell contents become disorganized so that, at the maturity of these cells, there is a reduced amount of diffuse cytoplasm, or none in the lumen.The study formed part of a doctoral dissertation submitted by the author to the University of Alberta, Edmonton, Alberta, Canada, 1971.     

Ultrastructural characterisation of the host–pathogen interface in white blister-infected Arabidopsis leaves

In this study transmission electron microscopy (TEM) was used to examine details of the host–pathogen interface in Arabidopsis thaliana cotyledons infected by Albugo candida, causal agent of white blister. After successful entry through stomatal pores, the pathogen developed a substomatal vesicle and subsequently produced intercellular hyphae. TEM observations revealed that coenocytic intercellular hyphae ramified and spread intercellularly throughout the host tissue forming several haustoria in host mesophyll cells. Intracellular haustoria were spherical and 4.5 μm in diameter. Each haustorium was connected to intercellular hyphae by a narrow, slender haustorium neck. The cytoplasm of the haustorium included the organelles characteristic of the pathogen. No obvious response was observed in host cells following formation of haustoria. Most of the mesophyll cells contained normal haustoria and the host cytoplasm displayed a high degree of structural integrity. Absence of host cell wall alteration and cell death in penetrated host cells suggest that the pathogen exerts considerable control over basic cellular processes and in this respect, response to this biotrophic Oomycete differs considerably from responses to other pathogens such as necrotrophs. Modification of the host plasma membrane (PM) along the cell wall and around the haustoria, was detected by applying the periodic acid-chromic acid-phosphotungstic acid (PACP) staining technique. After staining with PACP, the host PM was found to be intensely electron dense where it was adjacent to the host cell wall and the distal region of the haustorial neck. By contrast, the extrahaustorial membrane, where the host PM surrounded the haustorium, was consistently very lightly stained.     

铁皮石斛组培苗与菌根真菌共培养过程中的相互作用

由于人为的滥采滥挖和野外生境的退化, 使得铁皮石斛 (Dendrobium officinale) 这种名贵的中药材一直处于极度濒危的状态。为了从菌根真菌的角度给人工保育铁皮石斛提供理论指导, 对铁皮石斛的组织培养苗人工接种‘GDB181’菌株 (Epulorhiza sp.) 。培养60d后, 接菌苗平均鲜重增长率比对照苗高出了84.8%。在营养元素含量方面, 接菌苗的B、Si、Fe、Cu和Mn元素含量的净增率分别为780%、533%、192%、191%和128%, 均在100%以上;其他元素含量也有不同程度的增加 (除Zn外), 结果证明两者有效地建立了共生关系。在显微和超微结构的观察中发现:真菌菌丝随机破坏铁皮石斛的根被入侵到外皮层, 并从外皮层细胞不断扩展延伸到皮层的大型细胞, 最后在大型细胞中被分解消化。在真菌侵染过程中, 被侵染的皮层细胞的细胞壁严重扭曲变形, 菌丝在皮层细胞形成菌丝结, 菌丝结常位于细胞核附近或包围细胞核。在皮层的大型细胞中, 菌丝细胞被植物的溶酶体包围, 部分或全部被消解, 出现脱壁或失去细胞质甚至成为空腔等变化, 最终形成衰败的菌丝残骸, 溶酶体也随之消失。溶酶体分布越多的部位, 菌丝细胞消解变形越严重。含有菌丝残骸的皮层细胞可被新侵染的菌丝重新定殖, 这一菌丝侵染被消化再侵染的过程在铁皮石斛生长发育过程中可不断重复发生。     

Phoma (Peyronellaea) as zoopathogen.

Two case reports add to the rare recorded instances of infection of man and other animals by Phoma or Phoma-like molds. Phoma cava was consistently cultured from aural dermatitis of a white-tailed deer (Odocoileus virginianus), and tissue sections of the ear revealed fragments of apparent pycnidial walls, as well as many septate hyphae. In the second instance, numerous Phoma-like pycnidia occurred in and upon the hairs of a young child, in a lesion initiated by Trichophyton infection.     

Electron microscopy of the endophyte ofAlnus glutinosa

Earlier light microscopic investigations have revealed that the endophyte ofAlnus glutinosa presents itself in three different forms. In the present study this is confirmed by electron microscopy; also, new data on the cytology of the endophyte have been obtained.The host cells are primarily infected by the hyphal form of the endophyte. A plant cell nucleus and mitochondria can be found in the infected host cells.In the majority of the infected cells, so-called vesicles develop at the tips of the hyphae. Electron micrographs show that these vesicles, as well as the hyphae, are surrounded by the host-cell cytoplasmic membrane. The endophyte cytoplasm inside the vesicles is divided in all directions by cross walls, many of which are incomplete. Plasmalemmosomes are conspicuous. Some vesicles look vigorous but others shrunken or nearly devoid of cytoplasm as if being digested.A minority of host cells situated between the vesicle-containing ones are completely filled by bacteria-like cells. These host cells, in contrast to the other ones, do not contain a nucleus nor mitochondria, nor are the endophyte cells in them enveloped by a host cell cytoplasmic membrane: these host cells are dead. Vesicles are not found in these cells.It is inferred that a living host cell exerts a stimulus on the endophyte to which the latter responds by forming vesicles at the tips of the hyphae. At a later stage the host cells digest the vesicles and the hyphae. On the other hand, if a host cell does not survive the infection, the hyphae divide into bacteria-like cells, which are not digested owing to the absence of host cytoplasm.According to the cytology of the hyphae, the endophyte is an actinomycete.The cytology of the endophyte needs further elucidation. Its plasmalemmosomes, or membranous bodies connected with the cytoplasmic membrane, are beautifully developed. The striated bodies described on p. 359 under 4) may be a new feature, which may turn up in other actinomycetes or bacteria.     

Electron microscopy of vesicular-arbuscular mycorrhizae of yellow poplar. II. Intracellular hyphae and vesicles.

Intracellular hyphae and vesicles in mycorrhizal roots of yellow poplar were examined by electron microscopy. An investing layer of host wall material and cytoplasm enclosed the endophyte within the cells. Young developing hyphae contained abundant cytoplasm and few vacuoles. As hyphae matured, they became highly vacuolated and accumulated carbohydrate (glycogen) and lipid reserves. Mature vesicles were engorged with lipid droplets, possessed a trilaminate wall and were also enclosed by host wall material and cytoplasm. Compared with uninfected cells, infected cortical cells showed an increase in cytoplasmic volume, enlarged nuclei, and a reduction of starch reserves. Host nuclei were always proximal to the hyphae during hyphal development and deterioration. While other cytoplasmic components of infected and uninfected cells were comparable large electron-dense bodies occurred in vacuoles of most cells containing hyphae. Deterioration of intracellular hyphae occurred throughout the samples examined. Septa separated functional and degenerating portions of the hyphae. Hyphal deterioration involved degeneration and ultimate disappearance of fungal cytoplasm as well as collapse of hyphal walls. Based on these observations, the authors hypothesize that deterioration of the endophyte may release significant quantities of mineral nutrients, via hyphal contents, which are absorbed by the host.     

Electron microscope studies on Tomentella

Summary Tomentella bombycina andT. fuscoferruginosa were examined by routine techniques of light and electron microscopy. Special attention was paid to the ultrastructure and inter-relationships of the generative subicular hyphae and subhymenial hyphae. The cell wall consisted of three layers in the generative subicular hyphae and only one layer in the subhymenial hyphae; this corresponded to the inner layer of the first and originated from it. Cells with two nuclei, normal mitochondria, large vacuoles, sparse endoplasmic reticulum and lomasomes were observed. Sometimes the nuclear membrane had unusually large pores and larger open gaps extending over 1/4 of the circumference. Septa with central dolipore-type pores were present. Clamp connections were not frequent. Finally, certain cells of the subhymenial hyphae appeared full of globular material, presumably lipids.     

The infection process ofFusarium oxysporum in cotton root tips

Summary Conidia ofFusarium oxysporum f. sp.vasinfectum started to germinate on the roots of cotton (Gossypium barbadense L.) 6 h after inoculation and formed a compact mycelium covering the root surface. 18 h later, penetration hyphae branched off and infected the root. The number of penetration hyphae increased with the number of conidia used for inoculation. The optimal temperature for penetration was between 28 and 30 °C. The highest numbers of penetration hyphae were found in the meristematic zone, 40 percent less in the elongation and root hair zones, and none in the lateral root zone. The fine structure of the infection process was studied in protodermal cells of the meristematic zone and in rhizodermal cells of the elongation zone. The penetration hyphae were well preserved after freeze substitution and showed a Golgi equivalent consisting of three populations of smooth cisternae. Plant reactions were found already during fungal growth on the root surface. In the meristematic zone, a thickening of the plant cell wall due to an apposition of dark and lightly staining material below the hyphae occurred. This wall apposition increased in size around the hypha invading the plant cell and led to the formation of a prominent wall apposition with finger-like projections into the host cytoplasm. In the elongation zone, the deposits around the penetration hypha appeared less thick and the dark inclusions were less pronounced. High pressure freezing of infected cells revealed, thatF. oxysporum penetrates and grows within the host cells without inducing damages such as plasmolysis, cell degeneration or even host necrosis. We suggest thatF. oxysporum has an endophytic or biotrophic phase during colonization of the root tips.Abbreviation Ph penetration hyphae     

Microampullary organs of a freshwater eel-tailed catfish,Plotosus (tandanus) tandanus

Whole body studies of Plotosus tandanus revealed that ampullary pores occur over the entire body of the fish, but are in higher concentrations in the head region. These pores give rise to a short canal (50-60 microm) produced by columnar epithelial cells bound together by tight junctions and desmosomes. At the junction of the canal and the ampulla, cuboidal epithelial cells make up the wall. The ampulla consists of layers of collagen fibers that surround flattened epithelial cells in the lateral regions and give rise to supportive cells that encase a small number of receptor cells (10-15). The ampullary wall comprises several types of cells that are adjoined via tight junctions and desmosomes between cell types. The ovoid receptor cells possess microvilli along the luminar apical area. Beneath this area, the cells are rich in mitochondria and rough endoplasmic reticulum. An unmyelinated neuron adjoins with each receptor cell opposite multiple presynaptic bodies. This form of microampulla has not been previously described within the Family Plotosidae.     

The ultrastructure of septal pores and associated structures in the ascogenous hyphae and asci ofSordaria humana

Summary Septal pores and associated structures have been studied in ascogenous hyphae, croziers and asci ofSordaria humana by means of electron microscopy of serial and random sections. Pores exhibit variable structures from relatively simple pore caps to complex swollen rims with associated membrane cisternae. The simple types are found at the base of the ascogenous hyphae while the complex forms occur at the apex, in the croziers and in very young, presporulation asci. Post-sporulation asci contain a relatively simple type of pore structure. Cells which subtend the ascogenous hyphae exhibit both open and capped pores in their cross walls. Pore structures may be asymmetric in which case they show greater complexity on the side of the cross wall nearest to the apex or crozier. Membranous components of the complex pores are continuous with the endomembrane systems of the two adjacent cells and thus with the outer membranes of the nuclear envelopes. Membrane continuities may connect prefusion nuclei or fusion nuclei in penultimate cells, with nuclei of the stalk and terminal cells of croziers. Some speculation is presented as to the implication and possible roles of these structures in relation to cell differentiation within the ascogenous hyphae and croziers.     

墨兰菌根的结构及酸性磷酸酶定位研究

利用光学显微镜、电子显微镜及细胞化学方法,对墨兰菌根的结构和酸性磷酸酶定位进行了初步研究。结果表明墨兰具有典型的兰科植物根结构,发现该兰花的根的外皮层不具薄壁通道细胞,菌根真菌通过破坏部分根被和外皮层细胞而侵入根的皮层细胞并在细胞内形成菌丝结,侵入的菌丝被染菌皮层细胞质膜和电子透明物质包围,进一步被消化并聚集成衰败菌丝团块。酸性磷酸酶在染菌皮层细胞及包围菌丝的皮层细胞质膜和衰败菌丝细胞壁上有强烈的酶反应,衰败菌丝周围分布有许多单层膜的含酶小泡,它们可相互愈合形成大的含酶泡或与包围菌丝的质膜融合,类似于兰科植物共生原球茎中观察到的现象。说明皮层细胞可主动释放水解酶参与对菌丝的消化     

Differential cytoplasm-plasma membrane-cell wall adhesion patterns and their relationships to hyphal tip growth and organelle motility

Summary Plasmolysis of hyphae of the oomycetesSaprolegnia ferax andAchlya ambisexualis and the ascomyceteNeurospora crassa produced abundant cytoplasmic strands between the retracted cytoplasm and punctate adhesions of the plasma membrane to the cell wall. These strands formed throughout the length of mature hyphae and are the first demonstration of Hechtian strands in hyphae. In contrast to similar strands in various plant cells, the strands inSaprolegnia lacked endoplasmic reticulum but contained F-actin, suggesting similarity between their adhesion sites and focal contacts in animal cells. However, strand adhesion to the wall was insensitive to RGD-containing peptides, suggesting that the trans-membrane adhesion molecules differ from animal integrins. The pattern of plasma membrane-cell wall adhesion varied in different zones along hyphae, with broad, irregular connections in the extreme apex, uniform and continuous connection in a transition zone, and small, punctate adhesions in the mature subapical zone, suggesting differential functions in these different regions. The apical adhesions are important in tip growth, as diverse inhibitors induced concomitant changes in hyphal growth and the adhesions in the apical and transition zones. Plasmolysis also induced cytoplasmic migrations throughout hyphae. Such migrations were dominated by the central cytoplasm, and produced distorted organelles which spanned central and peripheral cytoplasm, thus supporting the idea that the adhesions in mature zones of hyphae anchor the peripheral cytoplasm and facilitate cytoplasmic and organelle migrations.Abbreviations OM organic medium - RP rhodamine phalloidin - DIC differential interference contrast - PIPES piperazine-N,N-bis-2-ethanosulphonic acid     

Hyphal structure in Fusarium oxysporum (Schlecht) revealed by freeze-etching

Summary Freeze-etched hyphae of F. oxysporum exhibited a single layered cell wall; a plasmalemma, in which invaginations were frequently associated with paramural vesicles; cytoplasma bearing lipid droplets, vacuoles, intravacuolar vesicles and nuclei with typical nuclear pores. Some hyphae bore crystalline inclusions characterized by a pronounced hexagonal, external ornamentation and it is suggested that the presence of these crystals and intravacuolar vesicles are indicative of aging hyphae.     

Ultrastructure and Development of Sclerotia of Botrytis cinerea Pers. in vitro

The development of sclerotia of Botrytis cinerea was examined at four stages during their maturation. The surface structure developed a network of profusely branched hyphae through their coalescence to a compact sclerotial body which was maturated by the deposition of melanin pigment. A characteristic feature of the hyphal cells of B. cinerea during the later stages of development was the presence of paramural bodies (plasmalemmasomes and lomasomes). Electrondense bodies with a limiting double-membrane congregated against the transverse septa of hyphal cells as sclerotia matured and may migrate from cell to cell through septal pores. We suggest that these and the lipid bodies found in hyphal cells may have a storage function in the resting sclerotia.     

Cytological studies on rust fungi. (vi) fine structures of infection process of Kuehneola japonica (diet.) dietel

The behavior of rust fungi in their host plants has been elucidated by electron microscopy. However, most of the ultrastructural studies on rust fungi have focused on the uredial stage. In order to elucidate the features of the sporidial stage, we studied the fine structure of Kuehneola japonica, a short-cycle rust, in rose leaves. Infection pegs arising from appressoria penetrated the host walls. Papillae formed at the time of penetration against the outer epidermal cell walls. The papillae which had formed at the penetration sites grew extensively and partially surrounded the intracellular hyphae which were connected with the infection pegs. The intracellular hyphae in the epidermal cells developed further and entered adjacent parenchyma cells. Walls of parenchyma cells either invaginated or thin papillae formed at penetration sites and the invaginated walls or papillae surrounded the necks of the intracellular hyphae. Intracellular hyphae in both epidermal and parenchyma cells were not enveloped by the sheath before 20 days after inoculation. In specimens prepared 20 days after inoculation, some of the intracellular hyphae were enveloped by a sheath in both palisade and spongy parenchyma cells. The sheathed hyphae resembled haustoria of other rust fungi which had been described previously. Teliospore initials were formed in mycelial masses in intercellular spaces between the epidermal cells and palisade parenchyma cells 20 days after inoculation. Uninucleate teliospores developed from teliospore initials 30 days after inoculation.Contribution No. 32.     

Aspects of the dimorphism of Histoplasma farciminosum: a light and electron microscopic study.

Within 48h following the induction of mycelial to yeast-like phase conversion of Histoplasma farcininosum, randomly occurring hyphal cells were observed to contain multiple nuclei and markedly increased numbers of mitochondria. Yeast-like cells arose as buds from swollen tips of terminal hyphae, as sessile buds along the hyphae, and as buds from chlamydospores. Yeast-like cells were characterized by the presence of numerous buds over the surface of the mother cell. Bud scars were evident in the cell wall of the mother cell following abscission of the bud cell. Little similarity was noted between the fine structure of yeast-like H. farciminosum and that reported for H. capsulatum. The yeast-like cells of H. frciminosum underwent rapid transformation to the mycelial phase at 25 degrees C. The hyphal cell wall originated from the inner layer of cell wall of the yeast-like form. The cytoplasm of the hyphal cell usually contained a single nucleus, scattered mitochondria and occasional lipid storage bodies. Occasionally, Woronin bodies were observed at the septal pore.     

THE MEMBRANE SYSTEM OF STREPTOMYCES CINNAMONENSIS

The plasma membrane bounding the cytoplasm immediately inside the hyphal wall of Streptomyces cinnamonensis may not retract from the hyphal wall. When it does retract from the wall, it appears as a single dark line in some sections and as 2 dark lines separated by a light zone in others. The membrane system consists of mesosomes and endomembrane structures. The mesosomes are those membrane structures whose derivatives appear to be the plasma membrane. The endomembrane structures, in the present report, are those that appear to have been derived from either the cytoplasm or the limiting membranes of the pre-existing membrane structures. All membranes seem capable of proliferation, a mechanism obviously responsible for the growth of the individual membrane structures and for the origin of many new ones. The mesosomes, according to their limits, are of 2 distinct types, the open mesosomes and the closed mesosomes. The open mesosomes are partially enclosed by limiting membranes, leaving the unenclosed sides limited by the wall. These mesosomes, when old, usually in aerial hyphae, may become attached to the wall and somewhat deleted from their limiting membranes. The individual membranes in their interior may appear disfigured. The closed mesosomes are completely surrounded by the limiting membranes. These mesosomes, as well as endomembrane structures, retain their original positions in the cytoplasm even in the older aerial hyphae, and the membranes in their interior usually remain practically as distinct in the aerial hyphae as they are in the substratal hyphae. New mesosomes and endomembrane structures are being formed continuously as the mycelium develops. The mesosomes, as a rule, occupy more or less the peripheral regions of the cytoplasm, while the endomembrane structures distribute themselves widely in the cytoplasm and also in the nucleoids. The appearance of the unit membranes, being double-layered (2 dark lines separated by a light line), is not consistent. The membranes as a whole are more resistant to degeneration than the cytoplasm and the nucleoids.