Jean Dexheimer

Mycorrhizal status of some fungi fruiting beneath indigenous trees in Burkina Faso

Abstract During the rainy season, putative ectomycorrhizal fungi were observed under three species of Caesalpinioideae Afzelia africana Sm., Isoberlinia doka Craib. and Stapf. and Isoberlinia dalziellii Craib. and Stapf., one species of Dipterocarpaceae Monotes kerstingii Gilg. and two species of Euphorbiaceae Uapaca guineensis Mull. Arg. and Uapaca somon Aub. and Lean. The fungi belong to the orders of Agaricales, Aphyllophorales, Boletales, Cantharellales, Gautieriales, Hymenogastrales, Russulales and Sclerodermatales. Some of these fungal species e.g. Lactarius gymnocarpus Heim., Cantharellus pseudofriesii Heinem., Scleroderma dictyosporum Pat., Scleroderma verrucosum Pers., Scleroderma sp2 and Russula sp1, are common to the tropical tree families known to form ectomycorrhizas. A few species of these fungi e.g. Amanita hemibapha (Berk. and Br.) Sacc., Inocybe sp1, Boletellus sp3, Lactarius sp2 and Xerocomus subspinulosus Heinem., are observed only under mycorrhizal trees belonging to the group of Caesalpinioideae legumes. However, seven fungal species Coltricia cinnamomea (Pers.) Murr., Boletellus sp5, Austrogautiera sp. (hypogeous), Lactarius sp1, Russula annulata Heim., Russula sp2 and Scleroderma sp1 seem more specific to the Uapaca species. In all, twenty-seven putative ectomycorrhizal fungi were recovered and only five fungal species were isolated from sporocarps and maintained in pure culture. Four Scleroderma species were confirmed as mycorrhizal fungi on A. africana, Isoberlinia spp. and two East African trees, Brachystegia speciformis Benth. and Afzelia quanzensis Welw. The two Uapaca species, B. speciformis and M. kerstingii possess both arbuscular mycorrhizas and ectomycorrhizas.

Ultrastructural Cytochemistry of the Host-Fungus Interfaces in the Endornycorrhizal Association Glomus mosseae / Allium cepa

Summary The structure of the host-fungus interface in the VA mycorrhizal association Glomus mosseae / Allium cepa has been investigated cytochemically (Thiery test; differential DMSO and EDTA extraction; phosphotungstic acid staining) and using different fixation procedures (glutaraldehyde and OsO 4 post-fixation; simultaneous glutaraldehyde — OSO 4 fixation). The continous, highly invaginated host plasmalemma surrounding the intracellular fungal structures retains its affinity for phosphotungstic acid and continues to produce polysaccharide fibrils, but in the presence of the endophyte it progressively loses the capacity to organise these into well-structured wall material. At the point of cell penetration and in the primary arbuscule branches the fungal wall, which is stained by the Thiery reaction and phosphotungstic acid but unaffected by DMSO or EDTA, is surrounded by a collar of host wall material which has the same cytochemical properties as the primary walls of the plant cell. The fine arbuscule branches are surrounded by a layer of condensed matrical fibrils. When the arbuscule branches senesce and collapse, they become encased by the polysaccharide fibrillar material derived from the host. The appearance of the interfacial matrix separating the host plasmalemma from the fungal wall is always the same, no matter which fixation procedure is used. It contains membranous vesicles and scattered polysaccharide fibrils, both of which are elaborated by the host plasmalemma. The importance of the host and endophyte plasmalemma formations is emphasised. The vesicles arising from the host plasmalemma are often in contact with the walls of the endophytic hyphae. In the fungus, these bulbous or tubular configurations of the plasmalemma can become very numerous and can occupy the whole hyphal width. Although these structures could be involved in host-fungus exchanges, their eventual participation in wall synthesis is also orooosed.

Role of the host-arbuscule interface in the VA mycorrhizal symbiosis: ultracytological studies of processes involved in phosphate and carbohydrate exchange

Summary The host-arbuscule interface does not vary greatly between different VAM associations of herbaceous and woody plants. The presence in the interfacial matrix of living fine arbuscule branches, where the host wall material is reduced or nonexistent and the endophyte wall is thin, of host membranous vesicles, polysaccharides, ATPase and neutral phosphatase activities, clearly indicates that this structure is not an inert space, but a physiologically complex zone. Possible roles for these interfacial matrix components in host-fungus nutrient exchange is discussed.

Plasmalemma Structure and Function in Endomycorrhizal Symbioses

Summary Ultracytological and ultracytoenzymological studies indicate that there are no adverse alterations in either fungal or plant plasmalemma during intracellur host-fungus interactions in symbiotic ericoid and vesicular-arbuscular endomycorrhizas. These observations are discussed in relation to those reported for biotrophic pathogen infections in plants.

Etude de la Sécrétion de Mucilage par les Cellules des Glandes Digestives de Drosera capensis L.: Localisation Ultrastructurale des Phosphatases Neutres et de l'ATPase

Summary This paper describes a study of the localization of phosphatase activity, detected at a pH close to neutral, in the digestive cells of Drosera capensis during the mucilage-forming phase. The author distinguishes between an ATPase activity and a neutral phosphatase activity detected using IDP, TPP and sodium β-glycerophosphate as substrates. During the initial mucilage-forming phase, the neutral phosphatase activity in the cytoplasm is present in the dictyosomes, along the membranes of the enormous secretory vesicles and on the plasmalemma. The activity is very diffuse in the cell walls. In the course of the following phases, the phosphatase activity disappears from the dictyosomes but remains on the plasmalemma. The cell walls become very active, but the activity is limited to the zone where mucilage accumulates. Cytoplasmic ATPase activity is limited to the plasmalemma. In the cell walls, the activity is concentrated, as is that of the other phosphatases, in the median zone. Finally, the very intense reactivity of the cuticular pores shows that all these enzymes are exuded from the gland. The presence of neutral phosphatases activity in the dictyosomes, during mucilage synthesis, indicates structural and functional differentiation of these organelles. The presence of intense activity along the plasmalemma may be explained in terms of active transport phenomena. However, the role of phosphatase activity in the mucilage excreted outside the gland remains to be explained.

Application de quelques techniques cytochimiques à l'étude des interfaces des ectendomycorhizes de Monotrope (Monotropa hypopitys L.)

Summary The interfacial organization of ectendomycorrhizas of monotropa was studied with different cytochemical methods. The ectomycorrhizal part comprises a thick sheath and a reduced Hartig net. The extractions by DMSO or EDTA show that the cement has an heterogenous structure. The middle part, between the hyphae, contains a fibrillar poly—saccharidic material which is insensitive to chemical extractions. This material is associated with proteins. The chitin, which is characteristic of fungal wall, is not present in the cement. The endomycorrhizal part is reduced to non—branched intracellular hyphae which are in continuity with those of the mantle. As in the other kinds of endomycorrhizas, the host cell intracellular hyphae and the partners are always separated by a mixed apoplasm. The fungal wall is covered with a complex apposition layer. The zone in contact with the fungal wall is similar to the cement of the ectomycorrhiza. The apposition layer bears polysaccharidic finger—like protuberances which a...

Etude de l'origine et de la répartition des granules vacuolaires dans les hyphes d'une endomycorhize à vésicules et arbuscules

Summary The authors have observed three different types of inclusions in hyphae of the endophyte: dense vacuolar granules, less dense and often diffuse vacuolar granules and granules included in small cytoplasmic vesicles. These inclusions were studied by cytochemical techniques and by energy electron loss spectroscopy. Dense granules correspond to polyphosphate granules already described by many authors. They contain phosphorus and calcium associated with a proteic fraction. Cytoplasmic granules and diffuse vacuolar granules are protein-rich inclusions without phosphorus and calcium. The authors suggest that the cytoplasmic inclusions are precursors of polyphosphate granules. These inclusions are contained in unknown origin vesicles. The diffuse protein-rich vacuolar granules are the remaining of polyphosphate granules after the transfer of phosphorus to the host. The polyphosphate granules are common in intracellular hyphae, but more rare and often absent in the hyphae of the arbuscule. For the authors,...

Etude du statut mycorhizien de quelques plantes de serre

Summary Authors have researched VA mycorrhizal symbiosis in root system of xerophytous plants in the Botanical Garden of Nancy. They have examined 9 families and 22 species. For most of species, they have observed well developed VA endomycorrhizae. Nevertheless, these mycorrhizae have not been observed in roots of Cactaceae and Aizoaceae. The presence of mycorrhizae, even in plants that have been treated, incites to integrate mycorrhizal symbiosis in techniques of cultivation of greenhouse plants.

Le traitement d'images en biologie ou la chambre noire digitale

Summary Techniques of image processing are now accessible with personal computers. The initial phase of the processing is the digitalization of images. It can be achieved by the capture of a video signal, with a scanner or with a photographic CD. Digital images can undergo various processings (modifications of the pixels, filters, false color, superposition of images) whose purpose is to improve the quality of the documents or to show some details. It is fundamental for scientific documents to avoid the modification or the loss of the information during the processing. Techniques of image processing are going to know many applications in the exploitation of biological photographic documents.

Etude des modalités de la mycorhization de pivots d'Eucalyptus globulus développés en clinostat

Summary The present study analyze the aptitude to the mycorrhization with Pisolithus tinctorius of tap root of seedlings of Eucalyptus globulus grown in a clinostat. Unlike the vertical tap roots developed in normal conditions, these tap roots are strongly colonized. The fungus builds an ectomycorrhiza with a dense mantle and massive intercellular structures equivalent to an Hartig net. Physiological perturbations, induced by the modification of the growth of the tap root, would be involved in the mycorrhization.