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Research examines the dynamics and determinants of carbon isotopic fractionation in basidiomycete fungi in relation to their growth cycle. Results indicate that isotope fractionation does vary depending on the ecophysiological conditions of the media in which fungi are growing. Results establish conditions which influence natural stable carbon isotope distributions.

Isotopic fractionation in three species of basidiomycete species using different sources of sugar in their ecosystem environment is presented. Results show that the fungi differentially fractionate sucrose derived from C(sub)3 and C(sub)4 in a taxon-specific manner and that the fractionation is sensitive to the nonrandom distribution of the stable isotope.

Author(s): David Quist; Ignacio H. Chapela (corresponding author) Quist and Chapela reply Our original publication [1] contained two separate conclusions derived from two methodological approaches. First, using PCR, we detected [...]

Author(s): Ignacio H. Chapela [1] Sir James, Gaston and Balmford in their Commentary provide confused arguments for a global conservation strategy [1]. The fault lies in their jump from an [...]

To quantify and characterize N and C isotopic fractionation effects due to fungal transformation of organic substrates in forest ecosystems, we performed a field study in California and a meta-analysis of three additional studies conducted by others across the Northern Hemisphere. Basidiomycete fungal biomass was consistently enriched for the heavier isotope for C relative to substrate and either enriched or depleted for N relative to atmospheric N. Extent and pattern of fractionation was very variable, but the distinction between ectomycorrhizal and saprotrophic basidiomycetes was strongly supported, particularly when dual isotope analyses were performed. This differentiation, which we call the "EM-SAP Divide" holds for studies within a restricted ecosystem, but becomes less distinct over larger geographical regions, removing the rationale for using direct isotopic values from single specimens as diagnostic of ecophysiological role. For C, the EM-SAP Divide seems to reflect substrate effects, potentially due to differential access to recently synthesized versus recycled organic compounds, rather than distinct physiological pathways. Once substrate and ecophysiological role effects are removed, our meta-analysis suggests the existence of more than one mechanism causing C fractionations in fungi which is found equally in ectomycorrhizal and saprotrophic fungi. Similarly, a multimodal distribution of δ15N values suggests that physiological effects may play a much stronger influence on N natural isotopic distributions in fungi. Our meta-analysis provides a firm statistical base to evaluate fungal ecological statements based on natural isotopic distributions of C and N. We call into question the current practice of using direct isotopic measurements to make statements about trophic relationships of fungi in the absence of other supporting evidence. [ABSTRACT FROM AUTHOR]

The role of the conidial sheath in the recognition process and in the attachment of conidia of the beech endophyte, Discula umbrinella, to the host surface was investigated . After treatment of conidia with different lectins the adhesion of conidia to the host surface was effectively inhibited. A strong fluorescence was observed after treatment of conidia with TRITC-labelled concanavalin A. Fluorescence with TRITC-labelled wheat germ agglutinin was observed only on spores subjected to enzymatic digestion with proteases. Observations with the transmission electron microscope (TEM), after labelling sections with colloidal gold conjugated lectins, confirmed the presence of mannose and/or glucose in the extracellular sheath. Chitin was present in the conidial cell wall but not in the extracellular sheath. Enzymatic treatment of the conidial sheath resulted in strongly reduced attachment and changes in the binding of fluorescence-labelled lectins. TEM studies of partially digested conidia revealed that snail enzyme modified only slightly the structure of the sheath, while proteases completely dissolved the fibrillar sheath leaving a comparatively smooth cell wall with no fibrillar structures on its surface. We conclude that a proteinaceous sheath is responsible for the adhesion of Discula umbrinella conidia to the host and that glycoproteins are involved in the recognition and attachment process. This attachment mechanism closely parallels the only other recognition system studied biochemically in endophytes, and is similar to the few analogous cases studied in plant-pathogenic fungi, pointing to the functional relatedness of endophytic and pathogenic interactions. [ABSTRACT FROM AUTHOR]

Investigates the dynamics and determinants of C isotopic fractionation for 11 basidiomycetes that represent ectomycorrhizal (EM) and saprotrophic (SAP) fungi under controlled substrate conditions. Growth of 11 basidiomycetes in axenic culture; Relationship between the observed isotope fractionation and the growth stage of their mycelium.