Fine structure of the extracellular sheath and cell walls inOphiostoma novo-ulmigrowing on various substrates

Abstract

The presence of microfilamentous-like structures of tubular appearance (MFS) in cell walls and extracellular sheath material (ES) in a number of isolates of Ophiostoma novo-ulmi Brasier grown on various substrates and following various treatments is reported. Standard fixation or high-pressure freezing methods were used, and cytochemical tests were carried out to detect fungal and host wall components and, in some cases, fungal DNA. In some cases, serial 0.2-µm-thick sections were examined at 120 kV and tilted to obtain stereoscopic images. Whether the fungal cell walls were thick and composed of an outer opaque and inner more electron-lucent layers, or thin and barely perceptible, MFS were observed to extend from the cell cytoplasm as parallel structures across the walls into the surrounding medium, including host cell components in infected elm tissues. MFS were associated (in samples from inoculated trees) with cleavage and desquamation of fungal walls. ES and MFS did not label for cellulose or chitin, but generally labelled slightly for β-(1-3)-glucan and mannose, and strongly for galactose. Only the lucent, inner fungal wall layer labelled for chitin and cellulose. DNA labelling was confined to nuclei and mitochondria in fungal cells from cultures on agar medium; in cells from cultures on millipore membranes, it was pronounced over imprecisely delimited cell regions. The possible ontogeny of MFS components and their importance are discussed. Résumé: Des observations ultrastructurales montrent la présence de structures d'allure micro-filamenteuses (MFS) et tubulaires dans les parois et gaines extracellulaires (ES) des cellules de l'Ophiostoma novo-ulmi Brasier poussant sur divers milieux et dans son hôte et soumis à divers traitements. Fixés chimiquement ou cryogéniquement (par haute pression d'azote liquide), certains des échantillons ont été traités avec des sondes marquées pour détecter des composés pariétaux du champignon et de l'hôte, et dans quelques cas l'ADN. Les examens ont porté également sur des coupes sériées de 0,2 µm, à 120 kV et inclinées au goniomètre afin d'obtenir une vue stéréoscopique des structures. La présence de MFS a été perçue dans les cellules fongiques, munies de parois typiques (avec une couche extérieure opaque et une autre intérieure translucide) comme dans les cellules ayant une seule couche pariétale, opaque et mince.Ces MFS pouvaient s'étendre du cytoplasme de la cellule fongique à travers ses parois jusque dans le milieu environnant, y inclus les structures des cellules hôtes dans le cas de tissus d'orme infectés. Dans les échantillons d'arbres inoculés, on a observé des clivages et exfoliations des parois des cellules fongiques, conjointement avec les MFS qui s'y trouvaient liées. Le β-(1-3)-glucane et le mannose ont été décelés en petite quantité dans la couche ES et dans les MFS, le galactose l'a été en plus grande quantité, alors que la chitine et la cellulose n'ont été détectées que dans les parois internes des cellules fongiques. Le marquage pour l'ADN était bien distin...

Histopathology of Fusarium wilt of staghorn sumac (Rhus typhina) caused by Fusarium oxysporum f. sp. callistephi race 3. II. Characteristics of opaque matter associated with extensive host cell and cell wall alterations

“…The present observations reinforce the hypothesis, as already expressed for other systems and supported by similar observations (Ouellette and Baayen 2000;Ouellette and Rioux 1993;Ouellette et al 1995Ouellette et al , 1999aOuellette et al , 2004aOuellette et al , 2004bOuellette et al , 2004cOuellette et al , 2004d, that the OM occurrence primarily relates to the pathogen, as: 1) OM, including that of the VWLM, was also connected to fungal cells, and often by means of microfilaments (see also Atstatt 2003, showing some endophyte-like fungal cells with their walls pervaded by similar filamenatous structures); and 2) close similarities noted between OM present in host walls or in periplasmic areas, that of the VWLM, and content of some fungal cells and elements (compare Figs. 6d,7d,8c and element in Fig.…”

“…These ranged from peculiar breakdown of pit membranes of bordered pits, degradation of parenchyma cell walls, pervasion and alterations of vessel secondary walls by matter extending from their lining material and so on. These observations paralleled some of those made regarding other wilt diseases, in particular of elms infected by Ophiostoma novo-ulmi Brasier (Ouellette 1978;Ouellette andRioux 1992, 1993;Ouellette et al 1995Ouellette et al , 1999aOuellette et al , 2004a and of eggplant infected by Verticillium dahliae Kleb. (unpublished observations).…”

Extracellular sheath formation by Sphaeropsis hypodermia and association with its infection in elm trees

“…In addition to the examples referred to in Ouellette et al (1999b) we may cite : Carver et al 1999;Frederick et al 1999;Hoffert et al 1995. The extracellular components in S. hypodermia may be related to those présent intercellularly in the sclerotia formed by some fungi (Kohn and Grenville 1989;McLaren et al 1989;Willetts et al 1990).…”

“…The production of abundant extracellular material in several fungai pathogens is suspected to be of great importance in pathogenesis in a number of plant diseases, including Dutch elm disease (Ouellette et al 1999b; see citations concerning some of the other cases). Isolating and producing probes for the possible components of the extracellular sheath that forms under various conditions in S. hypodermia would undoubtedly contribute to a better understanding of the rôle of such components in host tissue invasion in this case as in other plant diseases.…”

Distributed Physical and Molecular Separations for Selective Harvest of Higher Value Wheat Straw Components Project

“…A hyphal sheath, consisting of a thin glucan layer, was previously observed for a closely related fungal species, P. eryngii ). Hyphal sheaths have been observed around many wood decay fungi (Palmer et al 1983aand b, Highley et al 1983, Ruel and Joseleau 1991, Green et al 1992, Jellison et al 1997) and sapstaining fungi (Schmid and Liese 1965, Gharibian et al 1996, Ouellette et al 1999, Schirp 2001 Final Report extracellular enzymes from inactivation and retain them close to the fungal hyphae. Optimal pH levels of 7 to 9 have been reported for xylanases and pectinases, therefore, the extracellular sheath may also serve to maintain an environment favorable to enzyme activity since wood is acidic, with a typical pH of 4-5 (Gharibian et al 1996).…”