Mycelium

Abstract: We describe a general, simple and inexpensive method for the isolation of DNA from filamentous fungi. Starting from freeze-dried mycelium 01–015% by weight can be isolated as high molecular weight DNA suitable for restriction and ligation in 2 h. The preparation can be done in Eppendorf tubes and allows the processing of many samples in parallel. We have used the method with the basidiomycetes Phanerochaete chrysosporium, Coprinus cinereus and the ascomycete Aspergillus nidulans and others have used it with Trichoderma reesei, Aspergillus niger and for the isolation of DNA from tomato plants.

Abstract: Summary The enzyme nitrate reductase (NADPH: nitrate oxidoreductase, EC 1.6.6.3) is present only in mycelium grown in the presence of nitrate and absence of ammonium. Techniques have been devised for studying the kinetics of nitrate reductase appearance in mycelium upon the addition of nitrate to the medium. Changes in the level of nitrate reductase in mycelium transferred from nitrate to nitrate, ammonium, and glutamate, used singly or in combination as nitrogen sources have also been studied. The result of such experiments indicate that the synthesis of nitrate reductase is induced by nitrate and repressed by ammonium. No effect in vitro of ammonium could be found. Upon induction at 25° there was a lag of about 8 min before enzyme began to appear. The rate of production per unit volume of medium thereafter decreased for about 1 h, and then became constant, even though mycelial mass per unit volume of medium increased throughout the experiment. At no time therefore, in contrast to most Escherichia coli systems, was rate of induction directly proportional to mycelial mass.

Abstract: The discovery of a previously unknown mechanism of nitrogen transfer from the arbuscular mycorrhizal fungi found on the roots of most land plants, to the host plants suggests that this symbiotic relationship may be a much more important factor in the global nitrogen cycle than was thought. The mechanism involves uptake of inorganic nitrogen by the fungus outside the roots, conversion to amino acids within the fungus, then transfer as ammonium ions from the fungal mycelium into the plant. The first event in host recognition by arbuscular mycorrhizal fungi is thought to be hyphal branching. A strigolactone, 5-deoxy-strigol, isolated from Lotus japonicus has now been identified as an inducer of branching. Strigolactones are root metabolites, previously isolated as seed germination stimulants for root parasitic weeds. This finding highlights the close relationship between plant and fungus, and may provide a new strategy for the control of both beneficial fungal symbionts and destructive parasitic weeds in agriculture and natural ecosystems. Most land plants are symbiotic with arbuscular mycorrhizal fungi (AMF), which take up mineral nutrients from the soil and exchange them with plants for photosynthetically fixed carbon. This exchange is a significant factor in global nutrient cycles1 as well as in the ecology2, evolution3 and physiology4 of plants. Despite its importance as a nutrient, very little is known about how AMF take up nitrogen and transfer it to their host plants5. Here we report the results of stable isotope labelling experiments showing that inorganic nitrogen taken up by the fungus outside the roots is incorporated into amino acids, translocated from the extraradical to the intraradical mycelium as arginine, but transferred to the plant without carbon. Consistent with this mechanism, the genes of primary nitrogen assimilation are preferentially expressed in the extraradical tissues, whereas genes associated with arginine breakdown are more highly expressed in the intraradical mycelium. Strong changes in the expression of these genes in response to nitrogen availability and form also support the operation of this novel metabolic pathway in the arbuscular mycorrhizal symbiosis.

Abstract: Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen causing disease in a wide range of plants. This review summarizes current knowledge of mechanisms employed by the fungus to parasitize its host with emphasis on biology, physiology and molecular aspects of pathogenicity. In addition, current tools for research and strategies to combat S. sclerotiorum are discussed. Taxonomy: Sclerotinia sclerotiorum (Lib.) de Bary: kingdom Fungi, phylum Ascomycota, class Discomycetes, order Helotiales, family Sclerotiniaceae, genus Sclerotinia. Identification: Hyphae are hyaline, septate, branched and multinucleate. Mycelium may appear white to tan in culture and in planta. No asexual conidia are produced. Long-term survival is mediated through the sclerotium; a pigmented, multi-hyphal structure that can remain viable over long periods of time under unfavourable conditions for growth. Sclerotia can germinate to produce mycelia or apothecia depending on environmental conditions. Apothecia produce ascospores, which are the primary means of infection in most host plants. Host range: S. sclerotiorum is capable of colonizing over 400 plant species found worldwide. The majority of these species are dicotyledonous, although a number of agriculturally significant monocotyledonous plants are also hosts. Disease symptoms: Leaves usually have water-soaked lesions that expand rapidly and move down the petiole into the stem. Infected stems of some species will first develop dark lesions whereas the initial indication in other hosts is the appearance of water-soaked stem lesions. Lesions usually develop into necrotic tissues that subsequently develop patches of fluffy white mycelium, often with sclerotia, which is the most obvious sign of plants infected with S. sclerotiorum.

Abstract: Mycorrhizal fungi form extensive mycelia in soil and play significant roles in most soil ecosystems. The estimation of their biomasses is thus of importance in order to understand their possible role in soil nutrient processes. For arbuscular mycorrhizal (AM) fungi the signature fatty acid 16:1ω5 provides a new and promising tool for the estimation of AM fungal biomass in soil and roots. For ectomycorrhizal fungi 18:2ω6,9 dominates among the fatty acids and can be used as an indicator of mycelial biomass of these fungi in soil in experimental systems. In biomass estimation primarily the phospholipid fatty acids (PLFAs) are suitable. Through the use of specific PLFAs it is possible to study interactions between mycorrhizal mycelia and bacteria in soil as well as between AM fungal mycelia and mycelia of saprophytic and parasitic fungi in soil and in roots. AM fungi, in particular, store a large proportion of their energy as lipids and by using the signature fatty acids it is possible to determine the relation between membrane and storage lipids, which could be an indication of energy storage levels. Various aspects of how the fatty acid signatures can be used for studies related to questions of biomass distribution and nutritional status of mycorrhizal fungi are discussed.