Étude morphologique, anatomique et ultrastructurale d'endomycorhizes synthétiques d'Erica carnea

Abstract

Endomycorrhizae were synthesized between Erica carnea and a fungus isolated from E. vagans. Inoculated and non-inoculated plants were grown for 6 months under controlled conditions. Inoculation provokes an important stimulation of the growth and flowering of E. carnea. Under the experimental conditions reported herein, the mycorrhizae formed during the 1st month remained localised and, after 6 months, the roots usually were not colonized by the fungus. It seems probable that colonization of the whole root system requires a growth substrate that favours mycelial growth.Macroscopic and microscopic characters of the mycorrhizae obtained were studied using light and scanning (SEM) and transmission (TEM) electron microscopy. The hyphae of the responsible fungus exhibit simple septa and Woronin bodies (ascomycetes). The intracellular hyphae are characterised by the abundance of lipid globules and the presence in SEM of electron-dense granules in the vacuoles. These hyphae are wrapped in a network of fibrils particularly at the penetration points but also observed on external hyphae. These mycorrhizae seem to survive for approximately 1 month only. The importance of the inoculum as nutritional source must not be neglected since similar stimulation of the plants was also produced by inoculation with an autoclaved slurry of mycelium. We suggest that not only mycorrhizal but also saprophytic rhizosphere fungi free, by simple autolysis of their mycelia, elements that are assimilable by the plant and doubtless play a role in the mineral nutrition of the Ericaceae.

Biology of mycorrhizal associations of epacrids (Ericaceae)

“…It is not known whether colonisation increases the total number of roots or promotes growth of hair roots in epacrids, as has been shown by Berta et al . (1988) for C. vulgaris and by Duclos et al . (1983) for Erica carnea L. It is therefore not clear how widespread this phenomenon is or how many endophytes promote the response.…”

Ultrastructural Aspects of Endomycorrhiza in the Ericaceae

“…When the fungus is associated with non-host plants, the behaviour of the two organisms contrasts sharply with that observed in mycorrhizal associations. The biotrophic stages of host-fungus interactions in ericoid mycorrhizas, which have now been described in a wide range of naturally and axenically infected host plants (Bonfante-Fasolo & Gianinazzi- Pearson, 1979Pearson, , 1982Peterson, Mueller & Englander, 1980;StruUu & Gourret, 1980;Bonfante-Fasolo et aL, 1981;Duddridge & Read, 1982;Duclos, Pepin & Bruchet, 1983), and which are illustrated in the present work, are characterized at the cellular level by a dramatic increase in the volume of host cytoplasm and proliferation of host organelles. These are both characteristics of metabolically active cells and are normally observed in juvenile plant cells.…”

Mycorrhizas: Integrated Development between Roots and Fungi

“…ing hypha, is initiated (Bonfante-Fasolo and Gianinazzi-Pearson, 1982) and from this a thin septate hypha penetrates the epidermal cell wall (see also Duclos et al, 1983). Changes in the epidermal cell wall are con?…”

“…All of the ericoid species studied have a common type of intracellular colonization. Coils of hyphae occupy most ofthe volume of epidermal cells(Bonfante- Fasolo and Gianinazzi-Pearson, 1982;Duclos et al, 1983); apparently hyphae do not pass between adjacent epidermal cells (Bonfante-Fasolo and Gianinazzi-Pear?…”