bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of disease in wild plant populations and the evolution of pathogen aggressiveness
Authors: JAROSZ ANDREW M. , DAVELOS ANITA L. 
Published: April 2006

SUMMARYFungal pathogens can alter host fitness by affecting a plant's ability to survive, reproduce, compete, grow or defend itself against herbivores and other parasites. However, infections need not have uniformly negative effects, and the outcome of a fungus‐plant interaction can range from strongly parasitic, through commensalistic, to mutualistic. The outcome of the interaction is determined by characteristics of the fungus and plant, as well as ecological conditions.Damping off and root rot diseases severely reduce plant survivorship. These pathogens appear to be highly aggressive, a trait that may be evolutionarily constrained because of the necrotrophic infection habit. Incidence is locally high with patch size being variable. Canker and wilt pathogens reduce plant survivorship and growth, and tend to be highly aggressive. Two diseases within this group, chestnut blight and Dutch elm disease, have caused sustained highly destructive pandemics on their hosts. Neither pathogen appears to be evolving towards genetically based reduced aggressiveness despite the fact that disease incidence is near 100 % over a wide area. Less aggressive strains may not be selectively favoured because plants can be multiply infected, which would allow more aggressive strains to invade trees previously infected by less aggressive strains. Obligate foliar diseases can affect plant fitness by reducing survivorship, reproduction, growth or competitive ability of the host. However, overall effects are often slight and the relationship between plant and pathogen range from strongly parasitic to nearly commensalistic. Disease incidence is highly variable across space and time, and much of the variability appears to be influenced by climatic and environmental variables. Non‐systemic foliar diseases reduce plant reproduction, but some interactions may be nearly commensalistic because of low seed set in healthy individuals. Thus, disease effects are minimized in environments where reproduction by seed is not important. Systemically infecting pathogens can alter plant survivorship, reproduction, growth, competitive ability and susceptibility to herbivores. The effects can be positive as well as negative, and the net outcome of the interaction can range from strongly parasitic to unconditionally mutualistic. Trends within this group support Clay's New Function Hypothesis that pathogens can reduce their aggressiveness by acquiring new functions which increase plant fitness, and not by the amelioration of the original disease symptoms.

Contents

Summary
371

I.
Introduction
372

II.
Incidence and effects of pathogens
373

III.
Conclusions
384

IV.
Acknowledgements
385

V.
References
385
Deposition of nitrogen in vacuolar bodies of Cenococcum geophilum Fr. mycorrhizas as detected by electron energy loss spectroscopy
Authors: KOTTKE I. , HOLOPAINEN T. , ALANEN E. , TURNAU K. 
Published: April 2006

SUMMARYNitrogen fertilization of potted Pinus sylvestris L. seedlings growing in forest humus was carried out using two different concentrations of ammonium sulphate and ammonium chloride, corresponding to 50 and 100 kg N ha‐1. Cenococcum geophilum Fr. mycorrhizas were collected from the root systems of the seedlings and investigated by light and transmission electron microscopy. The number of vacuolar osmophilic bodies in the mantle hyphae significantly increased after fertilization with both ammonium salts. The bodies were analyzed by electron energy loss spectroscopy. Nitrogen and phosphorus content increased following ammonium sulphate fertilization, but decreased with ammonium chloride. Cytoplasmic injury was observed in the hyphae in both ammonium chloride treatments but only in the higher ammonium sulphate treatment. It is hypothesized that the bodies have a transient storage and N‐filtering function.
Enzyme activities of the internal hyphae and germinated spores of an arbuscular mycorrhizal fungus, Gigaspora margarita Becker & Hall
Authors: SAITO MASANORI 
Published: April 2006

SUMMARYA method for isolation of metabolically active internal hyphae from arbuscular mycorrhizas of onion (Allium cepa) is described. Roots of onion plants colonized by Gigaspora margarita were treated with a digestion solution containing cellulase and pectinase for 1 h at 30 °C, then homogenized with a Waring blender at low speed. The internal hyphae were collected from the homogenate by centrifugation on a discontinuous gradient of Percoll, then purified further by filtration. Enzyme histo chemical staining showed that the collected internal hyphae had active succinate dehydrogenase (SDH), alkaline and acid phosphatases (ALP, ACP). Specific activities (protein basis) of several enzymes in a crude extract of the internal hyphae were compared to those of axenically germinated spores of G. margarita. The specific activities of hexokinase, and of the enzymes involved in phosphate metabolism (ALP, ACP) and the TCA cycle (SDH, malate dehydrogenase) were much greater in the internal hyphae than in the germinated spores. The specific activity of phosphofructokinase was similar in both. By contrast, the specific activity of glucose‐6‐phosphate dehydrogenase was higher in the germinated spores. The metabolic change from non‐symbiotic to symbiotic status of the fungus is discussed in relation to these results.
Electrical currents associated with arbuscular mycorrhizal interactions
Authors: BERBARA R. L. L. , MORRIS B. M. , FONSECA H. M. A. C. , REID B. , GOW N. A. R. , DAFT M. J. 
Published: April 2006

SUMMARYElectrical currents associated with the plant‐fungus interaction between roots and an arbuscular mycorrhizal (AM) fungus Gigaspora margarita were measured with a one‐dimensional vibrating probe. Uninfected roots of clover (Trifolium repens L. cv. New Zealand White) and carrot (Daucus carota L. cv. Nantes) had an inwardly directed positive electrical current at the apical meristematic and elongation zones and an outward flow at the mature non‐growing regions. The current profile of endomycorrhizal colonized roots did not differ markedly in magnitude or pattern compared with non‐colonized roots of an equivalent stage of development. A small current was measured circulating around and through single mycorrhizal azygospores of G. margarita. Germ tubes emerged within the zone of outward current and an inward current was found at the hyphal tip. When roots were colonized by the fungus an inward current was induced at the point of hyphal contact with the host root. This current declined over a period of 6 d. Because hyphal penetration of plant roots by AM fungi does not rupture the plant host membrane we propose that the host current is not the result of wounding but is induced by fungal elicitors at the infection court.
Ericoid mycorrhizas and rhizoid‐ascomycete associations in liverworts share the same mycobiont: isolation of the partners and resynthesis of the associations in vitro
Authors: DUCKETT JEFFREY G. , READ DAVID J. 
Published: April 2006

SUMMARYThe hypothesis was tested that rhizoids of leafy liverworts of the families Lepidoziaceae, Calypogeiaceae, Cephaloziaceae and Cephaloziellaceae can be infected by the aseomycetous fungal endophyte Hymenoicyphus ericae which forms ericoid mycorrhiza with the major ericaceous genera Calluna, Erica, Rhododendron and Vaccinium. The extent of the specificity of any such association was also examined by growing the liverworts with pure cultures of the putative ascomycetous ericoid endophyte Oidiodendron, with the basidiomycetous endophyte of orchids, Ceratobasidium cornigerum, and with several ectomycorrhizal fungi.It was confirmed that the members of these liverwort families tested, most of which are associated in nature with ericaceous plants, were readily infected by H. ericae, as well as by isolates obtained from the liverworts themselves. The latter, when used to challenge aseptically grown seedlings of the ericaceous genera on water agar, produced typical ericoid mycorrhiza. Neither the Oidiodendron isolates nor the orchid or ectomycorrhizal fungi infected the liverworts, and all failed to reproduce the characteristic swelling of the rhizoid tips which is seen in nature and in plants inoculated with H. ericae.The results provide a major extension of the likely host range of H. ericae and may have considerable significance for both groups of plants which, as a consequence of sharing the same endophyte, have the potential to act as sources of inoculum for each other in nature. The possible physiological and ecological impacts of the association for both liverwort and ericaceous hosts are discussed.
Real‐time measurement of uptake and translocation of 137Cs within mycelium of Schizophyllum commune Fr. by autoradiography followed by quantitative image analysis
Authors: GRAY S. N. , DIGHTON J. , OLSSON S. , JENNINGS D. H. 
Published: April 2006

SUMMARYA new technique, autoradiography followed by quantitative image analysis, provides a powerful, non‐destructive method for measurement of radiolabel distribution and translocation throughout: fungal mycelia. Using this technique radio caesium was found to be translocated by bulk flow in actively expanding mycelium of S. commune but by diffusion in established mycelium in microcosms. Differentiation of hyphae to form primordia in preparation for basidiocarp production was found to introduce heterogeneity into the distribution of radio caesium in mycelia which could later be reversed by diffusion. Mycelium of S. commune was not conservative for radiocaesium, losing significant amounts to the medium; it is suggested that binding to soil particles may be more significant in terms of long‐term retention of this radionuclide in the environment. These processes may account in part for the high and variable concentrations of radiocaesium found in mushrooms in the environment.
Carbon translocation in mycelial cord systems of Phanerochaete velutina (DC: Pers.) Parmasto
Authors: WELLS J. M. , BODDY LYNNE , EVANS R. 
Published: April 2006

SUMMARYMovement of radiotracer was monitored in mycelial cord systems developed from wood block inocula, pre‐colonized by Phanerochaete velutina (DC: Pers.) Parmasto grown on unsterile soil. In short‐term studies, reproducible but low‐level loading of radiotracer was observed which was independent of the extent of cord systems. Carbon translocation velocities ranged from 132 to 336 cm h‐1, whilst fluxes were estimated to range from 35 to 66 nmol cm‐2 h‐1 (as glucose). When cord systems were supplied with a range of potential carbon resources as baits considerable movement of carbon was detected over 9 wk. More than 80 % of exogenously supplied carbon was retained in resource units rather than being allocated to extra‐resource mycelium. The direction and extent of carbon movement, and partitioning of decay between inocula and baits within cord systems, was dependent upon the type and size of bait and whether or not combinations of baits included wood pre‐colonized by other sapro trophic fungi. There was evidence for coordinated use of resources within cord systems and that carbon movement was not a function of mycelial growth. Respiratory carbon losses were greatest when baits included sterile leaf litter packs and least when sterile wood baits were supplied. The results are discussed in terms of nutrient conservation and cycling in cord systems.
Structure and function of the ectomycorrhizal association between Paxillus involutus (Batsch) Fr. and Betula pendula Roth.
Authors: BRUN A. , CHALOT M. , FINLAY R. D. , SÖDERSTRÖM B. 
Published: April 2006

SUMMARYDetailed examination of the structural and functional integration taking place during mycorrhiza formation necessitates rapid and aseptic synthesis of uniform mycorrhizal structures at well‐defined stages of development. A system is described for formation of ectomycorrhizas between Betula pendula Roth, and Paxillus iiwolulus (Batsch) Fr. Small sterile seedlings were placed directly on fungal colonies growing on cellophane covered agar plates. Microscopic examination during the course of development indicated an initial rapid colonization of the roots and formation of a fully developed mantle within 2–4 d. Hartig net formation was evident after 8 d of contact and involved a transition from a para epidermal organization to a mature peri epidermal Hartig net after 15 d of contact. Using a standard fungal growth medium, formation and development of mycorrhizas were not greatly affected by changes in the overall concentrations of nitrogen and phosphorus but changes in the ratio of nitrogen to phosphorus had strong effects on development and mycorrhiza formation was completely suppressed when the ratio of nitrogen to phosphorus was increased. These differences were not related to the effects of nitrogen or phosphorus on linear growth of the fungus.
Extraction of conifer waxes as the basic principle of Härtel's turbidity test
Authors: PFEIFHOFER HARTWIG W. 
Published: April 2006

SUMMARYHartel's turbidity test (‘Trübungstest’) has been one of the most widely used diagnostic tests for air pollution injury. It relies on the extraction of lipophilic substances into an aqueous suspension, whose light absorption is used as an indication of exposure to pollution. As a first step towards a better understanding of the test's reaction mechanism, the identity of the turbidifying compounds was analyzed. For that purpose, needles of Norway spruce [Picea abies (L.) Karst.] were extracted with boiling water following the standardized procedures of the turbidity test. The lipids were recovered by centrifugation and fractionated by preparative chromatography. The isolated compounds were identified by gas chromatography (GC), GC‐mass spectrometry and comparison with authentic samples. The samples were hydrolyzed with methanolic HCl. Quantitative analysis of the lipid composition was completed by GC without prior class separation. The composition of the turbidifying substances was equal to control samples of epicuticular waxes of Norway spruce needles, with w‐hydroxy‐n‐alkanoic acids, n‐alkanoic acids, α,ω‐alkanediols, and the secondary alcohol 10‐nonacosanol as the predominant compound classes. The content of unsaturated fatty acids (C18:1, C18:2, C18:3), which are characteristic constituents of membrane lipids, was negligible. Extraction of needles with sodium oxalate, which resulted in enhanced turbidity, was connected only with an enhanced recovery of extracted epicuticular lipids, whereas the lipid composition showed only minimal variation. Therefore, the reaction mechanism of Härtel's turbidity test seems to be solely controlled by factors that influence the interaction of epicuticular wax compounds with water. The previously published supposition, that filtration of compounds through the epidermal cell wall should be the main principle of the test's reaction mechanism, could not be confirmed.
Clonal integration between parent and branch stolons in white clover: a developmental study
Authors: KEMBALL W. D. , MARSHALL C. 
Published: April 2006

SUMMARYThe distribution of 14C‐assimilate from single leaves on the main stolon and branch stolons was investigated at different stages of plant development in a small‐leaved wild genotype of Trifolium repens. A widespread distribution pattern was observed with assimilate moving from source leaves to all plant parts, with the closest sinks receiving the greatest proportion of assimilate. A high proportion of assimilate was translocated to the branch stolon originating at the same node as the 14C‐treated leaf, thus indicating a close vascular linkage between source and sink. Branch stolons were shown to import and export simultaneously large quantities of assimilate at all stages of development investigated. Overall the pattern of assimilate distribution on the main stolon and from equivalent positioned leaves on a basally positioned branch stolon was very similar at all stages of plant development. The high degree of clonal integration and reciprocal assimilate exchange in T. repens are discussed in relation to growth in pastures.
Tip growth in root hair cells of Sinapis alba L.: significance of internal and external Ca2+ and pH
Authors: HERRMANN ALMUT , FELLE HUBERT H. 
Published: April 2006

SUMMARYIn Sinapis root hair cells, tip growth has been measured and studied with different electrophysiological techniques. Applying ion‐selective microelectrodes, we measured 452–776 nM free [Ca2+] in the tip, which is about three times the concentration found in the base. The cytosolic pH of 7.1–7.3 in the tip is statistically not different from values measured in the base. The cells react to changes in external [Ca2+] between 0.01 and 10 mM with transient changes in growth intensity and cytosolic [Ca2+]: increased external [Ca2+] elevates cytosolic [Ca2+] followed by a growth burst. Whereas external [Ca2+] lower than 1 μM is inhibitory to steady state tip growth, concentrations up to 30 mM are not. Vibrating probe analysis reveals inwardly directed net Ca2+‐currents in the tip only. The calcium channel antagonists nifedipine and La3+ decrease cytosolic free [Ca2+], inhibit the inwardly directed Ca2+‐current and tip growth. Dibromo‐BAPTA, injected into the cells, also decreases cytosolic [Ca2+] and inhibits growth, but only marginally depolarizes the cells. Abrupt changes in external pH between 5 and 9 affect cytosolic pH and transiently inhibit tip growth, regardless of the direction of the pH‐shift. Acetic acid and NH4Cl both inhibit tip growth only, when the cytosolic pH is shifted from its steady state value. Tip growth is inhibited in the presence of the ATPase inhibitors DCCD, vanadate and erythrosin B. We argue that several Ca2+‐ and pH‐related processes are pivotal for tip growth in root hairs: with respect to Ca2+, these are an inwardly directed Ca2+‐current, localized elevated cytosolic [Ca2+] in the tip, and constant Ca2+‐circulation. For pH, an active H+‐pump and a tightly regulated cytosolic pH at the tip appear important, however not an internal pH‐gradient.
Competition between micro‐organisms and roots of barley and sorghum for iron accumulated in the root apoplasm
Authors: WIRÉN NICOLAUS VON , RÖMHELD VOLKER , SHIOIRI TAKAYUKI , MARSCHNER HORST 
Published: April 2006

SUMMARYGraminaceous plant species respond to iron (Fe)‐deficiency stress by enhancing the release of phytosiderophores from the roots and the uptake of Fe‐phytosiderophores. For studying the mobilization and uptake of apoplasmic root Fe by barley (inherently high phytosiderophore release) and sorghum (inherently low phytosiderophore release) in axenic and nonaxenic (inoculated) nutrient solution, Fe pools in the root apoplasm were loaded during plant preculture with 10‐4 M Fe(III)‐EDTA. After 27 d growth in Fe‐deficient nutrient solution, inoculated barley plants developed moderate Fe‐deficiency chlorosis compared with the less chlorotic axenic plants. In inoculated plants, recovery of phytosiderophores and mobilization of apoplasmic root Fe tended to be slightly lower than in axenic plants, and in both treatments apoplasmic root Fe was completely depleted at harvest. As determined by the nonsoluble Fe fraction (> 0·2 μm) in the nutrient solution and at the rhizoplane, the microbial uptake and immobilization of apoplasmic root Fe was estimated at about 3% of the total amount of apoplasmic root Fe after preculture and at less than 10% of plant Fe uptake.Under axenic conditions, Fe‐deficient sorghum also depleted apoplasmic root Fe and developed moderate Fe‐deficiency chlorosis, although phytosiderophore recovery was 5‐10‐fold lower than in barley. By contrast, in inoculated sorghum plants, phytosiderophore recovery and Fe mobilization were extremely low. At harvest, in inoculated sorghum plants apoplasmic Fe pools were still considerably loaded and plant Fe uptake was c. 60% lower than that of axenic plants, resulting in severe Fe‐deficiency chlorosis. Thus, in Fe‐deficient sorghum plants, the lower rate of phytosiderophore release and its degradation restricted an efficient mobilization of apoplasmic root Fe in the presence of micro‐organisms. In barley, however, the higher rate of phytosiderophore release allowed a complete mobilization of apoplasmic root Fe even in inoculated nutrient solution. Furthermore, the results show that the dominating effect of micro‐organisms in their competition with barley and sorghum for apoplasmic root Fe is the degradation of phytosiderophores rather than the immobilization or uptake of Fe.
The location of sucrose synthase in root nodules of white clover
Authors: GORDON A. J. , THOMAS B.J. , JAMES C. L. 
Published: April 2006

SUMMARYImmunogold labelling was used to identify the location of the sucrose hydrolytic enzyme sucrose synthase in the N2‐fixing root nodules of white clover. This is the major enzyme of sucrose cleavage in clover nodules and might be involved in the modulation of N2 fixation by controlling the rate of utilization of photosynthetic products. Knowledge of the precise cellular location of this enzyme in relation to the point of delivery (the vascular bundles) and the site of utilization of the catabolic product (malate in the bacteroids) might aid our understanding of the metabolic communication between different cell types of the nodule. Gold particle density was greatest in the cytosol of uninfected cells of the central region and in the layer of cortical cells in direct contact with infected cells. By contrast, relative gold particle density was 2–3 fold lower in the cytosol of infected cells. The distribution of sucrose synthase is discussed in relation to sucrose transport, starch metabolism and the provision of carbon and energy for N2 fixation.
Effects of nitrogen supply on the seasonal re‐mobilization of nitrogen in Ulex europaeus
Authors: THORNTON B. , MILLARD P. , TYLER M. R. 
Published: April 2006

SUMMARYNodulated plants of Ulex europaeus L. (gorse) were grown over two seasons in sand. Nutrients were supplied as solutions containing either 0‐25 mol m‐3 NO3‐>, 5·0 mol m‐3 NO3, 0·25 mol m‐3 NH4‐+ or 5·0 mol m‐3 NH4+, as Ca(NO3)2 or (NH4)2SO4. In the first season all nitrogen (N) was enriched with 15N to 5 atom %. In the second season half the plants received the same solution, while the remaining plants received a similar solution in terms of form and amount of nitrogen but at natural abundance. Throughout the second season eight destructive harvests were performed. Plants were separated into roots, nodules, previous season's shoot, new shoot and flowers, and then analysed for total N and 15N content. This allowed estimates to be made of total root N uptake, N2 fixation and the contribution of re‐mobilization to the nitrogen content of new shoot growth in the second season. The main source of N was N2 fixation for plants receiving a low supply of N and root uptake for plants receiving a high supply of N. Plants supplied high NH4+ stored more N over winter than did plants given other treatments. The proportion of over‐wintering stores that were re‐mobilized to support spring shoot growth was unaffected by the capacity of the plants for N2 fixation.