Báo cáo lâm nghiệp: "Experimental study of pine ectomycorrhizae: ectomycorrhizal organization after girdling of the hypocoty"

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Experimental study of pine ectomycorrhizae: ectomycorrhizal organization after girdling of the hypocotyl J. Lei J. Dexheimer J.E. CNFiS 034613, Universite de BP 239. 54506 Laboratoire de Biologie des Nancy I, Ligneux, Vandceuvre Cedex, France In about 10 days, the thickness of the Numerous authors have already described mantle is reduced and its structure the ultrastructural organization of ectotro- phic mycorrhizas in various species. In the becomes increasingly loose. Twenty days after girdling, the mantle is replaced by a present work, we studied how the ectomy- loose network which is very different from corrhizal architecture is modified when the the usual mycelial sleeve (Fig. 5). host plant-fungus equilibrium is disturbed, by girdling the hypocotyl of Pinus sylves- Hartig net also has an abnormal The tris plantlets mycorrhized by Hebeloma (Figs. 6 and 7). Like the mantle, structure crustuliniforme or Paxillus involutus. This it becomes less dense and, in most cases, stops the flow of sugars to the roots. the hyphae are bordered by dead cortical We examined the changes in mycorrhi- cells which are often filled with tannins. zal structure and function at different time Moreover, the component hyphae have an intervals. unusual behavior as they give off branch- Girdling of the host plant causes exten- es which penetrate into the host cells. sive changes in both partners leading Sometimes these branches penetrate morphologically in the pine to the swelling dead cells and the only change is a perf- of the stem above the ablation (Fig. 1 ) and oration of the wall. In other cases, the in the fungal partner to the more or less branches penetrate into a living cell as complete disappearance of the intramatri- shown by the existence of a parietal papil- cal mycelium (Figs. 2 and 3). la at the penetration site (Fig. 8). Such papillae are well known in biotrophic para- The swelling of the stem is characteris- sitic infections (Berlin and Bowen, 1964; tic of plants that have undergone girdling. Heath and Heath, 1971; Littlefield and The products of photosynthesis in the Bracker, 1972; Hohl and Stossel, 1976; aerial part are blocked by girdling and can Higgins and Lazarovits, 1978; Beakes et no longer migrate into the root system al., 1982) and are considered to be the (Zimmermann, 1969). result of a host defense mechanism. This operation also induces a profound transformation of mycorrhizal structure The girdling of the host plant not only (Figs. 4 and 5). induces morphological changes but also
affects mycorrhizal function, as demon- References strated by experiments showing the locali- zation of ATPase activities. In a ’normal’ Beakes G.W., Singh H. & Dickinson C.H. (1982) mycorrhiza, the ATPase activities are Ultrastructure of the host-pathogen interface of Peronospora viciae in cultivars of pea which observed on the fungal plasmalemma in show different susceptibilities. Plant Pathol. 31, the mantle and on the plasmalemma of 343-354 the fungus and host cortical cells in the Berlin D. & Bowen C.C. (1964) The host-para- Hartig net (Lei and Dexheimer, 1988). site interface of .Albugo candida on Raphanus sativus. Am. J. Bot. 51, 445-452 In mycorrhiza of host plants that have Heath M.C. & Heath LB. (1971 ) Ultrastructure undergone girdling, there is no ATPase of an immune and a susceptible reaction of activity in the Hartig net (Figs. 9 and 10). cowpea leaves to rust infection. Physiol. Plant This suggests a change in the relationship Pathol. 1, 277-287 between the partners. These metabolic Higgins V.J. & Lazearovits G.L. (1978) Histo- changes were already present before any pathological and ultrastructural comparison of Stemphylium sarcinaeforme and S. botryosum morphological transformation. on red clover foliage. Can. J. Bot. 56, 2097- Finally, the penetration of the Hartig net 2108 hyphae inside living cells and papilla for- Hohl H.R. & Stossel P. (1976) Host-parasite interfaces in a resistant and a susceptible culti- mation suggest that, under these condi- var of Solanum tuberosum inoculated with tions, the fungal partner presents a parasi- Phytophthora inf, tuber tissue. Can. J. stans: 9 tic type of behavior and damages cortical Bot. 54, 900-912 2 cells to obtain the metabolites that it Lei J. & Dexheimer J. (1988) Study of the requires. This interpretation is also con- basidiomycete ectomycorrhizas. Ultrastructural firmed by the more or less complete lysis localization of ATPase activity in the Pinus syl- vestrislLaccaria laccata association. New Phy- of walls of cortical cells in contact with the tol. 108, 329-337 hyphae of the Hartig net. Littlefield L.J. & Bracker C.E. (1972) Ultrastruc- tural specialization at the host-pathogen inter- Hence, the aisturbance of the symbiotic face in rust-infected flax. Protoplasma 74, 271- equilibrium induced by girdling of the host 305 plant leads to a change in the structure of Zimmermann M. (1969) Translocation of nutri- the mycorrhiza and a change in the rela- ents. In: The Physiology of Plant Growth and tionship between the two partners from Development. (M.B. Wilkins, ed.), McGraw-Hill, symbiosis to parasitism. London, pp. 383-417 7