Showing papers on "Mycelium published in 1996"

Plant Cell Responses to Arbuscular Mycorrhizal Fungi: Getting to the Roots of the Symbiosis.

Abstract: Since their colonization of terrestrial ecosystems, plants have developed numerous strategies to cope with the diverse bi? otic and abiotic challenges that are a consequence of their sedentary life cycle. One of the most successful strategies is the ability of root systems to establish mutualistic and reciprocally beneficial symbiotic relationships with microorganisms. Mycorrhizas, the intricate associations roots form with specific fungal groups, are by far the most frequent of these and rep? resent the underground absorbing organs of most plants in nature (Gianinazzi-Pearson, 1984). Through their function in the efficient exploitation of soil mineral resources and their bioprotective role against a number of common soilborne pathogens, mycorrhizas are instrumental in the survival and fitness of many plant taxa in diverse ecosystems, including many crop species (reviewed in Allen, 1991; Bethlenfalvay and Linderman, 1992). Several kinds of mycorrhizal associations can be distin? guished according to their morphology and the plant and fungal taxa concerned. They fail almost exclusively into two broad groups: (1) the ectomycorrhizas of woody Angiosperms and Gymnosperms, in which Basidiomycetes, Ascomycetes, or Zygomycetes develop intercellular hyphae from a mycelial sheath covering the surface of short lateral roots; and (2) the endomycorrhizas, characterized by intraradical mycelium growth and intracellular fungal proliferation, which are formed by Basidiomycetes in the Orchidaceae (orchidoid mycorrhiza), Ascomycetes in the Ericales (ericoid mycorrhiza), and Zygomy? cetes in most other terrestrial plant taxa (arbuscular mycorrhiza; reviewed in Harley and Smith, 1983). Plant compatibility with mycorrhizal fungi is a generalized and ancient phenomenon. Species in >80?/o of extant plant families are capable of establishing arbuscular mycorrhiza (AM), and fossil evidence suggests that symbioses of this kind existed >400 million years ago in the tissues of the first land plants (Pirozynski and Dalpe, 1989; Remy et al., 1994). As such, the ability of plants to form AM must be under the control of mechanisms that have been conserved in new plant taxa as they appeared during evolution. This compatibility also implies that selective recognition processes in plants discriminate be? tween beneficial and harmful microorganisms and that the essential genetic determinants for AM establishment are com? mon to an extensive part of the plant kingdom. In contrast to their extremely wide host range and despite their ancient origins, only six genera of fungi belonging to the order Glomales of the Zygomycetes have evolved the ability to form AM (Morton and Benny, 1990). Interactions between an AM fungus and a plant begin when a hypha from a ger? minating soilborne spore comes into contact with a host root. Thi step is followed by induction of an appressorium, from which an infection hypha penetrates deep into the parenchyma cortex (Figure 1A), where interand intracellular proliferation of mycelium is intense. Here, fungal development culminates in the differentiation of intracellular haustoria, known as arb scules (Figure 1B). These fungal structures, which establish large surface of contact with the plant protopiast, are attrib? uted a key role in reciprocal nutrient exchange between the plant cells and the AM fungal symbionts (Smith and Smith, 1990). However, arbuscules are ephemeral structures, and an individual arbuscule reaches full development within several days, after which it begins to senesce (Alexander et al., 1988). AM development continues within a root system as the fungus spre ds to newly emerging roots. In this way, fungal coloniza? tion occurs concomitantly in different roots in an unsynchronized manner.

Nitrate depletion and pH changes induced by the extraradical mycelium of the arbuscular mycorrhizal fungus Glomus intraradices grown in monoxenic culture.

Abstract: The effect of the extraradical mycelium of the arbuscular mycorrhizal (AM) fungus Glomus intraradices Smith & Schenck on nitrate uptake and on the pH of the medium was studied in a monoxenic culture with tomato (Lycopersicon esculentum Mill. var. Vendor) roots obtained from root organ culture. The symbiosis was established in compartmented Petri dishes containing agar media amended with the pH indicator bromocresol purple. A pattern of pH changes was revealed as the symbiosis progressed in the media of the Petri dish compartments containing the dual, arbuscular-mycorrhizal fungi/root, culture as well as in the media of the hyphae, root-free compartments, in which the extraradical hyphae developed extensively, coming from the compartment containing the symbiosis. The colour changes in the media were measured spectrophotometrically, whilst maintaining the monoxenic conditions. The extraradical hyphae of G. intraradices strongly increased the pH of nutrient-free medium when supplied with nitrate, whereas the pH decreased m the absence of this N source. The hyphae developing from germinated spores and growing in axenic, nitrate-amended media did not induce any increase in pH. Nitrogen analysis revealed that a depletion of nitrate in the media accompanied increased pH. These results point towards an active uptake of nitrate by the extraradical mycelium of G. intraradices, probably coupled to a H+ -symport mechanism. The pH changes induced by AM fungal hyphae and the possible influence of the establishment of a functional symbiosis on these pH changes are discussed.

Glucanolytic Actinomycetes Antagonistic to Phytophthora fragariae var. rubi, the Causal Agent of Raspberry Root Rot.

Abstract: A collection of about 200 actinomycete strains was screened for the ability to grow on fragmented Phytophthora mycelium and to produce metabolites that inhibit Phytophthora growth. Thirteen strains were selected, and all produced (beta)-1,3-, (beta)-1,4-, and (beta)-1,6-glucanases. These enzymes could hydrolyze glucans from Phytophthora cell walls and cause lysis of Phytophthora cells. These enzymes also degraded other glucan substrates, such as cellulose, laminarin, pustulan, and yeast cell walls. Eleven strains significantly reduced the root rot index when inoculated on raspberry plantlets.

Polysaccharides in Fungi. XXXVI. Hypoglycemic Activity of a Polysaccharide (CS-F30) from the Cultural Mycelium of Cordyceps sinensis and Its Effect on Glucose Metabolism in Mouse Liver

Abstract: A polysaccharide (CS-F30) obtained from the cultural mycelium of Cordyceps sinensis showed potent hypoglycemic activity in genetic diabetic mice after intraperitoneal administration, and the plasma glucose level was quickly reduced in normal and streptozotocin-induced diabetic mice after intravenous administration. Administration of CS-F-30 to normal mice significantly increased the activities of hepatic glucokinase, hexokinase and glucose-6-phosphate dehydrogenase, although the glycogen content in the liver was reduced. Furthermore, CS-F30 lowered the plasma triglyceride level and cholesterol level in mice.

Hyphal interaction between Trichoderma harzianum and Sclerotinia sclerotiorum and its role in biological control

Abstract: Hyphal interactions between the mycoparasite Trichoderma harzianum (BAFC Cult. No. 72) and the soilborne plant pathogenic fungus Sclerotinia sclerotiorum were investigated in dual culture and in sterilized soil, by light and scanning electron microscopy. In dual culture, T. harzianum hyphae grew towards and coiled around the S. sclerotiorum hyphae. Dense coils of hyphae of T. harzianum and partial degradation of the Sclerotinia cell wall were observed in later stages of the parasitism. In sterile soil, conidia of T. harzianum germinated and the developing mycelium made contact with that of S. sclerotiorum, forming short branches and appressorium-like bodies which aided in holding and penetrating the host cell wall. An in vitro system was developed to test the ability of T. harzianum to control Sclerotinia wilt in cucumber and lettuce: coating seeds with T. harzianum conidia reduced the pre- and post-emergence effect of S. sclerotiorum in cucumber by 69 and 80%, respectively, and in lettuce by 46 and 72%, respectively. In the greenhouse, the disease caused by S. sclerotiorum in lettuce was reduced by treating seedlings with a peat-bran preparation of T. harzianum. Despite the non-significance of the reduction in disease, Trichoderma-treated lettuce seedlings were much more developed than controls. In sunflower, significant reductions (in the range of 68 to 84%) in disease incidence were obtained by incorporating the peat-bran T. harzianum preparation into the seedling rooting mixture. Hyphal mycoparasitism, rather than sclerotial parasitism, is suggested to be the mechanism by which T. harzianum controls S. sclerotiorum under these conditions.

Parasitism of sclerotia of Sclerotium rolfsii by Trichoderma harzianum : Ultrastructural and cytochemical aspects of the interaction

Abstract: The interaction between Trichoderma harzianum and sclerotia of the soilborne plant pathogen Sclerotium rolfsii was studied by scanning and transmission electron microscopy (SEM and TEM, respectively) to assess the potential role of enzymatic hydrolysis in the antagonistic process. SEM investigations revealed that hyphae of T. harzianum grew abundantly on the sclerotial surface and formed a dense branched mycelium that appeared to establish contact with the outer host cells through a thin mucilage. Observation of cross-sections of parasitized sclerotia by light microscopy showed that hyphae of the antagonist multiplied on the sclerotial surface and displayed the ability to penetrate the rind. Growth of the antagonist in the rind layer was mainly intracellular, and host-wall penetration was achieved by means of constricted hyphae. Ultrastructural observations showed that Trichoderma growth and development coincided with extensive host cell alterations, such as retraction and aggregation of the cytoplasm and vacuole breakdown. In the invaded outer rind cells, host cell walls apparently were not altered, as judged by their preserved structure. In contrast, cell breakdown due to host cell-wall disruption was observed more frequently in inner rind cells adjacent to medullary cells. Ingress of T harzianum hyphae in the medulla was characterized mainly by a change in the mode of growth from intra- to intercellular. Trichoderma hyphae did not penetrate the medullary cells, although the latter showed pronounced alterations, such as cytoplasm disorganization and aggregation. The use of wheat germ agglutinin/ovomucoid-gold complex for localization of chitin monomers resulted in regular labeling of both host and antagonist cell walls, even when sclerotia were massively colonized. Chitinolytic degradation at a distance from the site of Trichoderma penetration was never observed. There was no indication of cell-wall disorganization in either the host or the antagonist, as shown by the regular distribution of labeling, even in zones of penetration by constricted Trichoderma hyphae. In the medulla, gold labeling was regularly distributed over the thick host cell walls, even when the medullary cells showed obvious signs of disorganization. When ultrathin sections of parasitized sclerotia were incubated with the gold-complexed β-1,3-glucanase for localization of β-1,3-glucans, a regular distribution of gold particles was observed over the walls of both outer and inner rind cells, even when these exhibited a disorganized cytoplasm that was reduced to a few remnants of aggregated material. Incubation with gold-complexed lipoprotein lipase yielded a pattern of labeling similar to that obtained with gold-complexed β-1,3-glucanase. Gold particles were evenly distributed over the host cell walls in the rind layer.

A comparison of the extracellular enzyme activities of two ectomycorrhizal and a leaf‐saprotrophic basidiomycete colonizing beech leaf litter

Abstract: summary Activities of extracellular enzymes were determined in beech (Fagus sylvatica L.) leaf litter colonized by the litter decomposer Lepista nuda (Bull.: Fr.) Cooke or by vegetative mycelium from the mycorrhizal fungi Thelephora terrestris Ehrh.: Fr. or Suillus bovinus (L.: Fr.) O. Kuntze. Organic matter (OM) was buried for up to 6 months in plant containers in which mycorrhizal or non-mycorrhizal Pinus sylvestris L. seedlings were cultivated at a low rate of nutrient addition. After different periods of colonization the activities of phosphomonoesterase and protease, two enzymes involved in nitrogen and phosphorus mobilization, were determined in colonized and uncolonized litter. The activities of cellulase, β-xylosidase, β-glucosidase and polyphenol oxidase were investigated as indicators of the decomposition capacity of the fungi in the litter. Low activities of all enzymes tested were found in the uncolonized beech leaves. Phosphomonoesterase activity was high in litter colonized with L. nuda or S. bovinus, and was intermediate in the T. terrestris treatment. For all other enzymes the activities in the OM inoculated with the white-rot litter decomposer were considerably larger than those detected in litter colonized by ectomycorrhizal basidiomycetes. Cellulase activity was low in the control as well as in the mycorrhizal treatments. β-Xylosidase and β-glucosidase were detected in the litter with mycorrhizal mycelium, whereas polyphenol oxidase activity was only clearly increased in the S. bovinus treatment. These results demonstrate the low lignocellulase activity of both mycorrhizal fungi. This feature reduces the capacity of the mycorrhizal fungi to exploit fresh beech leaf litter, whose endogenous nitrogen is associated with or shielded by refractory compounds. The results are discussed in relation to the role of ectomycorrhizal fungi in nutrient cycling processes m temperate forest ecosystems.

Carbon and nitrogen allocation in ectomycorrhizal and non-mycorrhizal Pinus sylvestris L seedlings

Abstract: We studied carbon and nitrogen allocation in mycorrhizal and non-mycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in a semi-hydroponic system with nitrogen as the growth limiting factor. Three ectomycorrhizal fungi were compared: one pioneer species (Thelephora terrestris Ehrh.: Fr.) and two late-stage fungi (Suillus bovinus (L.: Fr.) O. Kuntze, and Scleroderma citrinum Pers.). By giving all plants in each treatment the same amount of readily available nitrogen, we ensured that the external mycelium could not increase the total nitrogen content of the plants, thereby guaranteeing that any change in carbon or nitrogen partitioning was a direct effect of the mycorrhizal infection itself. Carbon and nitrogen partitioning were measured at an early and a late stage of mycorrhizal development, and at a low and a high N addition rate. Although mycorrhizal seedlings had a higher net assimilation rate and a higher shoot/root ratio than non-mycorrhizal seedlings, they had a lower rate of shoot growth. The high carbon demand of the mycobionts was consistent with the large biomass of external mycelia and the increased belowground respiration of the mycorrhizal plants. The carbon cost to the host was similar for pioneer and late-stage fungi. Above- and belowground partitioning of nitrogen was also affected by mycorrhizal infection. The external mycelia of Scleroderma citrinum retained 32% of the nitrogen supplied to the plants, thus significantly reducing nitrogen assimilation by the host plants and consequently reducing their growth rate. By contrast, the external mycelia of T. terrestris and Suillus bovinus retained less nitrogen than the mycelia of Scleroderma citrinum, hence we attributed the decreased growth rates of their host plants to a carbon drain rather than a nitrogen deficiency.

Soil bacteria respond to presence of roots but not to mycelium of arbuscular mycorrhizal fungi

Abstract: Arbuscular mycorrhizal (AM) cucumber seedlings and uncolonized controls were grown in growth chambers which allowed separation of compartments with roots from compartments with the extraradical mycelium alone. Two fungi, Glomus invermaium Hall and G. caledonium (Nicol. and Gerd.) Trappe and Gerdemann, were used. Bacterial numbers (direct and viable count) and activities (thymidine incorporation) were highest in the root compartment, but were not affected by the AM mycelium after 30 days of plant growth. The soil was stored after harvest for 16 d at 13 degrees C to study the effect of disconnected mycorrhizal hyphae on bacterial activity. This treatment increased bacterial activity in mycorrhizal treatments compared to non-mycorrhizal control soils. The highest increase was found in the root compartment. The bacterial community structure was studied by analyzing the phospholipid fatty acid (PLEA) pattern. The bacteria specific PLFAs cy17:0 and cy19:0 increased in both experiments in the root compartments. The PLFAs 15:0 and 17:0, which are usually considered to be bacteria specific, also increased due to the presence of roots, but it was shown that these fatty acids were present in aseptically grown cucumber roots, and thus not bacteria specific. No bacterial PLFAs were affected by the presence of mycorrhiza. Copyright (C) 1996 Elsevier Science Ltd (Less)

Mycoparasitism of the extramatrical phase of Glomus intraradices by Trichoderma harzianum

Abstract: In the present study, the interaction between the saprophytic fungus Trichoderma harzianum and the arbuscular mycorrhizal (AM) fungus Glomus intraradices was studied by transmission electron microscopy (TEM) to delineate precisely the relationship established between both partners. An axenic system, divided into four compartments, proved useful for studying the interaction between T. harzianum and the extramatrical phase of G. intraradices. This experimental model, based on root-organ culture to obtain typical mycorrhizal infections, was selected as a reliable means of obtaining mycorrhizal spores and mycelium in root-free compartments. TEM observations of samples from the interaction region showed that hyphae of T. harzianum proliferated abundantly at the spore surface and penetrated the thick host wall through local hydrolysis of the wall polymers. Hyphae of the antagonist also were seen in the subtending hyphae of the AM fungus, and they grew actively in the main host hyphae. This massive colonization was associated with marked cell damage, involving partial to complete disorganization of the cytoplasm, which led in most cases to loss of the protoplasm and apparent bursting of the main hyphae of G. intraradices, resulting in the release of the actively proliferating Trichoderma hyphae. At an advanced stage of the colonization process, the main hyphae of G. intraradices were perforated in many places. The use of wheat germ agglutinin/ovomucoid-gold complex for the localization of chitin monomers resulted in regular labeling of the host cell walls even when spores, subtending hyphae, and main hyphae of G. intraradices were colonized massively. Chitinolytic degradation was seen only in areas adjacent to the sites of Trichoderma penetration. According to our observations, the interaction between T. harzianum and G. intraradices involves the following events : (i) recognition and local penetration of the antagonist into mycorrhizal spores ; (ii) active proliferation of antagonist cells in mycorrhizal hyphae; and (iii) release of the antagonist through moribund hyphal cells.

Facilitation of plant phosphate acquisition by arbuscular mycotrhizas from enriched soil patches

Abstract: summary Effects of arbuscular mycorrhizas (AM) on plant exploitation of soil nutrient heterogeneity were studied with non-mycorrhizal and mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in two-compartment containers. A central cylindrical plant compartment was separated from an outer hyphal compartment by two layers of stainless-steel screen with a 2 mm air gap between the screen layers. Patchy or uniform nitrate (NO2−) and phosphate (P) distribution patterns were created in the outer compartment. Only AM hyphae could cross the double-screen barrier to access those nutrients. Mycorrhizal plants acquired significantly more labelled P in both the patchy- and the uniform-nutrient treatments than did non-mycorrhizal plants. Mycelia in root-free soil delivered similar amounts of P from the more distant rich patches to mycorrhizal plants as from the uniform and more proximate labelling. The uptake of a more mobile and abundant element, nitrate, was not affected significantly by either mycorrhizal infection or by nutrient distribution patterns in the root-free soil. Despite a lower root:shoot mass ratio, mycorrhizal plants had significantly greater shoot phosphorus concentration than did nonmycorrhizal plants. There was no significant difference in P uptake or phosphorus concentration between the two nutrient distribution patterns for mycorrhizal plants, indicating that AM hyphae can explore the root-free soil for available P and transport it to host plants equally well when P was distributed in either patchy or uniform patterns in the root-free soil.

Development of fungal inocula for bioaugmentation of contaminated soils

Abstract: This report describes novel fungal inocula for bioaugmentation of soils contaminated with hazardous organic compounds. The inocula are in the form of pelleted solid substrates coated with a sodium alginate suspension of fungal spores or mycelial fragments and incubated until overgrown with the mycelium of selected lignin-degrading fungi. The organisms evaluated were Phanerochaete chrysosporium (BKM F-1767, ATCC 42725), P. sordida (HHB-8922-Sp), Irpex lacteus (Mad-517, ATCC 11245), Bjerkandera adusta (FP-135160-Sp, ATCC 62023), and Trametes versicolor (MD-277). The pelleted fungal inocula resisted competition and proliferation from indigenous soil microbes, were lower in moisture content than current fungal inocula, and had sufficient mechanical strength to allow handling and introduction into the soil without a change in the mechanical consistency of the pellets. Inoculated at a rate of 3% in artificially contaminated nonsterile soil, I. lacteus, B. adusta, and T. versicolor removed 86, 82, and 90%, respectively, of the pentachlorophenol in 4 weeks. A mathematical model was developed to explain moisture distribution in a hydrogel-coated pelleted substrate.

Physiological heterogeneity within fungal mycelia: an important concept for a functional understanding of the ectomycorrhizal symbiosis.

Abstract: Individual mycelia of filamentous fungi display considerable heterogeneity at the physiological level. Important physiological processes such as nutrient absorption, extracellular enzyme secretion and solute translocation occur differentially within an individual mycelium, and vary according to spatio-temporal changes in patterns of gene expression as the mycelium develops and senesces. In ectomycorrhizal (ECM) fungi, gene expression appears to be strongly influenced by interaction with the soil environment and the host root. The ECM mycelium is thus a complex and dynamic entity wherein discrete regions display particular physiological attributes. Physiological heterogeneity is important in the overall functioning of the symbiosis. In the particular case of movement of phosphorus from soil to host root in the ECM symbiosis, heterogeneity might provide the driving force for the integrated processes of absorption, translocation and transfer. It is suggested that it is only by considering the sum of the seemingly disparate physiological processes within the heterogeneous mycelium that mycorrhizal functioning can be fully understood.

Facilitation of plant phosphate acquisition by arbuscular mycorrhizas from enriched soil patches. II. Hyphae exploiting root-free soil

Abstract: Effects of arbuscular mycorrhizas (AM) on plant exploitation of soil nutrient heterogeneity were studied with non-mycorrhizal and mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in two-compartment containers. A central cylindrical plant compartment was separated from an outer hyphal compartment by two layers of stainless-steel screen with a 2 mm air gap between the screen layers. Patchy or uniform nitrate (NO 3 - ) and phosphate (P) distribution patterns were created in the outer compartment. Only ANI hyphae could cross the double-screen barrier to access those nutrients. Mycorrhizal plants acquired significantly more labelled P in both the patchy- and the uniform-nutrient treatments than did non-mycorrhizal plants. Mycelia in root-free soil delivered similar amounts of P from the more distant rich patches to mycorrhizal plants as from the uniform and more proximate labelling. The uptake of a more mobile and abundant element, nitrate, was not affected significantly by either mycorrhizal infection or by nutrient distribution patterns in the root-free soil. Despite a lower root :shoot mass ratio, mycorrhizal plants had significantly greater shoot phosphorus concentration than did nonmycorrhizal plants. There was no significant difference in P uptake or phosphorus concentration between the two nutrient distribution patterns for mycorrhizal plants, indicating that AM hyphae can explore the root-free soil for available P and transport it to host plants equally well when P was distributed in either patchy or uniform patterns in the root-free soil.

Growth and mineral nutrition of non- mycorrhizal and mycorrhizal Norway spruce (Picea abies) seedlings grown in semi-hydroponic sand culture I. Growth and mineral nutrient uptake in plants supplied with different forms of nitrogen

Abstract: Growth, nitrogen uptake and mineral nutrient concentrations in the plant tissues were determined in non-mycorrhizal and mycorrhizal Norway spruce (Picea abies (L.) Karst.) seedlings grown under controlled conditions in a semi-hydroponic culture system with quartz sand as substrate and a percolating nutrient solution. The culture system allowed the determination of nutrient uptake rates in mycorrhizal root systems with an intact extramatrical mycelium. The rate of infection of the roots by the mycorrhizal fungi Pisolithus tinctorius and Laccaria laccata was high but the rate of infection by Paxillus involutus was low. When supplied with ammonium nitrate, the d. wt of the roots and particularly of the shoots was significantly lower in mycorrhizal than in non-mycorrhizal plants. Despite the lower root d. wt, the number of root tips and the root branching ratio (number of root tips per unit root length) were significantly higher in mycorrhizal plants infected with L. laccata and P. tinctorius than in non-mycorrhizal plants. The depletion of ammonium in the external solution was faster than the depletion of nitrate. Nitrate uptake rates increased at ammonium concentrations below 400 μM. The maximal N uptake rates (V max ), calculated after Lineweaver-Burk, were significantly higher for ammonium than for nitrate. The N uptake rates did not differ significantly between non-mycorrhizal and mycorrhizal plants. The concentrations of N, P, K, Ca and Mg tended to be higher in the smaller mycorrhizal than in the larger non-mycorrhizal plants. A significant increase in mineral nutrient concentration in mycorrhizal compared with non-mycorrhizal plants was found only for N concentrations in the needles of mycorrhizal plants infected with P. tinctorius. When they were supplied with ammonium ((NH 4 ) 2 SO 4 ) as source of N, but not when they were supplied with nitrate (KNO 3 ), the d. wt was lower in mycorrhizal plants infected with P. tinctorius than it was in non-mycorrhizal plants. Therefore, N uptake rates were increased in mycorrhizal plants with P. tinctorius only when they were supplied with ammonium but not with nitrate. The insignificant differences in uptake rates of N, P, K, Ca and Mg between non-mycorrhizal and mycorrhizal plants indicate that at unlimited spatial nutrient availability the contribution of the extramatrical mycelium to nutrient uptake by mycorrhizal plants was small. It is suggested that the decreased growth of mycorrhizal plants is due to the demand of the mycorrhizal fungus for photosynthates, i.e. source limitation.

Dynamics of lead accumulation in mycorrhizal and non-mycorrhizal Norway spruce (Picea abies (L.) Karst.)

Abstract: Twelve-week-old seedlings of Norway spruce (Picea abies (L.) Karst), non-mycorrhizal or mycorrhizal with Laccaria laccata, Paxillus involutus or Pisolithus tinctorius were exposed to 5 μM Pb for either 32 or 42 days in a quartz sand-nutrient solution system. Ultrathin sections of mycorrhizal and non-mycorrhizal short roots were examined by X-ray microanalysis. After 42 days Pb treatment, the Pb content of the cortex cell walls was lower in the non-mycorrhizal short roots and in the P. involutus mycorrhizae than in the mycorrhizae of L. laccata or P. tinctorius. The Pb content of the cell walls of the hyphal mantle was higher in P. involutus than in L. laccata or P. tinctorius. The short term experiment over 32 days showed that the Pb content of the cortex cell walls strongly increased during the first 16 days in the non-mycorrhizal roots and the L. laccata mycorrhizae, whereas it increased more slowly in the P. involutus mycorrhizae. After 32 days Pb treatment, the Pb content in the cortex cell walls in the P. involutus mycorrhizae was similar to that in the non-mycorrhizal roots. P. involutus also decreased Pb translocation from the roots to the stems. Mycorrhizal infection was not affected by Pb but with P. involutus, the amount of extramatrical mycelium was reduced by 50% on day 32 compared to day 16. The extramatrical mycelium of L. laccata was not reduced by Pb. It is concluded that ectomycorrhizal fungi differ in their effect on Pb accumulation in the roots of Norway spruce. The binding capacity of the extramatrical mycelium seems to be an important factor.

Growth and mineral nutrition of non‐mycorrhizal and mycorrhizal Norway spruce (Picea abies) seedlings grown in semi‐hydroponic sand culture

Abstract: summary In seedlings of Norway spruce (Picea abies (L.) Karst.), grown in semi-hydroponic sand culture, mycorrhizal infection decreased growth (Eltrop & Marschner, 1996). Possible reasons for this growth depression were investigated in the present study by comparing the plant and fungal biomass distribution and carbon partitioning between non-mycorrhizal and mycorrhizal (Pisolitlius tinctorius) plants supplied with ammonium or nitrate as source of N. Despite the high mycorrhizal infection rate (55–71% of total root tips), the amount of fungal biomass in roots and extramatrical mycelium of mycorrhizal plants accounted for less than 3% of plant dry matter and was significantly lower in nitrate- than in ammonium-supplied plants. The CO2 assimilation rates were higher in mycorrhizal than in non-mycorrhizal plants supplied with ammonium as well as those supplied with nitrate. High light intensity considerably increased CO2 assimilation rates. The respiration rates of the intact root systems were significantly increased in ammonium-supplied mycorrhizal plants compared with non-mycorrhizal plants. The amount of CO2 lost in root respiration as a percentage of the amount of CO2 gained in photosynthesis (respiratory quotient), ranged from 49.3% at 30°C root zone temperature and low light intensity (290 μmol m−2 S−1) to 11.7% at 10 °C and high light intensity (990 μmol m−2 s−1). In ammonium-supplied plants grown at 22 °C and low light intensity, the proportion of carbon lost by root respiration was significantly higher in mycorrhizal than in non-mycorrhizal plants. This increase in root respiration was of the same order of magnitude (7.4 %) as the decrease in dry matter production by mycorrhizal plants (10.1 %). In nitrate-supplied plants, no significant difference in the respiratory quotient was found between non-mycorrhizal and mycorrhizal plants. The respiration rate per unit d. wt of the fungal mycelium was estimated to account for 31.3 % (ammonium supply) and 8.3 % (nitrate supply) of that of the total mycorrhizal root system although the dry weight accounted for only 4. % (ammonium supply) and 2.5 % (nitrate supply). Accordingly, the respiration rate was calculated to be 11.1 times higher with ammonium supply, and 3.4 times higher with nitrate supply, than that of the root tissue. The carbohydrate concentrations in shoots and roots were not consistently different between non-mycorrhizal and mycorrhizal plants. It was concluded that increased root respiration was mainly responsible for the growth reduction in mycorrhizal compared with non-mycorrhizal plants, whereas the production of fungal biomass in the extramatrical mycelium of mycorrhizal plants was of minor importance.

Cultural Studies On Soil Nematodes and Their Fungal Hosts

Abstract: In laboratory experiments survival, feeding and reproduction of nematodes in cultures with mycorrhizal and saprophytic fungi were investigated. Nematodes extracted from the organic layer of a spruce forest soil were inoculated to fungal plates. The fungal feeder Aphelenchoides saprophilus was the most successful species to multiply. With mycorrhizal fungi as a food source its population developed faster and to a greater extent than it did with saprophytic fungal species. The grazing of A. saprophilus reduced mycelial weight and fungal growth rate. Similar effects are likely to occur in the field, and can influence mycorrhizal development or affect competition between soil fungi. Besides A. saprophilus, the saprophagous nematode Acrobeloides nanus reproduced well in cultures with mycorrhizal fungi. There may be an element of substrate ingestion or grazing on fungal hyphae for some bacterial feeding nematodes.

Interactions between a mycophagous Collembola, dry yeast and the external mycelium of an arbuscular mycorrhizal fungus

Abstract: A plant growth system with root-free hyphal compartments was used to examine the interactions between a mycophagous Collembola (Folsomia candida Willem), dry yeast and an arbuscular mycorrhizal (AM) fungus [Glomus caledonium (Nicol. & Gerd.) Trappe and Gerdemann] in terms of Collembola reproduction, AM-hyphal length and AM-hyphal P transport. Collembola reproduction was unaffected by AM mycelium, but a supplement of dry yeast increased the Collembola population size. The addition of dry yeast increased AM-hyphal P transport by increasing hyphal length. Collembola without yeast affected neither AM-hyphal growth nor AM-hyphal P transport, whereas Collembola with yeast decreased AM-hyphal P transport by 75% after 8 weeks. The hyphal density of G. caledonium remained unaffected by Collembola except after 4 weeks in combination with yeast, when a 33% reduction was observed. The results of this experiment show that the interaction between F. candida and the external mycelium of G. caledonium is limited under the conditions imposed.

Effects of N-free fertilization on ectomycorrhiza community structure in Norway spruce stands in Southern Sweden

Abstract: The application of N-free fertilizer (i.e. lime combined with nutrients such as P, Ca, K and Mg) has been suggested as one way of compensating for nitrogen-caused eutrophication and losses of base cations due to atmospheric pollution. To study the effects of such a treatment on mycorrhizal fungi, fine-root samples were collected from the LFH-layer in four Norway spruce stands in southern Sweden. One stand was part of a larger experiment (Skogaby) and had four replicates. It was fertilized twice in 1988–89 (P:K:Ca:Mg:S 48:43:218:46:75 kg ha-1), and sampling was carried out once yearly during 1991–93. The other three stands were fertilized once in 1988–89 (P:K:Ca:Mg:S|25:62:33:12:54 kg ha-1) and sampled in 1992. Ectomycorrhizal fine-roots were classified into morphotypes on the basis of the structure and colours of their external hyphae and fungal mantle. The fungal biomass was estimated in 1992 using ergosterol analysis. In Skogaby, N-free fertilizer had no apparent effects on fungal biomass or on the total number of ECM types. Similar results were obtained for the other three stands. Previously reported 50% reductions in sporocarp production on the fertilized plots at Skogaby can probably be explained by a decrease in carbon allocation to the roots and by a decline in the abundance of a single morphotype which accounted for 3% of the total number of root tips, but ca. 30% of the sporocarp biomass in the control plots in the present study. It is concluded that moderate levels of N-free fertilization are not likely to drastically affect the community structure of the dominating ectomycorrhizal fungi. This result should be interpreted with some caution, however, since it remains to be determined whether the fertilizer treatments affect the function of the nutrient-absorbing soil mycelium of the mycorrhizal fungi.

Bronchial Mucoid Impaction Due to the Monokaryotic Mycelium of Schizophyllum commune

Abstract: We report, to our knowledge, the first case of mucoid impaction of the bronchi due to a hypersensitivity reaction to the monokaryotic mycelium of Schizophyllum commune. The patient was hospitalized because of mild asthma attacks, persistent cough, peripheral eosinophilia, and "gloved finger" shadows on a chest roentgenogram. Bronchoscopic examination disclosed mucoid impactions that consisted of accumulations of eosinophils, Charcot-Leyden crystals, and nondichotomously branched hyphae in B3, B9, and B10 of the left lung. Cultures of the mucous plugs and sputum samples yielded white, felt-like mycelial colonies that were later identified as the monokaryotic mycelium of S. commune by use of mating tests with established monokaryotic and dikaryotic strains of S. commune. The results of tests for serum antibody to S. commune cytosol antigen were positive. Repeated bronchoscopies for performing bronchial toilet were effective in removing the mucous plugs and relieving the patient's symptoms. We suggest that the monokaryotic mycelium of S. commune should be considered as one of the fungi that can cause hypersensitivity-related lung diseases.

Highly efficient homologous integration via tandem exo-beta-1, 3-glucanase genes in the common mushroom, Agaricus bisporus.

Abstract: Homologous integration was studied in the common mushroom, Agaricus bisporus, using a plasmid (pHAG3-1) carrying the hygromycin-resistance gene and a 3.2-kb genomic fragment from A. bisporus. Homologous integration was found in 30–60% of the transformants obtained with pHAG3-1 linearized at three different positions within the homologous sequence, generating either blunt, 5′- or 3′-protruding ends. The genomic fragment was found to contain two homologous open reading frames in tandem, which showed 60% similarity to exo-β-1,3-glucanases from Saccharomyces cerevisiae and Candida albicans. The level of the corresponding mRNA is low in the vegetative mycelium and relatively high in fruiting bodies. In the vegetative mycelium of a transformant with tandemly integrated pHAG3-1 plasmids at the homologous position, exoglucanase mRNA was strongly increased without any apparent effect on growth rate or morphology.

Mycelium-bound lipase from a locally isolated strain of Aspergillus flavus link: pattern and factors involved in its production

Abstract: Aspergillus flavus produces a lipase (EC 3.1.1.3) which is partly bound to the mycelium during growth. The production of the mycelium-bound lipase is concomitant with growth, and declines when growth ceases. Maximum productivity of the enzyme is obtained when the culture is incubated at 30°C, an initial culture pH of 6·5 and with 2% (w/v) each of corn oil and yeast extract as carbon and organic nitrogen source. Yeast extract affects not only the production of lipase but also the secretion of proteases into the culture medium. Production of the latter enzymes, which inactivate the free lipase, is enhanced by adding yeast extract (1–2%, w/v) to the culture medium. However, at 5% (w/v) yeast extract concentration, proteolytic activity is not detected and consequently, the activity of free lipase may easily be measured. Free lipase activity can easily be detected when 0·001 mol dm−3 EDTA is added to the culture medium. The presence of the chelating agent enhances the production and maintains the stability of the extracted mycelium-bound lipase.