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  • 1
    ISSN: 1432-2048
    Keywords: Ectomycorrhiza ; Elicitor inactivation ; Elicitor-induced reaction ; Hebeloma — Picea cells ; Signal transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Elicitors released from hyphae or cell walls of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) Quél. induced in suspension-cultured cells of Picea abies (L.) Karst. a set of fast reactions: (i) an immediate efflux of Cl− into the medium, followed by a K+ efflux; (ii) an influx of Ca2+ (measured as accumulation of 45Ca2+ in the cells); (iii) a phosphorylation of a 63-kDa protein and dephosphorylation of a 65-kDa protein (detectable by 4 min after elicitor application); (iv) an alkalinization of the medium, and (v) a transient synthesis of H2O2. The removal of extracellular Ca2+ by EGTA delayed the elicitor-induced alkalinization. A further reduction of this response could be achieved by TMB-8 an inhibitor of Ca2+ release from intracellular stores. Moreover, the inhibition of protein kinase activity by staurosporine prevented the extracellular alkalinization completely. However, the effectiveness of the elicitors in inducing the extracellular alkalinization was strongly impaired by constitutively secreted enzymes of spruce cells which cleaved the elicitors to inactive fragments. It is suggested that in ectomycorrhizae the efficacy of elicitors released from fungal cell walls is controlled by apoplastic enzymes of the host; the plant itself is able to reduce the activity of fungal elicitors on their way through the plant cell wall. But those elicitors which finally reach the plasma membrane of host cells induce reactions that are similar to the early defense reactions in plant-pathogen interactions.
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  • 2
    ISSN: 1432-2048
    Keywords: Key words: Chitinase ; Chitin elicitor ; Ectomycorrhiza ; Hebeloma ; Picea ; Plant defence (suppression)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Rapid reactions comprising efflux of K+ and Cl−, phosphorylation of a 63-kDa protein (pp63), extracellular alkalinization and synthesis of H2O2 are equally induced in cells of Picea abies (L.) Karst. by chitotetraose, colloidal chitin and cell wall elicitors from the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) Quél. an ectomycorrhizal partner of spruce. Cleavage of fungal cell wall elicitors and of artificial chitin elicitors to monomeric and dimeric fragments by apoplasmic spruce chitinases (36-kDa class I chitinase, pI 8.0, and 28-kDa chitinase, pI 8.7; EC 3.2.1.14) equally prevented induction of these rapid reactions. Also, N-acetylglucosamine oligomers and elicitors from the fungal cell walls showed a similar dependence of their activity on the degree of polymerisation. From these results it is suggested that, during ectomycorrhiza formation, only some of the chitin-derived elicitors reach their receptors at the plant plasma membrane, initiating reactions of the hypersensitive response in the host cells. The remaining fungal elicitors will be degraded to varying extents by wall-localized chitinases of the host root, reducing the defence reactions of the plant and allowing symbiotic interactions of both organisms.
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  • 3
    ISSN: 1432-2048
    Keywords: Key words: Cantharidin ; Ectomycorrhiza ; Elicitor-induced reactions ; Mastoparan ; Picea ; Protein Phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The first responses in spruce [Picea abies (L.) Karst.] cells induced by elicitors (N-acetylglucosamine oligomers) from ectomycorrhizal fungi have been described as follows: efflux of Cl− and K+, influx of Ca2+, extracellular alkalinization, phosphorylation of a 63-kDa protein (pp63), dephosphorylation of a 65-kDa protein (pp65) and synthesis of H2O2 (Salzer et al. 1996, Planta 198: 118–126). In order to obtain new insights into the triggering mechanism and the sequence of these rapid responses we used compounds which are known to activate or block specific steps within an elicitor-induced signal transduction cascade in plant cells. Comparable to elicitors the two protein phosphatase inhibitors, cantharidin and calyculin A, as well as mastoparan, an activator of trimeric G-proteins, were able to induce the release of Cl− and K+ from spruce cells and the alkalinization of the medium. Half-maximal activation of the alkalinization occurred at 133 nM calyculin A, 2.3 μM cantharidin and 1.6 μ mastoparan. The structural analogue of mastoparan, Mas 17, which has no G-protein-stimulating properties, was unable to trigger the above-mentioned reactions. In addition, cantharidin and calyculin A induced an increased synthesis of H2O2 in spruce cells which was prolonged in comparison to the elicitor-induced transient formation of H2O2. Also, the cantharidin-induced release of K+ was more pronounced and longer lasting than that caused by elicitors from the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) and N-acetylglucosamine oligomers. Furthermore, cantharidin, calyculin A and mastoparan induced the phosphorylation of pp63. Remarkably, the protein kinase inhibitor, staurosporine, inhibited all the rapid responses described above, no matter whether they were triggered by fungal elicitors or by the protein phosphatase inhibitors. These results indicate that in the initial signalling events in spruce cells, essential protein phosphorylations occur either as an (auto) phosphorylation of a membrane-bound receptor kinase prior to the activation of a G-protein or (and) immediately downstream of the activated G-protein in a phosphorylation cascade and are the basic requirements for the ion fluxes following downstream.
    Type of Medium: Electronic Resource
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