bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential heat sensitivity amongst four populations of the lichen Ramalina menziesii Tayl.
Authors: Larson D. W.
Published: April 2006

An investigation was made of the degree of physiological differentiation in response to high temperatures, in the lichen Ramalina menziesii Tayl. The range of this species extends from cool coastal rainforest in British Columbia, Canada to hot and dry coastal desert in Baja California del Sur, Mexico. Thalli were collected from four extreme positions within the range and exposed to temperature pretreatments ranging from 20 to 70 °C in 10 °C increments for 7‐5 h. Rates of net photosynthesis, dark respiration and calculated gross photosynthesis were then determined. There was physiological differentiation among the four populations at a narrow range of pretreatment temperatures so that Thalli derived from the site with the least heat stress show the least resistance, while Thalli derived from the site with the most heat stress show the most heat resistance. This suggests that physiological as well as morphological plasticity is important to the ecology of this lichen. It also suggests that high temperatures alone do not act to restrict the distribution of this species.
Anatomy of a vesicular—arbuscular endomycorrhizal symbiosis between sugar maple (Acer saccharum Marsh) and Glomus etunicatum Becker & Gerdemann
Authors: YAWNEY W. J. , SCHULTZ R. C.
Published: April 2006

Summary

Microscopic analysis of infection development by Glomus in sugar maple roots revealed changes in the cortical cells similar to those reported by other workers using either herbaceous or woody plant hosts. Few cortical cells contained exclusively terminate hyphal structures. Instead, large intracellular hyphae entered and exited cortical cells while arbuscules formed from initiation points at various places on the intracellular hyphae. Intercellular hyphae were rare and vesicles were not observed. The beaded root morphology observed did not seem to influence the infection process. Beaded roots are formed from repeated constrictions in feeder roots due to major reductions in cell size. The relationship between the constrictions and moisture stress is discussed. The living arbuscule seemed to be the site of transfer between the host and endophyte, implying that the process is an active one.
The role of the external mycelial network in the effect of soil disturbance upon vesicular—arbuscular mycorrhizal colonization of maize
Authors: EVANS D. G. , MILLER M. H.
Published: April 2006

Summary

This study examined the mechanism by which vesicular‐arbuscular (VA) mycorrhizal colonization of young maize (Zea maysL.) plants is inhibited by soil disturbance. Attention focussed upon the role of the external mycelial network.

Plastic cylinders were divided into a central and two outer compartments by a fine nylon mesh screen which was impervious to roots but not to mycorrhizal hyphae. Soil was packed into each compartment and maize plants grown in the outer compartments over a series of 3‐week cycles, leaving root‐free central sections. Prior to a final growth cycle, the root‐free soil in the central compartment was either disturbed and repacked or left undisturbed. In a third treatment the hyphal connections between the outer and central sections were severed, while leaving the soil in all sections undisturbed. Plants were then grown in the central compartments.

Mycorrhizal colonization and shoot P and Zn concentrations of plants grown in the root‐free zones were substantially reduced by disturbance of the soil. The reduction in colonization was similar to that found in control pots in which the root system and mycelial network were disturbed. This suggested that destruction of the hyphal network is an important component in the disturbance phenomenon. Removal of hyphal connections with roots in the outer compartments had no effect on colonization or nutrient absorption. Isolation of the mycelial network from the root system from which it had originated did not then seem to affect its infectivity.

The mycelial network appears to be an important component of the inoculum potential of an undisturbed soil and it is likely that its destruction is directly responsible for much of the effect of soil disturbance upon mycorrhizal colonization. Evidence is presented indicating that the undisrupted mycelial network may also increase the nutrient absorption capacity independent of the degree of colonization.
First syntheses of ectomycorrhizas between Afzelia africana Sm. (Caesalpinioideae) and native fungi from West Africa
Authors: BA A. M. , THOEN D.
Published: April 2006

Summary

Afzelia‐associated fungi in Senegal were isolated from sporocarps, sclerotia and ectomycorrhizas. The choice of sterilizing agent was critical for the success of isolation. Osmic acid was more efficient than mercuric chloride, hydrogen peroxide and calcium hypochlorite. Isolates were tested for their ability to form mycorrhizas in vitro and their mycelia in pure culture were described. Sclerotia linked to mycorrhizas of Scleraderma verrucosum Pers. were also isolated and their infectivity checked. Among isolates from sporocarps, only Scleroderma dictvosparum Fat. and S. verrucosum Pers. formed ectomycorrhizas with Afzelia africana Sm. Two native Amanita spp. and two introduced isolates belonging to the genus Pisolithus did not form typical ectomycorrhizas although a normal mantle was observed.
Light‐enhanced convective throughflow increases oxygenation in rhizomes and rhizosphere of Phragmites australis (Cav.) Trin. ex Steud.
Authors: ARMSTRONG J. , ARMSTRONG W.
Published: April 2006

Summary

The convective throughflow of gases found recently in Phragmites australis increased with increasing fluxes of photosynthetically active radiation. Despite this, the oxygen in the venting gases remained lower than in air and the convection is thought to depend mainly on a humidity‐induced diffusion of atmospheric gases across the leaf sheaths. When convection was prevented, and aeration was dependent entirely upon diffusion, no photosynthetic enhancement of rhizome and root aeration could be detected.

In terms of oxygen transport, rapid rates of convection were much more effective than diffusion and substantially enhanced the entry of oxygen into the rhizome system. This resulted in large increases in the efflux of oxygen into the rhizospheres of basal laterals and apical and sub‐apical regions of the adventitious roots. This effect was attributed to a greater diffusion of oxygen from rhizome to root. Substantial diurnal fluctuations in rhizome oxygen regimes and in root oxygen efflux occurred.

It is estimated that because of convection and diffusion, up to 0.31 kg of oxygen d−1 m−1 may enter the rhizome system of vigorous stands of Phragmites during summer months. By comparison, diffusion alone could be expected to supply less than 0.01 kg d−1. Scanning electron micrographs of root‐shoot junctions showed that the resistance to gaseous diffusion from rhizome to roots must be especially small in Phragmites.
Growth of Pyrola rotundifolia ssp. maritima in relation to shade
Authors: HUNT RODERICK , HOPE‐SIMPSON J. F.
Published: April 2006

Summary

The maritime race of the larger wintergreen [Pyrola rotundifolia L. ssp. maritima (Kenyon) E. F. Warb.] was investigated in relation to its light environment at Braunton Burrows in south‐west England.

Measurements made at the site of its greatest abundance indicated that, in July, Pyrola commonly experiences an irradiance which is below 10% of full daylight with some habitats providing less than 1%. The species also occurs in situations receiving up to 100% daylight; at or towards this extreme the foliage is yellowish‐green instead of deep green, giving an impression of reduced luxuriance.

The mean specific leaf area of plants growing in the field was found to be inversely related to mean percentage irradiance received at each site. However, the slope of this trend was slight.

Detached, rooted rosettes were removed from the field and grown for 85 days in a glasshouse under treatments which provided 100, 20.2 and 6.1% daylight. The plants in all treatments appeared normal but growth was slow. Yields and relative growth rates were significantly reduced by shading (P 0–05). The depressing effect of shading on growth rate was very slightly less than on unit leaf rate, the difference being due to slight increases in leaf area ratio. This, in turn, was tracted entirely to small increases in specific leaf area. Leaf weight ratio was not affected significantly, nor were substantial effects recorded in root/shoot ratio or in fresh weight/dry weight ratio.

We conclude that the vegetative growth of Pyrola has a low capacity for adjustment to both natural and experimental shading; its growth rate in the field will tend to be lower under a dense leafy canopy than in less shaded habitats. The inherently low growth rate might, however, be an advantageous feature under shade conditions. The evident success of the species in shaded situations is certainly due to factors other than a simple shade requirement for vegetative growth.
Crystal occurrence and wax disruption on leaf surfaces of cabbage treated with simulated acid rain
Authors: ADAMS CINDY M. , CAPORN SIMON J. M. , HUTCHINSON THOMAS C.
Published: April 2006

Summary

Epicuticular waxes on leaves of Brassica oleracea L. (cabbage) were studied using scanning electron microscopy after a single treatment with simulated rain of pH 5.6, 3.0 or 2.5 which was either sprayed on to plants in an exposure chamber or applied as droplets with a micropipette. Treatments with acidified rain caused serious structural degradation of the wax crystals. The alteration of crystalline wax structures was similar for leaves treated with nitric acid solutions, but less severe, than for leaves treated with sulphuric acid solutions. With both H2SO4, and HNOa‐derived rain solutions numerous gypsum (CaSO4) crystals were found in and near lesions on the leaves treated with rain of pH 3.0 and 2.5. The crystals probably resulted from damage of cuticular membranes by acidic rain which significantly altered their permeability to ions in the area of lesions. Crystalline leaf waxes may be an important target for acidic pollutants, and the physiological consequences of their degradation are discussed.
The stimulation of CAM activity in Mesembryanthemum crystallinum in nitrate and phosphate‐deficient conditions
Authors: PAUL M. J. , COCKBURN W.
Published: April 2006

Plants of Mesembryanthemum crystallinum L. were grown from seed in phosphate‐sufficient and phosphate‐deficient conditions. Separate plants were subjected to nitrate deficiency by removing nitrate from the rooting medium of previously nitrate‐sufficient plants. Subsequently, they were also irrigated with 400 mM NaCl to induce CAM. Plants of M. crystallinum with induced CAM that had been grown in complete nutrient medium were deinduced by rehydration.

Nitrate and phosphate deficiencies caused enhanced CAM activity prior to salt treatments. After salinisation, phosphate deficiency also caused higher background levels of malate. Prolonged nitrate deficiency reduced CAM activity.

Endogenous P1 levels in phosphate‐sufficient plants correlated with CAM activity. However in phosphate‐deficient plants CAM occurred without a significant rise in P1 content. Levels of endogenous P1 appeared more related to nitrate deficiency than to CAM or salt treatment. Nitrate and phosphate deficiencies and salt treatment could all cause a nitrate deficiency within the leaf, causing high endogenous P1 when available in the rooting medium. It is speculated that a change in nitrogen status could play a role in the initiation of CAM induction in M. crystallinum. A further possibility is that CAM could be induced by reduced water potential due to dehydration and increased ion content in saline conditions, and by an inhibition of growth and concomitant accumulation of solutes in phosphate‐ and nitrate‐deficient conditions.
Changes in intracellular amino acids and glutamine : glutamate during N‐deprivation and feeding in Candida nitratophila
Authors: FLYNN K. J. , HIPKIN C. R.
Published: April 2006

In the yeast, Candida nitratophila Shifrine et Phaff, the intracellular concentrations of α‐amino acids decreased rapidly during N‐deprivation, with the ratio of glutamine: glutamate (Gln: Glu) falling from 07 in NH4+‐grown cells, or 0.5 in NO3−‐grown cells, to 0.1 after 1 h. Addition of NH4+ to N‐deprived cultures resulted in rapid increases in glutamate, glutamine and alanine with Gln: Glu exceeding 1.5 within 30 min. Recovery of other amino acids, such as arginine, was much slower. Addition of NO3, resulted in a less rapid increase in the concentration of some intracellular amino acids, including glutamate and glutamine, while levels of arginine continued to fall for 30 min after addition of this N‐source. Gln: Glu was slow to rise in NO3− pulsed cells. Addition of NH4+ to cells growing on NO3− produced little change over the following 2 h other than decreases in arginine and histidine. Carbon deprivation resulted in a rapid decrease in levels of glutamate, glutamine and alanine, but not of aspartate (which this yeast is unable to use as a sole C‐source for growth) or arginine. Gln: Glu increased during C‐deprivation but fell within 10 min to normal levels on addition of glucose. It is concluded that, in C. nitratophila, Gln:Glu values correlate well with C‐N status.
The influence of ozone and acid mist on the amount and wettability of the surface waxes in Norway spruce [Picea abies (L.) Karst.]
Authors: BARNES J. D. , BROWN K. A.
Published: April 2006

Three‐year old Norway spruce [Picea abies (L.) Karst.] trees from two clones (4076 and 4102) of a medium altitude southern German provenance were transplanted in May 1986 into an acid brown earth soil. During the summers of 1987 and 1988 the trees were exposed in large‐scale fumigation chambers (solardomes) to ozone at 100 or 20 nl 1−1 (control). Acid (pH 3.6) or control mist (pH 5.5) was applied daily to trees. The wettability of current and 1‐year‐old needles was assessed in November 1988 by measuring the contact angle of water droplets placed on needles, and the amount of surface wax was determined. The contact angle of water droplets on current and 1‐year‐old needles was significantly reduced by 100 nl 1−1 PPB ozone and/or acid mist, indicating that the wettability had increased, but the combined effect of ozone and acid mist was no more than additive. Exposure to the pollutants resulted in a slight decrease in the quantity of surface wax, but the effect was not significant. Ozone and acid mist treatment also increased the projected area of needles relative to their dry weight. The possible involvement of such effects in forest decline are discussed.
Growth responses of barley exposed to SO2
Authors: MURRAY FRANK , WILSON SUSAN
Published: April 2006

Barley (Hordeum vulgare ev. Schooner) plants were exposed to 4, 42, 121, 256 or 517 nl 1−l SO2 to investigate the relationship between the exposure concentration of SO2 and growth. The plants were exposed from 14 days old, in open‐top chambers for 4 h day−1 (10.00‐14.00 h) for 79 days. The concentration‐response curves established illustrated a small growth stimulation (approx. 10%) at 42 nl 1−1 and a growth inhibition at 121 nl 11− or greater. The growth reduction was generally proportional to the exposure concentration at concentrations above 42 nl 1−1 Sulphur concentration in the shoot increased linearly with ambient SO2 concentration.
Evidence for early changes in membrane structure during post‐harvest development of cut carnation (Dianthus caryophyllus L.) flowers
Authors: PALIYATH G. , THOMPSON J. E.
Published: April 2006

Freeze‐fracture electron microscopy and X‐ray diffraction have indicated that there are marked alterations in membrane structure prior to the initiation of increased ethylene production and petal inrolling during post‐harvest development of cut carnation flowers. In replicas of petals from partially open flowers (stage 1 of post harvest development), an even distribution of intramembranous particles, which is characteristic of normal membranes, was evident on the fracture plane of the plasma membrane. By contrast, endoplasmic reticulum membranes had begun to develop intramembranous particle‐free areas indicative of gel phase lipid domains. By stage 2 of development, when the flowers were fully open, large areas devoid of intramembranous particles were apparent on the plasma membrane as well. The presence of gel phase lipid was confirmed by wide‐angle X‐ray diffraction of isolated microsomes. Imaginations reflecting microvesiculation were also discernible in the fracture planes of plasma membrane at stage 2 of development and vesicles lying adjacent to the cell surface were evident in the cytoplasm. These observations collectively indicate that there are deteriorative alterations in membrane structure during the very early stages of post‐harvest development in cut carnation flowers. They also provide an explanation for the previous finding that carnation petals become leaky well before morphological symptoms of senescence such as petal inrolling are apparent.
The fate of soil‐derived phosphorus in mycelial cord systems of Phanerochaete velutina and Phallus impudicus
Authors: WELLS J. M. , HUGHES C. , BODDY LYNNE
Published: April 2006

This study demonstrated the direct uptake of [32P]phosphorus from soil by ‘foraging’ cord systems of Phanerochaete velutina (DC: Pers.) Parmasto and Phallus impudicus (L.) Pers., grown from 4 cm3beech (Fagus sylvatica L.) wood inocula. Total uptake was independent of, but ‘allocation’ within cord systems dependent on, species, the state of decay of wood inocula, and phosphorus availability in different parts of cord systems. Cords were shown to be functional pathways for translocation of 32P between distant resource units and more than 90 % of accumulated phosphorus was translocated to the inocula or to new resource units. Allocation of opportunistically‐scavenged phosphorus was in preferential order of the potential of new resource units as carbon sources and in proportion to the mass of like resource units. Non‐destructive 32P determination, using a scintillation probe, showed that significant differences (P 0.05) in allocation to combinations of new resource units could be detected within 12 d and corresponded with the results of destructive total 32P determination after nine weeks. The results are discussed in terms of the role of saprotrophic cord‐forming basidiomycetes in nutrient cycling and the efficiency of nutrient allocation within their cord systems.
Iǹtraspecific variation in two species of Suillus from Scots pine (Pinus sylvestris L.) forests based on somatic incompatibility and isozyme analyses
Authors: SEN R.
Published: April 2006

Isolates of Suillus variegatus (Swartz ex Fr.) O. Kuntze and Suillus bovinus (Fr.) O. Kuntze cultured from basidiocarps collected in different geographically located Scots pine (Pinus sylvestris L.) forests were subjected to an analysis of axenic growth rates, somatic incompatibility and electrophoretic isozyme expression. Intraspecific variation in the radial growth rates and at certain putative enzyme loci was detected in these fungal populations which, after tests for somatic incompatibility, were identified as being composed mainly of different clones. Following a numerical analysis of the isozyme data of seven enzyme systems, considerable interspecific dissimilarity (11% similarity) and intraspecific similarity (> 65% similarity) were detected in these fungi. Isozymes of esterase, peptidase and acid phosphatase were conserved within species but differed between these species enabling their unambiguous identification. Isolates of S. variegatus were found in two main clusters that represented the two forest locations from which they were collected. A single putative locus of glutamate oxaloacetate transaminase was found to display isozyroe polymorphism directly related to the forest location of the isolates. No habitat‐related isozyme activities could be detected in the isolates of 5. bovinus which, unlike those of S. variegatus, exhibited isozyme expression that was strongly dependent upon the medium. Isolates of S. variegatus and S. botinus identified as originating from the same vegetative clone by somatic incompatibility testing were found to exhibit 100 and 93‐97% similarity in their respective isozyme activities. These studies indicate that isozyme analyses in conjunction with somatic incompatibility testing will provide powerful tools for the genetic analysis of ectomycorrhizal communities.
Iσozymic identification of individual ectornycorrhizas synthesized between Scots pine (Pinus sylvestris L.) and isolates of two species of Suillus
Authors: SEN R.
Published: April 2006

Morphologically similar ectornycorrhizas between Scots pine (Pinus sylvestris L.) seedlings and different geographic isolates of Suillus variegatus (Fr.) O. Kuntze and Suillus bovinus (Fr.) O. Kuntze were synthesized under semi‐aseptic conditions in a sand and peat growth mixture containing ureaformaldehyde as the organic nitrogen source. Fourteen weeks after inoculation significant increases in shoot height were recorded in most of the infected seedlings and in two inoculated treatments where no mycorrhizal infection was detected. Based on the assumption that 50% of the dry mass of these ectomycorrhizas was of fungal origin, the soluble protein content of the synthesized ectomycorrhizas was found to be between 10‐ and 15‐fold greater than in equivalent amounts of the non‐symbiotic tissues (short roofs and axenically grown mycelium of S. variegatus and S. bovinus). Extracts from individual ectornycorrhizas exhibited considerable esterase (EST) and peptidase (PEP) isozyme activities following PAGE and it was confirmed that diagnostic species‐specific fungal isozymes, reproducibly detected in these extracts, were present in extracts of excised sheath tissue. Acid phosphatase (ACP) isozyme activities were also detected in the ectomycorrhizas but were restricted to a single isozyme known to be common to both fungal species. In addition to the identification of taxonomically useful diagnostic fungal isozymes, the lack of detectable host PEP or ACP isozymes in these individual ectomycorrhizas, which also exhibited induced isolate‐specific EST isozymes, provides further information on the biochemical relationships in the ectomycorrhizas.
The biology of mycorrhiza in the Ericaceae
Authors: LEAKE J. R. , SHAW G. , READ D. J.
Published: April 2006

The effect of mycorrhizal infection on the uptake and distribution of iron in Calluna vulgaris was examined when plants were grown in sand supplied with different concentrations of calcium as CaC12 or CaCO3. Infection consistently caused highly significant increases in Fe concentration of Calluna shoots in CaCl2 treatments. A similar effect was obtained with CaCO3 but only in the lowest Ca treatments. Iron concentrations in roots followed the same pattern, being particularly high in all CaCl2 and in the three lowest CaCOa treatments.

Total iron contents of shoots were increased by 225% with infection in CaCl2 treatments. In the presence of CaCO3 the average increase in Fe content in shoots of infected plants was 77%, enhancement being restricted to the lowest Ca treatments (0‐50μg ml−1). In roots, the patterns were similar except that since the total Fe contents were higher than in shoots, the proportional differences between infected and uninfected plants were greater.

Mycorrhizal infection caused a significant overall increase in specific absorption rate of iron in CaCl2 treatments. In CaCO3 the specific absorption rates of mycorrhizal plants were approximately double those of uninfected plants at the four lowest Ca concentrations but at higher concentrations of the salt the reverse situation was obtained.

The nutritional implications of the results are explored, special emphasis being placed upon the possible role of mycorrhizal infection in soils of high calcium content and in situations where iron is present in sparingly soluble mineral combination with phosphates.
Uptake and translocation of α‐difluoromethylornithine, a polyamine biosynthesis inhibitor, by barley seedlings: effects on mildew infection
Authors: WALTERS D. R. , KINGHAM G.
Published: April 2006

Uptake of the polyamine biosynthesis inhibitor, α‐difluoromethylornithine (DFMO), by barley seedlings was examined. DFMO was taken up by intact roots and approached saturation at a rate of 780 mol m−12g−1d.wt. The uptake as a function of DFMO concentration in the external medium was biphasic, with Eadie‐Hofstee transformations giving Km values for system 1 uptake of 1.61 mol m−3and for system 2 uptake of 53.31 mol m−3. DFMO uptake was reduced in darkness and was greatly influenced by transpiration rate. The inhibitor was taken up from host cells by the powdery mildew fungus, Erysiphe graminis f.sp. hordei Marchal, and DFMO fed to roots, or to excised leaves at different times after inoculation, gave substantial control of mildew infection.
The control of weeds through fungi; principles and prospects
Authors: HASAN S. , AYRES P. G.
Published: April 2006

summary

The biocontrol of weeds by the introduction of exotic fungi (the classical method) has proved successful, most notably in the control of skeleton weed (Chondrilla juncea) in the wheat belt of Australia by the introduced rust, Puccinia chondrillina. There is now increasing interest in an alternative, inundative, method of weed control in which the target is controlled by a massive inoculation with a host‐specific indigenous fungal pathogen. It is proposed that through an increased understanding of host ‐ parasite interactions, in particular the enzymes and toxins that fungi use to disrupt the structure and function of weeds, screening of naturally occurring pathogens can be made more efficient. It should be possible in the immediate future to improve the efficacy of many host‐specific pathogens that currently cause little injury. In the longer term, changes in host specificity may be achieved through the techniques of genetic engineering. Meanwhile, improved formulation and methods of application can improve the range and reliability of mycoherbicides. The use of integrated control methods in which fungi are used in pairs, or in combination with either reduced rates of chemical herbicides or with arthropods, also offers hope for development. Studies of competition between plants of different species show that stunting of the weed, rather than complete kill, may be sufficient to protect crop growth. Two mycoherbicides have been successfully used in the field for almost ten years; in the next ten years we may expect to see a rapid increase in their number.

CONTENTS

Summary
201

I.
Introduction
202

II.
Principles
202

III.
Successful programmes
206

IV.
Prospects
211

V.
Conclusions
217

References
218
Comparison of disease progress curves
Authors: GILLIGAN C. A.
Published: April 2006

summary

A method of analysis, involving the comparison of parameters of nonlinear models for disease progress, is described. The method tests the effects of measures for disease control on the dynamics of botanical epidemics. It was applied to published disease progress curves for a range of host‐pathogen systems and was used to test whether treatments to control disease did so by slowing or delaying the epidemic or by reducing the asymptotic‐carrying capacity of the host population. The treatments included genetical, chemical and cultural methods including soil solarization, varietal differences and fungicide application. The logistic model was used to summarize polycyclic epidemics of Phytophthora infestans (Mont.) de Bary on potato, P. cryptogea Pethyb. & LafT. on raspberry, Fusarium oxysporum f. sp. lycopersicae (Sacc.) Snyd. & Hans, on tomato, and Puccinia recondita Rob. on wheat and triticale. The monomolecular model was used for epidemics of Sclerotium rolfsii Sacc. on carrots and S. cepivorum Berk, on garlic, that were experimentally limited to one cycle of infection. The selected model was first fitted separately to the empirical progress curve for each treatment. Subsequently, one or more common parameters were constrained to fit all treatments while the remaining parameters were separately fitted. Comparison of the changes in residual mean squares permitted approximate tests for the effects of fitting common parameters. The biological meaning of the parameters is discussed in relation to disease control. The method was sensitive in demonstrating differences amongst the treatments. Marked differences in epidemics were shown to occur when control of disease was effected by reduction in the carrying capacity or by delaying the onset of an epidemic. Few treatments, however, affected the rate parameters, especially of the logistic model.
Proteinase activity in mycorrhizal fungi
Authors: LEAKE J. R. , READ D. J.
Published: April 2006

summary

The effect of pH on the production and specific activity of the extracellular proteinase enzymes of two ecologically distinct ericoid mycorrhizal fungi is described. The proteinase of Hymenoscyphus ericae (Read), Korf & Kernan, isolated from roots of Calluna vulgaris (L.) Hull growing in soil of pH 35, was compared with a similar enzyme from an endophyte of the calcicolous alpine shrub Rhodothamnus chamaecistus (L.) Reichenb. growing in soil of pH 6.5. The fungi were grown in liquid culture at pH values ranging from 3.0 to 8.0 with pure protein, bovine serum albumin, as sole source of N.

Both fungi yielded an extracellular acid proteinase with pH optimum for activity between 20 and 30. The production and activity of these enzymes was strongly affected by pH of the culture medium. Maximum enzyme production during exponential growth occurred in both fungi at a culture pH of 4.0–5.0, whereas higher pH treatments severely inhibited enzyme production.

The acid proteinase of H. ericae was tolerant of extreme acidity and retained near‐optimal activity in solutions of pH 2.0. In contrast, the activity of the enzyme from the Rhodothamnus endophyte was almost completely inhibited at this pH. However, proteinase from the Rhodothamnus endophyte retained activity at much higher pH values than did the proteinase from H. ericae. Unlike H. ericae, the isolated endophyte of Rhodothamnus was able to grow and use protein as sole source of N at pH 7.0 and 8.0.

The effects of pH on enzyme production and upon growth of the fungi are discussed in relation to the characteristics of the environments of their host plants.
Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings
Authors: COLEMAN MARK D. , BLEDSOE CAROLINE S. , SMIT BARBARA A.
Published: April 2006

summary

Mechanistic hypotheses to explain mycorrhizal enhancement of root hydraulic conductivity (Lp) suggest that phosphorus (P) nutrition, plant growth substances and/or altered morphology may be responsible. Such ideas are based on work with VA (vesicular‐arbuscular) mycorrhizas. Since VA mycorrhizas and ectomycorrhizas differ in many respects, they may alter host plant water uptake via different mechanisms. This paper examines LT in various ectomycorrhizal associations while considering factors which are important to the VA mycorrhizal effect on Lp. Douglas fir Pseudotsuga menziesii (Mirb.) Franco] seedlings inoculated with the ectomycorrhizal fungi Laccaria bicolor (Maire) Orton and Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. and non‐inoculated seedlings infected naturally with Thelephora were grown under three low levels of P fertilization (1, 10 and 100 fim P). Seedling morphology, tissue P levels, Lp and plant growth substance levels in xylem sap were measured after nine months growth. Increased tissue P and decreased root/shoot ratio correlated with increased Lp in each of the mycorrhizal treatments. When adjusted for the effect of these two factors, Lp of Laccaria and Hebeloma seedlings was still lower than the Thelephora seedlings. In a subsequent experiment, the Lp of seedlings with Hebeloma and Rhizopogon vinicolor Smith mycorrhizas was compared to the Lp of non‐mycorrhizal seedlings (grown at 100 mM P) and no differences were found among treatments. The lack of an ectomycorrhizal effect on Lp is quite different from the enhancement of host Lp by VA mycorrhizas. Zeatin riboside concentrations of Thelephora‐ and Hebeloma‐iniected seedlings were similar, yet higher than with Laccaria. There was no relationship between plant growth substances and Lp in ectomycorrhizal Douglas fir, despite lower zeatin riboside concentrations for Laccaria‐inoculated plants.
An apparent increase in symplastic water contributes to greater turgor in mycorrhizal roots of droughted Rosa plants*
Authors: AUGÉ ROBERT M. , STODOLA ANN J. W.
Published: April 2006

summary

Using psychrometric pressure‐volume analysis, root water relations following drought were characterized in Rosa hybrida L. plants colonized by the vesicular‐arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith. Measurements were also made on uncolonized plants of similar size and adequate phosphorus nutrition. Under well‐watered conditions mycorrhizal colonization resulted in lower solute concentrations in root symplasm, and hence lower root turgors. Following drought, however, mycorrhizal roots maintained greater turgor across a range of tissue hydration. This effect was apparently not due to increased osmotic adjustment (osmotic potentials at full turgor were similar in mycorrhizal and non‐mycorrhizal roots after drought) or to altered elasticity but to an increased partitioning of water into the symplast. Symplast osmolality at full turgor was similar in mycorrhizal and non‐mycorrhizal roots but, because of their higher symplastic water percentages, mycorrhizal roots contained a greater amount of osmotic (symplastic) solutes. Drought‐induced changes in osmotic potential were observed only in mycorrhizal roots, where a 0.4 MPa decrease (relative to well‐watered controls) brought the full turgor osmotic potential of mycorrhizal roots to the same level as that of non‐mycorrhizal roots under either watering treatment.
Measurement of development of endomycorrhizal mycelium using three different vital stains
Authors: HAMEL C. , FYLES H. , SMITH D. L.
Published: April 2006

summary

The extraradical hyphae of Glomus intraradices Schenck & Smith associated with a mixture of alfalfa (Medicago sativa L. cv. Saranac) and bromegrass (Bromus inermis Leyss. cv. Tempo) were tested for metabolic activity by three enzyme staining procedures. Mycorrhizal plants were grown for 6, 9 or 12 weeks and the vital staining methods were evaluated and compared at each date. Succinate dehydrogenase activity was assessed by the reduction of nitro blue tetrazolium (nitro‐BT), and NADH diaphorase activity by the reduction of indonitrotetrazolium (INT). Fluorescein diacetate (FDA) hydrolysis was used to assess the activity of esterases in the extraradical hyphae. Percentages of intraradical hyphae that were active in alfalfa and bromegrass were also determined after staining root samples with nitro‐BT and chlorazol black E. The percentage of live intraradical infection declined with the maturing symbiosis. In contrast, no reduction with time in the percentage of extraradical hyphae that were metabolically active was shown by nitro‐BT, suggesting a different turnover for extra‐ and intraradical hyphae.

The FDA method gave the most precise estimates of enzyme activity (low SE) followed by the INT method, while the nitro‐BT method was the least precise. Different percentages of extraradical hyphae that were metabolically active were obtained with the different methods. The nitro‐BT assay deviated from the others as it did not show declining percentage of active extraradical hyphae as the symbiosis aged.
Nitrogen affects the phosphorus response of VA mycorrhiza
Authors: SYLVIA D. M. , NEAL L. H.
Published: April 2006

summary

Root colonization by vesicular‐arbuscular (VA) mycorrhizal fungi is often suppressed by phosphorus (P) additions; however, nitrogen (N) additions have been reported to both stimulate and suppress root colonization. The objective of this research was to examine colonization of Allium cepa L. roots at a range of P and N concentrations in order to clarify the effects of these nutrients on root colonization. In the first experiment, conducted under N‐limiting conditions, P addition had no effect on root colonization by Glontus etunicatum Becker & Gerdemann and increased root colonization by Gigaspora margarita Gerdemann and Trappe. In the second experiment, conducted under N‐sufficient conditions, P addition suppressed colonization by G. etunicatum. In the third experiment, P and N additions were such that tissue P:N ratios ranged from 0–03 (P limiting) to 017 (N limiting). No relationship was found between P:N ratio and root colonization for two isolates of G. etunicatum. Root colonization was not affected by P addition when plants were deficient in N but, when N was sufficient, P addition suppressed root colonization. These results demonstrate that plant N stress affects the resistance of the host root to colonization by VA mycorrhizal fungi.
Occurrence of cluster roots onMyrica ceriferaL. (Myricaceae) in water culture in relation to phosphorus nutrition
Authors: LOUIS ISABELLE , RACETTE SUZANNE , TORREY JOHN G.
Published: April 2006

summary

WhenMyrica ceriferawas grown in a number of 1/1‐strength Hoagland's solutions, each lacking one mineral nutrient, cluster roots formed only in solutions lacking phosphorus (P). In seedlings initially fertilized with various P concentrations, cluster root formation decreased with increasing P supply and was totally suppressed in solutions containing ≥ 1 mg P l−1. As total root weight did not vary significantly between P treatments, the proportion of the root system expressed as cluster roots or non‐cluster roots varied with phosphorus supply. A similar response to increasing levels of foliar‐applied P suggests that it may be internal P concentration in the plant that determines the initiation of cluster roots and not external P levels in the soil. Nitrogen, supplied as fixed dinitrogen or nitrate, did not have any effect on development of cluster roots and it appears that the capacity of actinorhizal plants to fix nitrogen by symbiotic association with a soil micro‐organism is of no significance to cluster root formation. While abundant root hair development and extensive mycorrhizal mycelium distribution in the rhizosphere may represent more efficient morphological forms of improving plant P uptake, the significance of cluster roots in relation to P nutrition and the mechanisms involved in their development warrant further investigation.
Fructan and cryoprotection in ryegrass (Lolium perenne L.)
Authors: GONZALEZ B. , BOUCAUD J. , SALETTE J. , LANGLOIS J.
Published: April 2006

summary

Changes in carbohydrate content and composition of ryegrass (Lolium perenne L.) cv. Reveille field‐grown in Normandy were investigated from May 1987 to May 1988. During the winter period, the concentrations of high DP (degree of polymerization) fructan were the lowest whilst those of ethanol‐soluble carbohydrates were the highest. Ethanol‐soluble carbohydrates also accounted for most of the non‐structural carbohydrates of four cultivars of Lolium perenne field‐grown in central France in January 1989. The accumulation of osmotically active carbohydrates during winter leads only to a small depression of freezing point and consequently, these sugars cannot be considered as efficient cryoprotectants in ryegrass.
Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open‐top chambers
Authors: WALLIN G. , SKÄRBY L. , SELLDÉN G.
Published: April 2006

summary

Rates of net photosynthesis were measured on Norway spruce,Picea abies(L.) Karst. exposed to three different concentrations of ozone for three seasons (1985–7) in open‐top chambers. The treatments were non‐filtered air + ozone (NF +), non‐filtered air (NF) and charcoal‐filtered air (CF). Ozone was added daily between 11.00–18.00 local time. The study was performed during September and October, 1987. The rate of net photosynthesis was determined using an infrared gas analyser (IRGA) connected to a small cuvette, which was equipped with an artificial light source for unilateral illumination. The measurements were made on shoots of three different age classes: current year, 1 year old and 2 years old. Measurements took place at saturating light intensity (1150 μmol m1s1), at a temperature of 16.6 ±0.7°C, and at a relative humidity of 67.5 ± 5.3%. In current‐year shoots the rate of net photosynthesis expressed on a needle‐area basis was lowest in the CF treatment and highest in the NF treatment. In 1‐ and 2‐year‐old shoots, a decreased rate of the net photosynthetic assimilation rate, expressed on a needle area basis, was observed in trees from the NF and NF+ treatment compared with that of trees from the CF treatment. The effect increased with increasing ozone concentration and shoot age. A significant increase in the rate of respiration, expressed on a dry‐weight basis, was observed in current year shoots from trees exposed to NF+. A significant decrease of the leaf conductance to carbon dioxide was obtained in 2‐year‐old shoots exposed to NF and NF+. A decrease in the content of chlorophyll was observed in 1‐ and 2‐year‐old needles from trees exposed to NF+.
Lichen physiology and air pollution
Authors: VON ARB CHRISTOPH , MUELLER CHRISTINE , AMMANN KLAUS , BRUNOLD CHRISTIAN
Published: April 2006

Samples of the lichen Parmelia sulcata Taylor were collected in the vicinity of 17 air pollution monitoring stations in the northern part of Switzerland and its bordering area. Net photosynthesis, dark respiration, and the content of [35S]‐sulphate and [35S]‐protein after cultivation with 35SO42−, as well as the chlorophyll and protein contents were measured. Mean values of dark respiration and protein content were not significantly different in the plant material from the various locations. Most of the mean values of net photosynthesis differed less than the average standard deviation. The rates of sulphate uptake and protein synthesis were lowest and chlorophyll content was highest at the most polluted sites. The values differed by a factor of 3.5‐7 between the various locations. Multiple regression analysis gave a linear correlation between the three physiological parameters [35S]‐sulphate, [35S]‐protein and chlorophyll content and a combination of the annual mean concentrations of the air pollutants NO, NO2, SO2 and O3. The highest multiple correlation coefficient (R2) was estimated for chlorophyll (0‐84). Its linear correlation coefficient (r) with NO2 alone was 0.91, and with SO2 alone 0.85.
Response of radish to multiple stresses
Authors: PELL E. J. , WINNER W. E. , VINTEN‐JOHANSEN C. , MOONEY H. A.
Published: April 2006

Experiments were conducted to determine the impact of nitrogen and ozone (O3) stress on the growth of domestic radish Raphanus sativus L. cv. Cherry Belle. Plants were grown in field chambers with sub‐, optimal and supra‐optimal levels of nitrogenous fertilizer. Chamber air was either charcoal‐filtered, or supplemented with one of two levels of O3. The highest O3 treatment resulted in significant reduction in weight of hypocotyls and roots while elevated nitrogen treatments resulted in increased weight of all plant parts. Ozone did not affect the weight of plant foliage at any nitrogen level. Plants grown with lower levels of nitrogen had less leaf biomass but the tissue accounted for a greater percentage total weight than did the foliage of higher nitrogen treatments. Relative growth rate of whole plants was not affected by O3 or nitrogen treatments reflecting compensation in response to both stresses. Ozone‐induced depression in biomass was observed in O3‐treated plants grown with higher nitrogen supply but not in those grown with limiting nitrogen. This observation could reflect compensation at the lower levels of nitrogen supply or inability to detect changes in biomass due to reduced weights of plants grown at the lowest nitrogen supply. The dry weight ratio of sink organs (hypocotyl plus root)/shoot was significantly correlated with the total non‐structural carbohydrate (TNC) content of these organs, regardless of treatment. Initially, O3 induced a significant decrease and nitrogen an increase in percent TNC of sink organs. At later sampling times, plants adjusted to stress as effects on percent TNC were no longer evident.
A new method which gives an objective measure of colonization of roots by vesicular—arbuscular mycorrhizal fungi
Authors: McGONIGLE T. P. , MILLER M. H. , EVANS D. G. , FAIRCHILD G. L. , SWAN J. A.
Published: April 2006

Previously described methods to quantify the proportion of root length colonized by vesicular‐arbuscular (VA) mycorrhizal fungi are reviewed. It is argued that these methods give observer‐dependent measures of colonization which cannot be used to compare, quantitatively, roots examined by different researchers. A modified method is described here to estimate VA mycorrhizal colonization on an objective scale of measurement, involving inspection of intersections between the microscope eyepiece crosshair and roots at magnification × 200; it is referred to as the magnified intersections method. Whether the vertical eyepiece crosshair crosses one or more arbuscules is noted at each intersection. The estimate of colonization is the proportion of root length containing arbuscules, called the arbuscular colonization (AC). The magnified intersections method also determines the proportion of root length containing vesicles, the vesicular colonization (VC), and the proportion of root length containing hyphae, the hyphal colonization (HC). However, VC and HC should be interpreted with caution because vesicles and hyphae, unlike arbuscules, can be produced in roots by non‐mycorrhizal fungi.
The effect of soil water potential on seed germination of some British plants
Authors: EVANS CERI E. , ETHERINGTON JOHN R.
Published: April 2006

‘Seeds’ of 15 species collected from a range of habitats contrasting in soil water status were germinated in soils of known matric potentials ranging from near field capacity to the permanent wilting potential (– 0.05, –0.5, –1.0 and –1.5 MPa). Germination was very sensitive to soil water potential and species responded in various ways. Some showed germination responses which correlated with the soil water status of their native habitat: none of the wetland species studied could germinate to any great extent at low soil water potentials; in contrast some species associated with drier habitats achieved high levels of germination in soils as dry as –1.0 MPa (and –1.5 MPa for one ruderal species). However, other species from drier habitats failed to germinate at low soil water potentials, and it is suggested that this may be a mechanism to avoid exposing the seedling to an unfavourable environment.
Occurrence of soluble carbohydrates on the phylloplane of maize (Zea mays L.): variations in relation to leaf heterogeneity and position on the plant
Authors: FIALA V. , GLAD C. , MARTIN M. , JOLIVET E. , DERRIDJ S.
Published: April 2006

summary

Two techniques for collection of water‐soluble substances, particularly carbohydrates, from the leaf surfaces (phylloplane) of maize (Zea mays L.) were compared in order to explain the oviposition preference of the European corn borer.

By dipping the leaves in water, smaller amounts of substances were obtained than by spraying water. The total amounts of three sugars (glucose, fructose and sucrose) collected from maize phylloplane ranged from 0.6 to 3.6 mg m−2 of leaf surface.

The quantities of these substances varied with the variety of maize, with leaf position, and with the part of the leaf. Sugar ratios on the phylloplane were quite different from those observed within the leaf.