Comparative anatomy and systematics of Catasetinae (Orchidaceae)

Catasetinae consist of five genera of pseudobulbous Orchidaceae of the Neotropics. Anatomy is characterized by sunken, three-celled foliar hairs, mostly tetracytic stomatal apparatuses, superficial stomata, homogeneous mesophyll, foliar fibre bundles, collateral vascular bundles in a single row, xylem and phloem sclerenchyma associated with vascular bundles in leaves, conical, and rough-surfaced silica bodies adjacent to vascular bundle sclerenchyma; epidermal cells of pseudobulbs with heavily thickened outer walls, pseudobulb ground tissue of assimilatory and water-storage cells, scattered vascular bundles in pseudobulbs, and sclerenchyma and stegmata associated only with phloem of pseudobulbs; roots with thin-walled velamen cells and tenuous spirals of cell wall material, distinctive epivelamen cells, thin-walled exodermal cells and vascular tissue embedded in parenchyma. Except for mucilaginous idioblasts that occur in Mormodes and Cycnoches , there are few outstanding anatomical differences among the five genera. Thus, there are few anatomical characteristics of phylogenetic value. The monophyly of Catasetinae is supported by the presence of sunken foliar hairs. Our results support a close relationship between Clowesia and Catasetum , and between Mormodes and Cycnoches. Among the outgroups Pteroglossaspis is especially distinctive.     

The leaf internal morphology and ultrastructure of Zostera muelleri irmisch ex aschers. (Zosteraceae): a comparative study of the intertidal and subtidal forms

The leaf anatomy, histochemistry and ultrastructure of the intertidal and subtidal seagrass Zostera muelleri Irmish ex Aschers. from Westernport Bay, Victoria were studied. Unusual anatomical and ultrastructural features are compared with other seagrasses and their functional significance is assessed. Subcuticular cavities are present in the young blade, but not observed in the older blade nor young and old leaf sheath. Wall ingrowths occur in the blade epidermal cells particularly on the inner tangential walls and the lower portions of the radial walls. Plasmodesmata are present between adjacent epidermal cells and between the epidermal and mesophyll cells, suggesting that solutes could transfer between these tissues both symplastically and apoplastically. Each leaf has three longitudinally aligned vascular bundles, each of which comprises a single xylem element isolated from the phloem tissue. The phloem consists of nacreous-walled sieve elements accompanied by phloem parenchyma cells which also process wall ingrowths. The xylem walls are completely hydrolysed and the middle lamella borders directly on the xylem lumen. Leaves have prominent air lacunae bisected transversely by septa at regular intervals along their length. Each septum consists of a file of small parenchyma cells with wall protuberances projecting into intercellular space. There are no major structural differences between the subtidal and intertidal plants, but the former have larger leaves and more leaves per shoot than the latter. In addition, a network of unusual reticulated fungal hyphae is present in the leaf intercellular spaces of the subtidal form and this network may facilitate solute transfer in these plants.     

柿树炭疽菌侵染寄主的细胞学研究*

超微结构研究表明,柿树炭疽菌(Colletotrichum gloeosporioides)侵染后在寄主细胞中形成初生菌丝和次生菌丝,寄主细胞膜外沉积了一层厚的电子不透明物质,初生菌丝与具有沉积物的寄主原生质膜之间有一层界面基质(interfacial matrix)。当初生菌丝扩张并侵染相邻细胞时, 围绕着初生菌丝层的界面基质消失,具有沉积物的原生质膜被逐步降解。初生菌丝在穿透寄主细胞壁过程中形成一个漏斗状的菌丝锥,然后穿透寄主细胞壁并迅速膨大, 然后形成厚壁的初生菌丝。初生菌丝在寄主细胞壁中收缩狭窄处产生一个隔膜,隔膜两边菌丝中细胞质的电子密度明显不同,菌丝锥中有浓密的电子密度。死体营养的次生菌丝在死的细胞中繁殖和扩展,并产生分枝。次生菌丝可直接穿透较薄的寄主细胞壁,无缢缩或任何变形现象,菌丝顶端部分未见隔膜产生;在穿透较厚的细胞壁时,靠近顶端处产生隔膜,顶端细胞膨大,使寄主细胞壁撕裂。接种90h后分生孢子盘在枝条表面形成。柿树炭疽菌其侵染过程有两个阶段,即初生菌丝的活体营养阶段和次生菌丝的死体营养阶段。     

DEVELOPMENTAL ANATOMY OF THE STEM OF WELFIA GEORGII,IRIARTEA GIGANTEA,AND OTHER ARBORESCENT PALMS: IMPLICATIONS FOR MECHANICAL SUPPORT

Changes in stem anatomy with radial position and height were studied for the arborescent palms Welfia georgii, Iriartea gigantea, Socratea durissima, Euterpe macrospadix, Prestoea decurrens, and Cryosophila albida. Vascular bundles are concentrated toward the stem periphery and peripheral bundles contain more fibers than central bundles. Expansion and cell wall thickening of fibers within vascular bundles continues throughout the life of a palm, even in the oldest tissue. Within individual vascular bundles, the fibers nearest the phloem expand first and fiber cell walls become heavily thickened. A front of expanding fibers moves outward from the phloem until all fibers within a vascular bundle are fully expanded and have thick cell walls. Peripheral vascular bundles differentiate first and inner bundles later. In the stem beneath the crown, vascular bundles and ground tissue cells show little or no size increase, but marked cell wall thickening during development for Welfia georgii. Beneath the crown, diameters of peripheral vascular bundles increase more than twofold for Iriartea gigantea, while diameters of central bundles do not increase. In Iriartea stems, ground tissue cells at the periphery elongate to accommodate expanding vascular bundles and cell walls become thickened to a lesser degree than in fibers; central ground tissue cells elongate markedly, but cell walls do not become thickened; and large lacunae form between central parenchyma cells. For Iriartea, Socratea, and Euterpe, sustained cell expansion results in limited, but significant increases in stem diameter. For all species, sustained cell wall thickening results in dramatic increases in stem stiffness and strength.     

Comparative anatomy and systematics of Senghas's cushion species of Maxillaria (Orchidaceae)

Using data obtained through anatomy and morphology, we used cladistics to examine the monophyly of Senghas's proposed classification of Maxillaria cushion plants and his placement of Mormolyca ringens. Trignidium obtusum was chosen as the outgroup. Leaves have multicellular hairs sunken in crypts, primarily anomocytic or primarily tetracytic stomatal apparatuses, homogeneous mesophyll, and scattered fibre bundles. Three types of adaxial hypodermis were observed: (1) water-storage cells, (2) fibre bundles scattered among water-storage cells, and (3) fibre bundles scattered among chlorenchymatous cells. Abaxial hypodermis of fibre bundles occurs in several Maxillaria species and in Trigonidium obtusum. At the midvein of the leaf, adaxial mesophyll cells of most species are anticlinally extended and empty, and the abaxial mesophyll is usually collenchymatous. Vascular bundles are collateral and usually in a single series. Pseudobulb epidermal cell walls are thin, or outer walls are thickened. Ground tissue consists of water-storage and assimilatory cells with vascular bundles and associated lacunae scattered throughout. Roots are velamentous and exodermal cell walls are usually n-thickened with tenuous bands of scalarifom thickenings on longitudinal walls. Tilosomes may be plaited, baculate, or spongy. Endodermal cell walls are usually U-thickened and pericycle cell walls are usually O-thickened opposite phloem sectors. Stegmata line the periphery of the thickened pericycle cells opposite phloem sectors in M. picta. Pith may be parenchymatous or sclerenchymatous. According to our phylogenetic analysis, Mormolyca ringens is consistently nested within the cladistic structure of Maxillaria. Therefore, Maxillaria likely is paraphyletic if Mormolyca ringens is recognized as generically distinct. It appears that Senghas's subgroup divisions of the unifoliate pseudobulbous maxillarias may also be artificial.     

Rumen bacterial degradation of forage cell walls investigated by electron microscopy

The association of rumen bacteria with specific leaf tissues of the forage grass Kentucky-31 tall fescue (Festuca arundinacea Schreb.) during in vitro degradation was investigated by transmission and scanning electron microscopy. Examination of degraded leaf cross-sections revealed differential rates of tissue degradation in that the cell walls of the mesophyll and pholem were degraded prior to those of the outer bundle sheath and epidermis. Rumen bacteria appeared to degrade the mesophyll, in some cases, and phloem without prior attachment to the plant cell walls. The degradation of bundle sheath and epidermal cell walls appeared to be preceded by attachment of bacteria to the plant cell wall. Ultrastructural features apparently involved in the adhesion of large cocci to plant cells were observed by transmission and scanning electron microscopy. The physical association between plant and rumen bacterial cells during degradation apparently varies with tissue types. Bacterial attachment, by extracellular features in some microorganisms, is required prior to degradation of the more resistant tissues.     

Developmental changes in cell wall structure of phloem fibres of the bamboo Dendrocalamus asper

BACKGROUND AND AIMS: Bamboo culms have excellent physical and mechanical properties, which mainly depend on their fibre content and anatomical structure. One of the features which is known to contribute to the high tensile strength in bamboo is the multilayered structure of the fibre cell wall. The aim of this study was to characterize the development of the layered structure in fibre cell walls of developing and maturing culms of Dendrocalamus asper. METHODS: Cell wall development patterns were investigated in phloem fibre caps of vascular bundles in the inner culm wall areas of Dendrocalamus asper of three different age classes (<6 months old, 1 year old, 3 years old). A combination of light microscopy and image analysis techniques were employed to measure cell wall thickness and to determine number of cell wall layers, as well as to describe the layering structure of fibre walls. Two-dimensional maps showing the distribution pattern of fibres according to the number of cell wall layers were produced. KEY RESULTS: The cell walls of fibres in phloem fibre caps located in the inner part of the culm wall of D. asper developed rapidly during the first year of growth. Six different fibre types could be distinguished based upon their cell wall layering and all were already present in the young, 1-year-old culm. In the mature stage (3 years of age) the multilayering was independent of the cell wall thickness and even the thinner-walled fibres could have a large number of wall layers. The multilayered nature of cell wall structure varied considerably between individual cells and was not exclusively related to the cell wall thickness. Nevertheless, fibres at the periphery of the fibre bundles and immediately adjacent to the phloem elements exhibited a consistent and high degree of layering in their cell walls. CONCLUSIONS: The multilayered structure of fibre cell walls was formed mainly during the first year of growth by the deposition of new wall layers of variable thickness, resulting in a high degree of heterogeneity in the layering patterns amongst individual fibres. A degree of 'order' in the distribution of multilayered fibres within the caps does exist, however, with multilayered cell walls common in fibres adjacent to phloem elements and around the edge of the fibre cap. These findings confirm the observations, primarily in Phyllostachys viridi-glaucescens. The layering structure was not found to be specifically related to the thickness of the cell wall.     

Effect of Rust Infection on Cell Walls of Barley and Wheat; Immunocytochemistry Using Anti-Barley Thionin as a Probe

Polyclonal antiserum prepared against barley cell wall thionin was used to localize and quantitate immunoreactive material on the cellular level in healthy and rust-infected leaves of barley and wheat. Three types of sites were used for the immunocytochemical analysis: as control sites, mesophyll cell walls were selected in uninoculated leaves, and in leaves that were inoculated with rust but where the sites were not in contact with the pathogen: these were compared with mesophyll cell walls that were in contact with intercellular rust hyphae in inoculated leaves.
Similar amounts of cell wall thionin were detected in all 3 barley cultivars before inoculation. At sites where intercellular hyphae of Puccinia hordei had made contact with mesophyll cell walls, less thionin was found in the compatible host cv. Larker, but in incompatible hosts (cvs. Gold and Bolivia) the thionin concentration did not differ from that of the controls.
Two cultivars of wheat were studied with respect to immunoreactive material in their mesophyll cell walls, the universal rust suscept cv. Little Club and the highly rust-resistant cv. Khapli. Before inoculation, leaves of cv. Khapli contained about twice the amount of immunoreactive material in mesophyll cell walls than those of cv. Little Club. This relation was unchanged in walls that had made contact with P. graminis tritici , but in non-contacted walls of infected cv. Little Club leavest, he concentration of this material had risen to levels typical for those of cv. Khapli. Tests for immunoreactive material with pre-embedding cytochemistry yielded negative results, indicating that it is not exposed on the surface of mesophyll walls in barley and wheat.     

Tubule bundle-inclusions in vacuoles of Tamarix aphylla L. mesophyll cells

Summary Vacuoles of differentiating mesophyll cells of Tamarix aphylla contain an amorphous electron-dense material in which stacks of parallel aligned striations are embedded. Cross-sections of the striations disclosed that they represent profiles of longitudinally sectioned bundles of tubules (tubule outer diameter 9.0 nm, tubule wall thickness 1.8 nm). In advanced mesophyll cell development, the amorphous vacuolar material disappears, whereas the bundles of tubules turn into bundles of double helices (double helix diameter 14.5 nm). Cytochemical treatment of mesophyll cells with the enzymes pepsin and trypsin has revealed that both the bundles of tubules/double helices and the embedding material are constituted of protein. The possible functional role of the vacuolar inclusions is discussed.     

Rumen bacterial interrelationships with plant tissue during degradation revealed by transmission electron microscopy

The mode of rumen bacterial degradation of cell walls in coastal bermudagrass [Cynodon dactylon (L) Pers.] differed with the plant tissue type. Bacteria degraded thin, primary cell walls of mesophyll and phloem apparently by extracellular enzymes and without prior attachment; thick-walled bundle sheath and epidermal cells apparently were degraded after bacterial attachment, in some types by an extracellular substance, to the plant cell walls. Rumen bacteria split the nondegraded cuticle from the epidermis by preferentially attacking the cell just underneath the cuticle. The propensity for bacterial attachment to lignified cells of the vascular tissue was low, and bacterial degradation of these cells did not occur after 72 h of incubation.     

Comparative vegetative anatomy of Stanhopeinae (Orchidaceae)

Stanhopeinae are a group of tropical American orchids characterized by euglossine bee pollination and lateral inflorescences stemming from the bases of pseudobulbs. Leaves are hypostomatal, and all stomatal configurations are tetracytic. Chlorenchyma is homogeneous and characterized by fibre bundles in adaxial/abaxial or adaxial/median/abaxial positions. Collateral vascular bundles occur in a single row and feature phloic and xylic sclerenchymatous caps and thin-walled bundle sheath cells. Fibre bundles and vascular sclerenchyma are accompanied by stegmata containing conical silica bodies. Pseudobulbs have thick-walled turbinate epidermal cells and ground tissue of smaller, living assimilatory cells and larger, dead water-storage cells. Fibre bundles are usually absent but occur in several genera. Collateral vascular bundles show phloic sclerenchyma, but xylic sclerenchyma occurs only in die larger vascular bundles. Phloic and xylic sclerenchyma are associated with stegmata containing conical silica bodies. Roots are velamentous. Velamen cell walls have fine, spiral thickenings. Exodermal cells are thin-walled. The cortex features scattered thick-walled cells and in some cases branched bars of secondary cell wall material. Endodermis is either u-or O-thickened, but pericycle is always O-thickened opposite the phloem. Vascular tissue consists of alternating strands of xylem and phloem surrounded by a matrix of thick-walled cells. Pith cells may be parenchymatous or sclerenchymatous.     

Infection of Onion by the White Rot Pathogen, Sclerotium cepivorum

Infection of onion tissue by Sclerotium cepivorum occurred from germ tubes penetrating between adjacent epidermal cell walls or directly, via penetration pegs produced from slightly swollen hyphal tips or from beneath dome shaped infection cushions. After passing through the cuticle, the infection peg enlarged to form an infection hypha within the primary cell wall. Extensive degradation of the epidermal cell wall occurred, often at a distance of 2–3 cells from the advancing hyphae. As infection advanced, hyphae spread rapidly from the epidermis to the cortex growing between and within dead/dying host cells. Extensive host cell death resulted in localized collapse of the tissue around infection points. Complete colonization of the internal tissues of the root and stem base occurred within 5–7 days of inoculation.     

Comparative vegetative anatomy and systematics of Vanilla (Orchidaceae)

Vanilla is a pantropical genus of green-stemmed vines bearing clasping (aerial) and absorbing (terrestrial) roots. Most vanillas bear normal, thick foliage leaves; others produce fugacious bracts. Seventeen species, including both types were studied. Foliage leaves of Vanilla are glabrous, have abaxial, tetracytic stomatal apparatuses, and a homogeneous mesophyll. Species may or may not have a uniseriate hypodermis. Crystals occur in the foliar epidermises of some species, but all species have crystalliferous idioblasts with raphides in the mesophyll. Vascular bundles in leaves are collateral and occur in a single series alternating large and small. Sclerenchyma may or may not be associated with the vascular bundles. Scale leaves may be crescent or C-shaped and usually have abaxial stomatal apparatuses. A hypodermis may or may not be present; the mesophyll contains raphide bundles in idioblasts. Vascular bundles are collateral and occur in a single row sometimes aligned close to the adaxial surface. They may or may not be associated with sclerenchyma. Stems of leafy vanillas show a sclerenchyma band separating cortex from ground tissue; stems of leafless vanillas do not show a sclerenchyma band. Ground tissue of the stem may consist solely of assimilatory cells or mixed assimilatory and water-storage cells. In some species centrally located assimilatory cells are surrounded by layers of water-storage cells. A uniseriate hypodermis is present in all stems. Sclerenchyma may completely surround the scattered collateral vascular bundles, occur only on the phloem side, or be absent. Both aerial and terrestrial roots are notable for their uniseriate velamen the cell walls of which may be unmarked or ornamented with anticlinal strips. Exodermis is uniseriate; the cells vary from barely thickened to strongly thickened. Only the outer and radial walls are thickened. Cortical cells of aerial roots generally have chloroplasts that are lacking from the same tissue of terrestrial roots. Raphide bundles occur in thin-walled cortical idioblasts. Endodermis and pericycle are uniseriate; pericycle cells are all ?-thickened opposite the phloem. Cells of the endodermis are either ?- or ∪-thickened opposite the phloem. Vascular tissue may be embedded in thin- or thick-walled sclerenchyma or in parenchyma. Metaxylem cells are always wider in terrestrial than in aerial roots of the same species. Pith cells are generally parenchymatous but sclerotic in a few species.     

种衣剂17号包衣对小麦条锈菌发育影响的超微结构研究

本研究采用电镜技术研究了种衣剂17号对小麦条锈菌发育的影响。观察结果表明,该种衣剂引起病菌和寄主细胞内发生了一系列变化。病菌菌丝和吸器内脂肪粒和液泡明显增加;菌丝壁和吸器壁呈不规则加厚;菌丝分枝处无隔膜产生或隔膜畸形;有的吸器母细胞产生的畸形入侵栓,大都不能穿透寄主细胞壁,初生吸器外间质内沉积有染色较深的物质,次生吸器可产生多个不规则分枝,但不能扩张膨大;菌丝外渗的物质可能引起寄主细胞的坏死;大多数受侵寄主细胞可分泌形成较大的胼胝质,有时寄主细胞分泌的物质可将吸器体完全包围起来。上述结果表明,种衣剂17号不仅可直接作用于条锈菌,而且也可通过影响寄主而间接地影响病菌。     

Development of thallus axes in Usnea longissima (Parmeliaceae, Ascomycota), a fruticose lichen showing diffuse growth

? Premise of the study: While cell wall thickening in plants is generally associated with tissue maturation, fungal tissues in at least two lichens continue to grow extensively while accumulating massively thickened cell walls. We examined Usnea longissima to determine how diffuse growth shapes morphological and anatomical development of thallus axes and how the highly thickened cell walls of the central cord behave in diffuse growth. ? Methods: Fresh material was examined with light and epifluorescence microscopy and conventional and low-temperature SEM. Fixed material was embedded in Spurr's resin, microtome-sectioned, and examined with TEM and light microscopy. ? Key results: Main axes consisted essentially of bare medullary cord tissue; their characteristic morphology developed by destruction of the overlying cortex and consequent stimulation of lateral branch formation. Fungal cells of the cord tissue continually deposited wall layers of electron-transparent substances and layered, electron-dense materials that include UV-epifluorescent components. Discontinuities were evident in the outermost layers; new branch cells grew through wall materials accumulated by older neighboring cells. ? Conclusions: Sustained diffuse growth of cord tissue in U. longissima underlies the structural transformation of a corticated thallus branch into a long axis. In the cord tissue, diffuse growth may be responsible for the increasingly disrupted appearance of the older, electron-dense cell wall layers, while new wall materials are laid down adjacent to the protoplast. Cell and tissue development appeared comparable to that observed previously in Ramalina menziesii, although accumulation of wall material was somewhat less extensive and with a greater proportion of electron-dense/UV-epifluorescent components.     

The Effects of the Harmful Gases SO2 and HF on plant Leaf Structure

As the injury induced by S02 appears progressively, the cells contracted and became deformed, the protoplasm and the chloroplasts turned yellow-brown or collapsed while no effects were seen in the vascular bundles generally. Howewr, as the injury induced by HF appears progressively, the cells were not deformed immediately, the protoplasm became red-brown, the mesophyll cells adjacent to stomata or vascular bundles became red-brown too, there were no effects on chloroplasts, which did not collapse until the tissue necrosis appeared, the cells of xylem and phloem turned red-brown. The process of the injury to leaf structure induced by SO2 is discussed. It is observed that destruction of chlorophyll and the interruption of photosynthesis by SO2 took place first in the palisade tissue, whereas the contraction and disintegration of the cells first in the spongy tissue. The effect of HF to the contractive collapse of chlorophyll and mesophyll occurred after the influence on protoplasm appeared.     

Cytopathologie von viroid-infiziertem Pflanzengewebe

Cytopathology of viroid-infected plant tissue II. Light- and electron microscopical investigations on the leaf tissue of the Chrysanthemum morifolium cultivar “Mistletoe” after infection with the chrysanthemum stunt viroid (CSV) The infection of the Chrysanthemum morifolium cultivar “Mistletoe” with the chrysanthemum stunt viroid (CSV) leads to the appearance of numerous yellowish leaf spots 2–5 mm in diameter. The cells of these chlorotic leaf areas were investigated by phase contrast- and electron microscopy and compared with the cells of the adjacent green tissue and the tissue of healthy plants. Phase contrast microscopy showed that the chlorotic tissue containes about 50 % more cells per area and that their size is reduced by 30–60 %. The parenchymatic cells of the xylem and phloem are irregular and their walls are malformed. In these cells the chloroplasts are reduced to about half in their size and number. In the electron microscope an accumulation of osmiophilic material between the thylakoid membranes of the chloroplasts of the chlorotic cells and a deterioration of the chloroplast stroma can be observed. Moreover, malformations of the cell wall and in the cell wall-associated plasmalemma-somes are found, which lead to an increase in contrast and to irregularities of their surface and internal structure. The most prominent CSV-specific cytopathic effect in cells of the vascular tissue is the extreme accumulation of microfilament bundles which were analysed in detail with the aid of a goniometer. The observed viroid-induced ultrastructural changes are compared with previously described changes caused by conventional plant viruses and the possible functional implications are discussed.     

冠盘二胞Marssonina coronaria侵染不同抗性苹果叶片的组织病理学研究

利用光学和电子显微镜,从组织细胞学水平系统研究了冠盘二胞Marssonina coronaria在苹果抗、感病品种叶片上的侵染过程及侵染后寄主细胞的超微结构特征。结果表明：冠盘二胞的侵入和定殖过程可以分为6个阶段：孢子萌发与芽管形成、附着胞形成、侵入细胞角质层、在叶肉细胞内产生吸器、菌丝在叶肉细胞间和细胞内扩展、分生孢子盘形成。随着菌丝扩展,受侵寄主细胞出现细胞壁加厚,细胞壁降解,质壁分离,叶绿体内淀粉粒、嗜饿颗粒积累,叶绿体基粒片层瓦解,线粒体空泡化等现象。在不同抗性的苹果品种上,分生孢子萌发率差别不明     

Cytological Study of Wheat Spike Infection by Bipolaris sorokiniana

The infection of wheat spikelets by Bipolaris sorokiniana , the causal agent of black point on grains and grain shrivelling, was examined by light and electron microscopy. Conidia of the pathogen germinated 6–12 h after inoculation on the surfaces of the different spike tissues. Extracellular sheaths were observed on germ tubes and appressoria attached to the surfaces of lemma, palea and seeds, but were only scarcely detected on the surface of conidia. Appressoria, frequently found over grooves, formed penetration hyphae invading the epidermal cell walls. Infection process was similar on the surface of the lemma, palea and glume. Growth of the fungus in the epidermal and parenchyma cells was found predominantly in the cell walls, and hyphae also extended intercellularly and intracellularly. Infection of seeds appeared to occur via two ways: (i) direct infection of the outer layers of the cell walls of the pericarp and (ii) through entering the stigma into the pericarp cells. Secretion of host cell wall hydrolytic enzymes at the apex of the penetrating hyphae may facilitate the spread of the fungus. In addition, toxins secreted by the fungus might explain the rapid death of host cells in contact with or distant to fungal cells. A host response to fungal infection involved the development of appositions between cell wall and plasma membrane in cells adjacent to fungal cells. Fungal hyphae were sometimes also surrounded by electron dense material.     

Melanin Production by a Filamentous Soil Fungus in Response to Copper and Localization of Copper Sulfide by Sulfide-Silver Staining

Gaeumannomyces graminis var. graminis, a filamentous soil ascomycete, exhibited enhanced cell wall melanin accumulation when exposed to as little as 0.01 mM CuSO(inf4) in minimal broth culture. Because its synthesis was inhibited by tricyclazole, the melanin produced in response to copper was dihydroxynaphthalene melanin. An additional hyphal cell wall layer was visualized by electron microscopy when hyphae were grown in the presence of copper and fixed by cryotechniques. This electron-dense layer was between the outer cell wall and the inner chitin layer and doubled the total wall thickness. In copper-grown cells that were also treated with tricyclazole, this electron-dense layer was absent. Atomic absorption spectroscopy demonstrated that up to 3.5 mg of Cu per g of fungal mycelium was adsorbed or taken up by hyphae grown in 0.06 mM CuSO(inf4). A method for silver enhancement was developed to determine the cellular location of CuS. CuS was present in cell walls and septa of copper-grown hyphae. Electron microscopy of silver-stained cells suggested that CuS was associated with the melanin layer of cell walls.