bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of temperature on wood decay and translocation of soil‐derived phosphorus in mycelial cord systems
Authors: WELLS J.M. , BODDY LYNNE
Published: April 2006

Uptake of 32P phosphorus from soil was investigated at 5–25 °C in mycelial cord systems of Phanerochaete velutina (D.C.: Pers.), Hypholoma fasciculare (Huds.: Fr.) Kummer and Phallus impudiciis (L.) Pers. which extended from 2cm3 beech (Fagus sylvatica) inocula, and which had initially developed at either 10 or 25 °C. Uptake of phosphorus from soil was opportunistic, being unaffected by the presence of additional wood resource units in mycelial cord systems. The magnitude of phosphorus uptake was dependent on species, temperature during uptake and the temperature at which cord systems developed. Phosphorus translocation to newly colonized baits, determined non‐destructively, was characterized by an initial rapid flux to a plateau in all three species. Initial rates of phosphorus translocation (up to 18·46 nmol P d‐1) generally increased with temperature whilst total translocation was species and temperature dependent. There was evidence that both P. velutina and H. fasciculare displayed temperature acclimation, since phosphorus uptake and translocation at lower temperatures was greater in cord systems which had developed initially at 10° compared with 25 °C. Mycelial extension and wood decay rates also varied with species, initial development temperature and subsequent incubation temperature, but did not correlate with the temperature profiles of phosphorus uptake and translocation. Results are discussed in relation to nutrient acquisition, conservation and cycling in basidiomycete mycelial cord systems.
A light‐ and electron‐microscopic study on a vesicular–arbuscular host‐fungus interaction in gametophytes and young sporophytes of the Gleicheniaceae (Filicales).
Authors: SCHMID ELFI , OBERWINKLER FRANZ
Published: April 2006

Gametophytes and primary roots of young sporophytes of the Gleicheniaceae were studied by means of light‐ and electron microscopy. An aseptate fungus invaded the gametophyte tissue through the rhizoids. The fungus spread within the thickened midrib forming intracellular hyphal coils. The latter gave rise regularly to arbuscules which were cytoplasmic in the young part of the midrib. In the older midrib, arbuscules degenerated and vesicles occurred. With arbuscular development, host cytoplasm and cell organelles increased and starch disappeared from plastids. The fungus formed globose spores inside the rhizoids. The gametophyte fungus did not transverse the gametophyte‐ sporophyte junction. Primary roots shorter than 2 mm were not infected. Primary roots longer than 2 mm showed vesicular–arbuscular mycorrhiza with a completely intracellular development of the fungus.
Clover as an indicator plant for phytotoxic ozone concentrations: visible injury in relation to species, leaf age and exposure dynamics
Authors: KARLSSON G. PIHL , SELLDÉN G. , SKÄRBY L. , PLEIJEL H.
Published: April 2006

Visible ozone injury on leaves of three clover species was investigated in relation to species, leaf age and exposure dynamics. It was shown that ozone episodes in south‐west Sweden cause visible injury to subterranean clover (Trifolium subterraneum L.), white clover (Trifolium repens L.) and red clover (Trifolium pratense L.). Trifolium subterranean was most sensitive to ozone, whilst T. pratense was least sensitive. Application of the anti‐ozonant, ethylenediurea (EDU), reduced the extent of visible ozone injury, but did not give complete protection with the concentrations used. Similarly, filtration of the air reduced the extent of visible injury in T. subterraneum enclosed in open‐top chambers. EDU‐treated plants of T. subterranean accumulated more biomass than the non‐EDU treated plants after a period with rather high ozone concentrations, while the opposite occurred for T. pratense. Experiments with T. subterraneum in open‐top chambers also showed that older leaves were more sensitive to ozone than younger leaves and that a shorter period with higher ozone concentrations produced more ozone injury than a longer period with lower ozone concentrations, although the two periods had the same number of ppb‐hours.
Effects of disease in wild plant populations and the evolution of pathogen aggressiveness
Authors: JAROSZ ANDREW M. , DAVELOS ANITA L.
Published: April 2006

Fungal 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

Nitrogen 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

A 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

Electrical 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

The 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

A 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

Movement 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

Detailed 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

Hartel'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

The 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

In 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

Graminaceous 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

Immunogold 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

Nodulated 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.
Nitrogen, phosphorus and potassium uptake and demand in Agrostis capillaris: the influence of elevated CO2 and nutrient supply
Authors: NEWBERY R. M. , WOLFENDEN J. , MANSFIELD T. A. , HARRISON A. F.
Published: April 2006

Responses to elevated CO2 have been studied using Agrostis capillaris L., an upland grass which is abundant on nutrient‐poor soils. Plants were grown in sand culture with a wide range of nitrogen, phosphorus and potassium concentrations, and the impact of CO2 on the demand for nutrients was determined using isotopic root bioassays. Plants grown with the smallest concentrations of N and P showed typical foliar symptoms associated with deficiency of these elements. However, even when supplies of N and P were limiting to growth, additional CO2 (250 ppm above ambient) influenced neither total N nor total P in above‐ground tissues, nor nutrient demands as indicated by the bioassay. The estimates of the demand of the plants for K from the 86Rb bioassay indicated an appreciable increase when plants were raised in elevated CO2. For plants of the same size with the same nutrient supply, those grown in elevated CO2 consistently displayed an increased internal demand for K. Uptake of K was not however, enhanced by elevated CO2 even in non‐limiting conditions and it might therefore be limited by a factor other than K supply. The overall conclusion from the experiments is that when A. capillaris is grown in elevated CO2, uptake of N, P and K fails to increase proportionally with dry mass. This was true even when nutrient supplies were adequate, and it appears that nutrient‐use‐efficiency might increase to enable the plants to maintain growth in elevated CO2.
Field study of leaf photosynthetic performance by a Mediterranean deciduous oak tree (Quercus pubescens) during a severe summer drought
Authors: And C. DAMESIN , RAMBAL S.
Published: April 2006

Quercus pubescensWilld. is a winter deciduous oak species which co‐occurs in the Mediterranean area with an evergreen oak,Q. ilex.As the knowledge ofQ. pubescensassimilation patterns is poorly documented, we monitored leaf physiological parameters throughout a growing season. In summer, drought was particularly severe, and some trees experienced pre‐dawn water potentials (Ψpd) as low as – 4·5 MPa. Diurnal courses of net photosynthesis, stomatal conductance and I photochemical efficiency of photosystem II (PS II) were recorded on four trees in the field. Maximum assimilation rates (10–16·5 μmol m−2s−1, depending on sampled trees) occurred in spring. Leaf carbon gain recovered in autumn even after water potential fell to – 3·4 MPa. During progressive drought, Ψpddecreased substantially, leaf gas exchange was reduced and showed an important diurnal depression. At – 2 MPa (Ψpd), net photosynthesis and stomatal conductance were still about 5 μmol m−2s−1and 50 mmol m−2s−1, respectively. Pre‐dawn maximal PS II photochemical efficiency was stable to – 4 MPa. The diurnal decrease in photochemical efficiency of PS II (Fv/Fm), measured after 30 min of dark adaptation, was enhanced during drought but maximal values always recovered at sunset, i.e. leaves only experienced short‐term reversible PS II inhibition induced by high light and temperature. In conclusion,Q. pubescensdisplays a strategy of tolerance to drought and an efficient protection against high irradiance.
Modelling pea (Pisum sativum) root growth in drying soil. A comparison between observations and model predictions
Authors: TSEGAYE TEZERA , MULLINS C. E. , DIGGLE A. J.
Published: April 2006

Peas were grown in the glasshouse for 29 d in duplicate 1 m tall containers packed with soil at field capacity (a matric potential of –0·005 MPa) to a bulk density of 1·30 Mg m−3 and with an initial penetration resistance (PR) of 0·35 MPa. Counts of new root contacts on the sides of the containers and matric potential (Ψm) measurements at 0·1 m depth increments were made every two days. Although the plants were not watered, matric potential was never less than –0·041 MPa and was unlikely to have directly limited root growth, but it was used as a predictor of PR and hence of the effect of PR on root growth rate. The effect of PR on root growth was predicted using experimentally determined relationships between root growth rate and PR, and PR and Ψm. These results were used with the ROOTMAP root growth model to give two different model scenarios: (1) variable resistance (VR), allowing mechanical impedance to vary with time and depth in line with the observed values of Ψm and (2) constant resistance (CR), maintaining mechanical impedance at its value at the start of the experiment. CR predictions gave a gross overestimate of the rate at which new root contacts were made on the container walls, whereas VR predictions agreed with experimental observations to within the limits of accuracy of the model and the observations. The comparison between CR and VR predictions gives a clear demonstration of bow the increase in soil strength caused by roots drying the profile can result in a reduction in the size and extent of the whole root system.
Responses of pine needle endophytes to air pollution
Authors: HELANDER MARJO L.
Published: April 2006

The effects of heavy metals and sulphuric acid on pine needle endophytes were studied using gradient analyses, an experimental field study and an in vitro laboratory experiment. Gradient analyses were carried out near factory complexes at Harjavalta (southern Finland) and Monchegorsk (Kola peninsula, Russia); both factories emit heavy metals and sulphur. The experimental field plots had received copper (Cu) and nickel (Ni) treatment, sulphuric acid treatment, or a combination of the two, for 3 yr before sampling. Endophyute strains isolated 1 and 8 km from the factory were studied for their mental tolerance in the laboratory. The total number of needles infected with endophytes and also the number of needles infected with a specific endophyte, Cenangium ferrucinosum Fr.:Fr., were significantly lower near factories than at the control area. The frequency of the endophyte Hormonema sp., on the other hand, was not correlated with distance from the factory. In the experimental field study, the total number of endophyte‐infected needles was not affected by the treatments. The number of needles infected with Hormonema sp., however, was significantly lower in the Cu and Ni treated trees than in irrigated controls. Hormonema sp., strains isolated near the Harjavalta factory were more tolerant of Cu and Ni in vitro than were those isolated 8 km from the factory.
Exposure of spring wheat (Triticum aestivum) to ozone in open‐top chambers. Effects on acyl lipid composition and chlorophyll content of flag leaves
Authors: SANDELIUS ANNA STINA , NÄSLUND KRISTINA , CARLSSON ANDERS S. , PLEIJEL HÅKAN , SELLDÉN GUN
Published: April 2006

Spring wheat (Triticum aestivumL. cv. Drabant) was exposed to different concentrations of ozone in open‐top chambers in a field of commercially grown wheat. The following treatments were used: charcoal‐filtered air (CF), non‐filtered air (NF) and non‐filtered air supplemented with 25 nl 1−1 ozone (NF+) and 35 nl 1−1 ozone (NF ++) for 7 h d−1. Flag leaves were analysed for chlorophyll content, total fatty acid composition and fatty acid compositions and contents of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The chlorophyll content decreased significantly with time and ozone concentration. After 4 wk of exposure, the content of MGDG was significantly lower in flag leaves from the N F ++ treatments than in those from the other treatments. The contents of DGDG and PC also decreased while that of PE increased, although these changes were not statistically significant. In the total lipid extract the proportion of 18:3 decreased with time and ozone concentration. Similar changes occurred in MGDG 18:3 at a later stage. Using the concept of accumulated exposure over threshold (AOT), it was evident that the parameters studied differed in ozone sensitivity. After 4 wk of exposure, the best linear dose‐response relationships between accumulated exposure and chlorophyll as well as MGDG contents were obtained with a threshold ozone concentration of 30 nl l−1. For total lipid 18:3 and MGDG 18:3 the corresponding thresholds were 40 and 50 nl 1−1, respectively. Furthermore, the sensitivity to ozone, expressed as loss of chlorophyll, increased with increasing flag leaf age. In leaves exposed for 7, 13 and 20 d, the best linear fits were obtained with AOT50, AOT40 and AOT30, respectively. In conclusion, ozone sensitivity increased with flag leaf age and different membrane constituents were differently sensitive to ozone. The results support previous suggestions that ozone causes premature senescence in wheat flag leaves.
A process‐oriented explanation of the nonlinear relationship between grain yield of wheat and ozone exposure
Authors: PLEIJEL HÅKAN , SKÄRBY LENA , WALLIN GÖRAN , SELLDÉN GUN
Published: April 2006

A model for the impact of ozone on grain yield in spring wheat (Triticum aestivum L.) was constructed. The mode was based on the observations in the literature as well as in the present experiment, that the productivity of the above‐ground biomass and the carbon partitioning of the above‐ground biomass do not respond to ozone above the same threshold concentrations. The model was applied to a data set in which spring wheat was exposed to different ozone concentrations in open‐top chambers. It was concluded that the nonlinearity of a simple dose‐response curve for grain yield can be explained in terms of the product of two linear responses: (1) the response of total above‐ground biomass to an ozone dose above 10 nl 1−1, and (2) the response of the harvest index to an ozone dose above 40 nl 1−1 The nitrogen content of the grain increased linearly with the dose above 40 nl 1−1.It is hypothesized that the effect of comparatively small ozone concentrations on total above‐ground biomass is caused by a reduction of leaf duration by ozone, and that the effect on carbon partitioning is caused by ozone affecting the sink capacity or activity of the growing grain. The maximum coefficients of determination (r2) for the linear regression between grain yield and accumulated ozone dose above thresholds in the range of 0–70 nl 1−1, were never as great as those for total above‐ground biomass and harvest index. Nevertheless, statistically significant linear regressions were obtained for the thresholds 20, 30 and 40 nl 1−1, the highest correlation being with 30 nl 1−1 Thus, it seems acceptable to use linear regressions between grain yield and the accumulated dose, although these do not take into direct account the complexity of the effects of ozone on wheat.
Determinations of dye diffusivities in the cell‐wall apoplast of roots by a rapid method
Authors: BAYLISS C. , VAN DER WEELE C. , CANNY M. J.
Published: April 2006

summary

A method is described of measuring dye diffusivity through the cell‐wall apoplast of roots, using sections of fresh material cut by hand under paraffin oil. Root pieces of Vicia faba and Glycine max were immersed in a solution of sulphorhodamine G for short periods, and the advance of the dye through the cell‐wall apoplast was measured, either in a number of sections cut after various periods of diffusion, or by photographing the same section at intervals while diffusion into it from the surface was observed under the microscope. Fick's second law was used to estimate the diffusivity. Diffusivities, expressed relative to the diffusivity in water (Daq) were in the range Daq/16 to Daq/55 for Vicia roots. The values for Glycine roots showed a wide scatter, with a modal value of Daq/1700. Comparison of this rapid method with the much more laborious stabilization of the dye by freeze‐substitution confirmed the values of measured diffusivities in Vicia.
Morphological and biochemical characterization of spikelet development in naked oats (Avena sativa)
Authors: OUGHAM HELEN J. , LATIPOVA GALINA , VALENTINE JOHN
Published: April 2006

summary

The dominant gene N‐1 in cultivated oats gives rise to a phenotype characterized by a thin papery lemma from which the grain readily threshes free, a multiflorous habit, and rachillas that are elongated in comparison to those of husked oats. This study was undertaken in order to identify the stages at which morphological and biochemical development of naked and husked oats begin to diverge, and to look for correlated differences in gene products (mRNAs and proteins). Spikelet morphology in naked and husked oats was shown to diverge early in panicle development: the first visible difference was premature cessation of growth of the third and subsequent florets in husked oats. Lignin deposition in the lemma occurred later and followed a similar time‐course in both genotypes, though in naked oats it was restricted to the vascular bundles. Mature lemmas of the naked genotype closely resembled glumes in appearance and in lignification pattern. Genotypic differences in extractable polypeptide complements were apparent only late in development, coinciding with the onset of lignification, and were not associated with comparable differences in translatable mRNA profiles. The normal (n‐1) allele at the naked locus is likely to encode a transcription factor with properties similar to those of previously‐characterized homeotic gene products in plants.
Lead phytoextraction: species variation in lead uptake and translocation
Authors: HUANG J. W. , CUNNINGHAM S. D.
Published: April 2006

summary

Lead transport has been characterized in corn (Zea mays L. cv. Fiesta) and ragweed (Ambrosia artemisiifolia L.), and the Pb phytoextraction efficiency of these species has been compared with that of Tritiaim aestivum, Thlaspi rotundifolium, Thlaspi caerulescens and Brassica juncea, using both nutrient solutions and Pb‐contaminated soils. Our results demonstrated that plant species differ significantly in Pb uptake and translocation. In short term (60 min) experiments, Pb uptake by ragweed roots was threefold higher than that by corn roots. After 2 wk of Pb (100/yM) exposure in hydroponics, root‐Pb concentration was 24000 mg kg−1 for ragweed and 4900 mg kg−1 for corn. In contrast to root‐Pb concentration, shoot‐Pb concentration was significantly higher in corn (560 mg kg−1) than in ragweed (30 mg kg‐1). At an external Pb concentration of 20/IM, corn concentrated Pb in shoots by 90‐fold, and ragweed concentrated Pb in shoots by 20‐fold over the solution Pb concentration. Of the 11 species/cultivars tested using both nutrient solutions and Pb‐contaminated soils, corn accumulated the highest shoot‐Pb concentration. Using this corn cultivar, we investigated the role of synthetic chelates in Pb phytoextraction. Addition of HEDTA (2.0 g kg−1 soil) to a Pb‐contaminated soil (total soil Pb 2500 mg kg−1) resulted in a surge of Pb accumulation in corn. The shoot Pb‐concentration was increased from 40 mg kg−1 for the control (‐HEDTA) to 10600 mg kg−1 for the HEDTA‐treated soil. To our knowledge, this is the highest shoot Pb concentration reported in the literature for plants grown on Pb‐contaminated soils. Our results suggest that in combination with sou amendment, some agronomic crops, such as corn, might be used for the clean‐up of Pb‐contaminated soil.
Decomposition, nitrogen and phosphorus mineralization from beech leaf litter colonized by ectomycorrhizal or litter‐decomposing basidiomycetes
Authors: COLPAERT JAN V. , VAN TICHELEN KATIA K.
Published: April 2006

summary

The decomposition and the nitrogen and phosphorus mineralization of fresh beech (Fagus sylvatica L.) leaf litter are described. Leaves were buried for up to 6 months in plant containers in which Scots pine (Pinus sylvestris L.) seedlings were cultivated at a low rate of nutrient addition. The saprotrophic abilities of three ectomycorrhizal fungi, Thelephora terrestris Ehrh.: Fr., Suillus bovinus (L.: Fr.) O. Kuntze and Paxillus involutes (Batsch: Fr) Fr., were compared with the degradation caused by the litter‐decomposing basidiomycete, Lepista nuda (Bull.: Fr.) Cooke. Uninoculated leaves were included as controls. The investigation was performed at two different pH values since substrate pH is supposed to have an effect on the activities of extracellular enzymes of ectomycorrhizal fungi. The enzyme expression might also be largely influenced by the substrate they colonised. The mycorrhizal fungi caused only a low decomposition rate of the litter compared with that of L. nuda, and nitrogen was released only by L. nuda. Leaves colonized by mycorrhizal fungi showed no net release of nitrogen; on the contrary, a small accumulation of N in the litter was observed. It therefore seems likely that the ectomycorrhizal fungi studied do not have the ability to decompose efficiently the lignocellulose matrix of the relatively recalcitrant beech leaf litter. The degradation of this matrix seems to be essential for the fungi to gain access to the leaf nitrogen pool of fresh beech litter. A direct release of nitrogen from organic compounds by ectomycorrhizal fungi seems therefore to be confined to the older litter layers. The beech leaf litter contained an important fraction of easily mineralizable phosphorus. P was not a growth limiting factor m the cultivation system, and could therefore accumulate in the leaf litter colonized by the ectomycorrhizal mycelium.
Tissue localization of u.v.‐B‐screening pigments and of chalcone synthase mRNA in needles of Scots pine seedlings
Authors: SCHNITZLER JÖRG‐PETER , JUNGBLUT TIM P. , HELLER WERNER , KÖFFERLEIN MATTHIAS , HUTZLER PETER , HEINZMANN ULRICH , SCHMELZER ELMON , ERNST DIETER , LANGEBARTELS CHRISTIAN , SANDERMANN HEINRICH
Published: April 2006

summary

Epidermal tissue was isolated from Scots pine (Pinus sylvestris L.) needles by enzymatic digestion in order to study tissue distribution of u‐V.‐B‐screening pigments. Up to 90% of the needle content of a group of diacylated flavonol glycosides that were structurally closely related was found in the epidermal layer. Among these metabolites, 3″,6″‐di‐paia‐coumaroyl‐isoquertitrin and 3″,6″‐di‐para‐di‐coumaroyal‐astragalin were the main u.v.‐B‐induced compounds in cotyledons and primary needles, respectively. However, catechin and astragalin (kaempferol 3‐glucoside), two non‐acvlated flavonoid metabolites, were only observed in total needle extracts, and at levels independent of u.v.‐B treatment. According to this metabolite distribution, the mRNA of chalcone synthase, the key enzyme to flavonoid, was found in epidermal and mesophyll as well as vascular tissues. The major alkali‐extractable wall‐bound phenolic metabolites, astragalin, 4‐coumaric acid, and ferulic acid, a minor component of the cell wall, were also found exclusively in the epidermal layer. These compounds were not stimulated by u.v.‐B irradiation within the experimental period. Staining of needle cross sections and epidermal layer preparations with Naturstoffreagenz A confirmed the specific localization of wall‐bound astragalin in the outer wall of the epidermal layer. Model calculations of u.v.‐B absorptions at 300 nm of soluble and cell‐wall‐bound metabolites of the epidermal layer revealed an almost complete shielding of the mesophyll tissue From u.v.‐B radiation.