Showing papers by "University of Guelph published in 1990"

A new method which gives an objective measure of colonization of roots by vesicular—arbuscular mycorrhizal fungi

Abstract: 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.

Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: 2H nuclear magnetic resonance and differential scanning calorimetry.

Abstract: Deuterium nuclear magnetic resonance spectroscopy and differential scanning calorimetry are used to map the phase boundaries of mixtures of cholesterol and chain-perdeuteriated 1,2-dipalmitoyl-sn- glycero-3-phosphocholine at concentrations from 0 to 25 mol % cholesterol. Three distinct phases can be identified: the La or liquid-crystalline phase, the gel phase, and a high cholesterol concentration phase, which we call the 0 phase. The liquid-crystalline phase is characterized by highly flexible phospholipid chains with rapid axially symmetric reorientation; the gel phase has much more rigid lipid chains, and the motions are no longer axially symmetric on the 2H NMR time scale; the 0 phase is characterized by highly ordered (rigid) chains and rapid axially symmetric reorientation. In addition, we identify three regions of two-phase coexistence. The first of these is a narrow La/gel-phase coexistence region lying between 0 and about 6 mol % cholesterol at temperatures just below the chain-melting transition of the pure phospho- lipid/water dispersions, at 37.75 OC. The dramatic changes in the *H NMR line shape which occur on passing through the phase transition are used to map out the boundaries of this narrow two-phase region. The boundaries of the second two-phase region are determined by 2H NMR difference spectroscopy, one boundary lying near 7.5 mol 5% cholesterol and running from 37 down to at least 30 OC; the other boundary lies near 22 mol 5% cholesterol and covers the same temperature range. Within this region, the gel and /3 phases coexist. As the temperature is lowered below about 30 "C, the phospholipid motions reach the intermediate time scale regime of 2H NMR so that spectral subtractions become difficult and unreliable. The third two-phase region lies above 37 OC, beginning at a eutectic point somewhere between 7.5 and 10 mol % cholesterol and ending at about 20 mol %. In this region, the La and /3 phases are in equilibrium. The boundaries for this region are inferred from differential scanning calorimetry traces, for the boundary between the La- and the two-phase region, and from a dramatic sharpening of the NMR peaks on crossing the boundary between the two-phase region and the &phase region. In this region, the technique of difference spectroscopy fails, presumably because the diffusion rate in both the La- and P-phase domains is so rapid that phospholipid molecules exchange rapidly between domains on the experimental time scale.

A Transaction Cost Analysis Model of Channel Integration in International Markets

Abstract: The authors develop a transaction cost analysis model designed to explain the channel integration choices of firms in international markets. In a test with data collected from a group of Canadian e...

Rates of Change of Soil Structure Under Different Cropping Systems

Abstract: The structure of soil can determine both the effectiveness and the impact of farming practices. Soil structure influences the extent to which crop breeding and the management of weeds, insects, disease, soil fertility, and water are manifested in increased crop yields. Soil structure also influences the loss of agricultural chemicals through erosion and leaching and can, therefore, have a significant bearing on the environmental impact of some agricultural practices.

Development of Children's Noncompliance Strategies from Toddlerhood to Age 5.

Abstract: Noncompliance strategies for asserting autonomy were examined Ss were depressed and well mothers and their children, who were 1 to 3 years old at Time 1 and 5 years old at Time 2 Data were coded from spontaneous interactions in a naturalistic setting

Footprint prediction of scalar fluxes using a Markovian analysis

Abstract: The contribution of upwind sources to measurements of vertical scalar flux density as a function of fetch (‘footprint’) is predicted using a Markovian simulation of fluid particle trajectories. Results suggest that both footprint peak position and magnitude change dramatically with surface roughness, thermal stability and observation levels. Results also indicate that the much used 100 to 1 fetch-to-height ratio grossly underestimates fetch requirements when observations are made above smooth surfaces, in stable conditions or at high observation levels.

Production of somatic and germline chimeras in the chicken by transfer of early blastodermal cells

Abstract: Cells were isolated from stage X embryos of a line of Barred Plymouth Rock chickens (that have black pigment in their feathers due to the recessive allele at the I locus) and injected into the subgerminal cavity of embryos from an inbred line of Dwarf White Leghorns (that have white feathers due to the dominant allele at the I locus). Of 53 Dwarf White Leghorn embryos that were injected with Barred Plymouth Rock blastodermal cells, 6 (11.3%) were phenotypically chimeric with respect to feather colour and one (a male) survived to hatching. The distribution of black feathers in the recipients was variable and not limited to a particular region although, in all but one case, the donor cell lineage was evident in the head. The male somatic chimera was mated to several Barred Plymouth Rock hens to determine the extent to which donor cells had been incorporated into his testes. Of 719 chicks hatched from these matings, 2 were phenotypically Barred Plymouth Rocks demonstrating that cells capable of incorporation into the germline had been transferred. Fingerprints of the blood and sperm DNA from the germline chimera indicated that both of these tissues were different from those of the inbred line of Dwarf White Leghorns. Bands that were present in fingerprints of blood DNA from the chimera and not present in those of the Dwarf White Leghorns were observed in those of the Barred Plymouth Rocks.(ABSTRACT TRUNCATED AT 250 WORDS)

Ploidy Manipulation and Gynogenesis in Fishes: Cytogenetic and Fisheries Applications

Abstract: Manipulation of fish chromosomes dates back to the early part of this century. The earliest experiments involved induction of gynogenesis with sperm inactivated by radiation or chemical treatments. Temperature or pressure shocks applied soon after fertilization resulted in the retention of the second polar body and reconstitution of diploidy; triploidy resulted from shocks to fish ova fertilized with normal sperm. More recently, it has been possible to suppress the first mitotic division offish eggs with high-pressure or -temperature treatments applied at the time of first cleavage to produce mitotic gynogenetic diploids and tetraploids. Androgenesis has been successfully induced in fish by irradiation of ova, fertilization of eggs with normal sperm, and suppression of the first mitosis with high-pressure treatments. Gynogenetic diploids have been used for cytogenetic studies of meiotic phenomena and gene mapping. The general finding to date is that the arrangement of genes on chromosomes is high...

Energy cost of absorption and metabolism in the ruminant gastrointestinal tract and liver : a review

Abstract: Contributions of various biochemical processes to overall energy expenditure in the gastrointestinal tract (GIT) and liver have been assessed in this review. The GIT and liver are responsible for a disproportionately high fraction of whole-body energy utilization. The energetic cost of Na+, K(+)-ATPase, protein synthesis and degradation, substrate cycling and urea synthesis contribute substantially to energy expenditure in the ruminant. In the splanchnic bed, these biochemical processes account for approximately 22.8% of whole-body O2 and, consequently, ATP utilization; they are influenced by several factors, including dietary composition, level of intake, age, endocrine status and physiological state. In the GIT and liver, the energetic cost of Na+, K(+)-ATPase is by far the most energetically demanding process; it is related to the active transport of substrates and the maintenance of ionic homeostasis. The high rate of protein synthesis in the GIT is associated with cellular turnover and sloughing, secretion and enzymatic action. In the liver, protein synthesis is important in the mediation of hormonal induction, which influences regulation of body systems, synthesis of plasma proteins, enzymatic and cellular turnover and detoxification of blood. Regulation of these processes and the signals involved in the differential contribution of each biochemical event are not well understood. The large contribution of these biochemical events in the GIT and liver to whole-animal energy utilization suggests that their manipulation may alter the energetic efficiency of meat, milk or wool production.

The role of the external mycelial network in the effect of soil disturbance upon vesicular−arbuscular mycorrhizal colonization of maize

Abstract: Summary This study examined the mechanism by which vesicular-arbuscular (VA) mycorrhizal colonization of young maize (Zea mays L.) 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.

Transport of a genetically engineered Pseudomonas fluorescens strain through a soil microcosm.

Abstract: Vertical soil microcosms flushed with groundwater were used to study the influence of water movement on survival and transport of a genetically engineered Pseudomonas fluorescens C5t strain through a loamy sand and a loam soil. Transport of cells introduced into the top 1 cm of the vertical soil microcosms was dependent on the flow rate of water and the number of times microcosms were flushed with groundwater. The presence of wheat roots growing downward in the microcosms contributed only slightly to the movement of P. fluorescens C5t cells to lower soil regions of the loamy sand microcosms, but enhanced downward transport in the loam microcosms. Furthermore, the introduced P. fluorescens C5t cells were detected in the effluent water samples even after three flushes of groundwater and 10 days of incubation. As evidenced by a comparison of counts from immunofluorescence and selective plating, nonculturable C5t cells occurred in day 10 soil and percolated water samples, primarily of the loamy sand microcosms. Vertical soil microcosms that use water movement may be useful in studying the survival and transport of genetically engineered bacteria in soil under a variety of conditions prior to field testing.

Lactate and potassium fluxes from human skeletal muscle during and after intense, dynamic, knee extensor exercise.

Abstract: This study examines lactate and K+ fluxes from muscle to blood during and after intense exercise. Ten men performed exhaustive dynamic exercise (mean load 65 W, mean duration 3.18 min) with the knee extensors of one leg. The mean lactate efflux was 15.5 (range 8.9-24.0) mmol min-1 at exhaustion, and it was linearly related to the lactate gradient. A linear relationship was also obtained if the H+ gradient was taken into account. Muscle pH decreased from 7.14 at rest to 6.71 (range 6.50-6.87) at exhaustion. At rest and during late recovery blood lactate was distributed across the erythrocyte membrane according to the membrane potential (intra-/extracellular ratio of 0.5), but during rapid lactate release this ratio decreased to 0.2. In-vitro experiments demonstrated a time constant of 1.2 min for lactate efflux from the erythrocytes. Approximately 70% of the K+ ions released from the muscle to the blood accumulated in the plasma; the rest were taken up by other tissues. However, erythrocytes were not involved as a dilution space. The small change in erythrocyte K+ concentration was due to cellular volume changes. During recovery the kinetics of K+ reuptake by the muscle were described by a very fast (less than 1 min) and a slow component (greater than 1 min): the magnitude of the former was equivalent to what had accumulated in the plasma. Individuals displayed a wide range of intramuscular lactate concentrations and pH values at exhaustion. Further, the pH changes were not as extreme as previously reported, suggesting that pH may not be the only factor involved in the fatigue process. A possible role for the potassium shifts as a limiting factor for muscle function is discussed.

Effect of degree of soil disturbance on mycorrhizal colonization and phosphorus absorption by maize in growth chamber and field experiments

Abstract: SUMMARY Prior studies have established that phosphorus absorption by maize from undisturbed soil is greater than from soil which has been disturbed since the previous period of growth. Those experiments were conducted under controlled conditions and with only two disturbance treatments, namely disturbance of the soil by hand sufficient that it will pass a 5 mm sieve, and no disturbance at all. We present here two experiments in which additional treatments of intermediate degrees of disturbance are included. In a growth chamber experiment, cutting the soil into 1, 2 or 4 cm cubes reduced the phosphorus absorption and shoot dry matter, but the reduction was not as great as that after hand disturbance of the soil. In a field experiment, the phosphorus absorption and shoot dry matter found in a conventional tillage and no-till treatments were less than in hand-planted no-till plots, but greater than with severe soil disturbance. In both experiments increases in shoot dry mass and shoot phosphorus concentration in the less disturbed treatments were not accompanied by an increase in mycorrhizal colonization. This is inconsistent with earlier studies in which colonization was greater in undisturbed soil. Since it has now been demonstrated that increased colonization is not a necessary component in the process whereby lack of disturbance results in improved plant performance, the role of mycorrhizas in this effect should be reconsidered. If mycorrhizas are important in this respect then this can only be by means of changes in the external mycelium. However, without experimental confirmation this interpretation is speculative.

A review of the physiological significance of hypertonic body fluids on feed intake and ruminal function: salivation, motility and microbes.

Abstract: Mechanisms exist in the ruminant to detect changes in osmolality and volume of plasma during feeding to maintain fluid and electrolyte homeostasis. Feed intake during a meal can be limited by the rise in osmolality of ruminal fluid, which is sensed in the wall of the rumino-reticulum. Ruminal microbes appear to be resilient to the short-term changes in ruminal fluid tonicity, but in vitro growth rates are inhibited when the tonicity of the culture medium is increased beyond physiological levels. Although mixing contractions of the rumen are not inhibited by the normal increases in tonicity of ruminal fluid, time to first rumination is increased. This aspect of motility requires further research. The tonicity of plasma increases toward the end of a large meal as a consequence primarily of absorption of VFA and Na+ from the rumen and fluid shifts into the gut. This hypertonicity is sensed centrally to inhibit parotid secretion by a reduction in the parasympathetic stimulation to the gland. Increases in animal production may result from future research directed toward developing ways of counteracting these negative effects of hypertonicity in body fluids on feed intake and ruminal function.

Heat Increment: A Static or Dynamic Dimension in Bioenergetic Models?

Abstract: Bioenergetic models of growth endeavor to integrate food-processing transactions with energy expenditures imposed by abiotic and biotic factors. Some components of these models have lagged behind others in the synthesis of new information. A case in point is heat increment, a measure of metabolic work primarily for the postabsorptive processes that follow the ingestion of food. Importantly, the energy requirements for grasping, chewing, and swallowing food are technically distinct from those for heat increment but are experimentally difficult to separate from them. In order to take special account of these mechanical aspects, we suggest modifying the term “heat increment” (also known as specific dynamic action) to the less-precise “apparent heat increment.” Bioenergetic models invariably incorporate the assumption that apparent heat increment, relative to food intake, is independent of other variables. Laboratory studies have revealed that apparent heat increment is not always a fixed proportion ...

Low temperature sweetening in susceptible and resistant potatoes: starch structure and composition

Abstract: Starch isolated from ND 860–2 potatoes, which were resistant to chillsweetening, had higher amylose and lower amylopectin as well as a higher crystallinity as compared to starch isolated from Norchip potatoes, which were susceptible to low temperature sweetening. ND 860–2 starch exhibited greater resistance to α-amylase attack and amorphous swelling as well as higher gelatinization temperatures and onset swelling temperatures than starch isolated from Norchip. Examination of starch granule structure using bright field light microscopy indicated crystalline concentric rings in ND 860–2 not seen in Norchip. Scanning electron microscopy of granules incubated with a-amylase indicated more intact ND 860–2 starch granules compared to Norchip. These data strongly suggest that starch granule composition is a factor differentiating the low-temperature sweetening sensitive cultivar from the resistant potato seedling.

Fuzzy information representation and processing in conventional GIS software: database design and application

Abstract: Currently used methods for representing geographical information are inadequate because they do not tolerate imprecision. This leads to information loss and inaccuracy in analysis. Such expressive inadequacy is largely due to the underlying membership concept of classical set theory. To improve information processing in GIS research and application, an alternative membership concept is required. In this paper, we explore the inadequacy imposed upon geographical information representation by classical set theory and address the problems of information loss. A fuzzy relational data model is defined which is more representative for geographical information. A GIS database for agricultural land resource management is created by using the data model and a new technique for assessing land suitability is developed. The fuzzy representation largely facilitates data analysis in this GIS. The methods are tested with data from North Java, Indonesia using a vector-based GIS software package, Arc Info, and the analysi...

Short spacings and polymorphic forms of natural and commercial solid fats: A review

Abstract: Short spacings refer to the cross sectional packing of the hydrocarbon chains. They are independent of chain length. Short spacings are widely used for characterizing the various polymorphic forms. Fats can crystallize into four polymorphic forms, i.e., sub-α, α, β′ and β. These polymorphic forms differ in their chain packing and thermal stability. The β′ form is also known to exhibit several intermediate polymorphic forms. The nomenclature for the polymorphic forms has generated a great deal of confusion over the years. Several researchers have reported on the polymorphic forms of pure triglycerides. Similar polymorphs have sometimes been described by different names. Currently, the nomenclature proposed by Larsson [Larsson, K.,Acta Chem. Scand. 20:2256 (1966)] is being widely used. Much of the earlier work on polymorphism has been obtained by studying simple purified substances. The listing of short spacings for natural and commercial fats presented in this paper will be beneficial to researchers working in this field.

Metal-Binding Characteristics of the Gamma-Glutamyl Capsular Polymer of Bacillus licheniformis ATCC 9945.

Abstract: The metal-binding affinity of the anionic poly-γ-d-glutamyl capsule of Bacillus licheniformis was investigated by using Na+, Mg2+, Al3+, Ca2+, Cr3+, Mn2+, Fe3+, Ni2+, and Cu2+. Purified capsule was suspended in various concentrations of the chloride salts of the various metals, and after dialysis the bound metals were analyzed either by graphite furnace atomic absorption spectroscopy or by inductively coupled plasma-mass spectrometry. Exposure of purified capsule to excess concentrations of Na+ revealed it to contain 8.2 μmol of anionic sites per mg on the basis of Na binding. This was confirmed by titration of the capsule with HCl and NaOH. Other metal ions were then added in ionic concentrations equivalent to 25, 50, 75, 100, 200, and 400% of the available anionic sites. The binding characteristics varied with the metal being investigated. Addition of Cu2+, Al3+, Cr3+, or Fe3+ induced flocculation. These metal ions showed the greatest affinity for B. licheniformis capsule in competitive-binding experiments. Flocculation was not seen with the addition of other metal ions. With the exception of Ni2+ and Fe3+ all capsule-metal-binding sites readily saturated. Ni2+ had low affinity for the polymer, and its binding was increased at high metal concentrations. Fe3+ binding resulted in the development of rust-colored ferrihydrite which itself could bind additional metal. Metal-binding characteristics of B. licheniformis capsule appear to be influenced by the chemical and physical properties of both the capsule and the metal ions.

A review of recent studies on the metabolism of exogenous and endogenous malondialdehyde

Abstract: 1. The generation of malondialdehyde (MDA), a mutagenic product of the oxidative decomposition of highly unsaturated fatty acids in vivo, is increased by exposure to certain environmental oxidants and xenobiotics. 2. This increase is reflected in enhanced excretion of several MDA derivatives in the urine. The main urinary metabolites of MDA have been identified as N-epsilon-(2-propenal)lysine and its N-alpha-acetyl ester. 3. Two minor metabolites have been identified as enaminals formed by reactions with the phospholipid bases serine and ethanolamine. A further MDA metabolite has been identified as a cyclized adduct with guanine. 4. These urinary compounds reflect the turnover of proteins, phospholipids and nucleic acids that have been modified by reactions with MDA in vivo. Monitoring of the urinary adduct with guanine may provide a practicable method of assessing the effect of xenobiotics and other factors on in vivo lipid peroxidation. 5. The proportion of total MDA in the diet, blood, urine and solid tissues that exists in the free state appears to be negligible. 6. Chronic oral administration of the enol Na salt of MDA to animals produced no significant pathology except for dose-dependent lesions of hepatic nuclei. Nuclear abnormalities in cultured rat skin fibroblasts were seen at intracellular concentrations as low as 10(-7) M.

Characteristics of a Membrane-Associated Lipoxygenase in Tomato Fruit

Abstract: Microsomal membranes isolated from the pericarp of maturegreen tomato (Lycopersicon esculentum) fruit rapidly metabolize exogenous radiolabeled linoleic acid into fatty acid oxidation products at 22°C. The reaction is strongly inhibited by n-propyl gallate, an inhibitor of lipoxygenase. The membranes also rapidly metabolize 16:0/18:2* phosphatidylcholine into radiolabeled oxidation products that comigrate on TLC plates with those formed from free linoleic acid. At 30°C, the formation of fatty acid oxidation products from 16:0/18:2* phosphatidylcholine is slower, and there is an initial accumulation of radiolabeled linoleic acid that is not evident at 22°C, which can be attributed to the action of lipolytic acyl hydrolase. Radiolabeled phosphatidic acid and diacylglycerol are also formed during metabolism of 16:0/18:2* phosphatidylcholine by the microsomal membranes, and there is no breakdown of either linoleic acid or phosphatidylcholine by heat-denatured membranes. When Triton X-100 treated membranes were used, the same patterns of metabolite formation from radiolabeled linoleic acid and 16:0/18:2* phosphatidylcholine were observed. Thus, the enzymes mediating the breakdown of these radiolabeled compounds appear to be tightly associated with the membranes. Collectively, the data indicate that there is a lipoxygenase associated with microsomal membranes from tomato fruit that utilizes free fatty acid substrate released from phospholipids. The microsomal lipoxygenase is strongly active over a pH range of 4.5 to 8.0, comprises approximately 38% of the total (microsomal plus soluble) lipoxygenase activity in the tissue, has an apparent Km of 0.52 millimolar and an apparent Vmax of 0.186 millimoles per minute per milligram of protein. The membranous enzyme also cross-reacts with polyclonal antibodies raised against soybean lipoxygenase-1 and has an apparent molecular mass of 100 kilodaltons.

Insect pollinators and sustainable agriculture

Abstract: Underestimation of the pivotal role played by managed and native insect pollinators is a key constraint to the sustainability of contemporary agricultural practices. The economic value of such insects to pollination, seed set, and fruit formation greatly outweighs that suggested by more conventional indices, such as the value of honey and wax produced by honeybees. Although the European honeybee has been widely regarded as the single most important pollinating species, the increasing spread of trachael and Varroa mites and Africanized bees threatens the distribution and magnitude of traditional honeybeekeeping enterprises in North America. A number of other bee and insect pollinators, such as orchard bees, bumblebees, and squash bees, which are not affected by either the mites or the Africanized bees, are considered as likely candidates for management and use in commercial agriculture. An additional role can be played by native or wild pollinators, provided that attention is given to curtailing of population losses caused by both inadvertent insecticide poisoning and habitat destruction. To ensure a reliable source of pollinators, both managed and native, a more comprehensive strategy for management of crop pollination is needed. Elements of this strategy include an increased understanding of the biology and ecology of pollinating insects, as well as providing appropriate nesting habitat, and ensuring the availability of alternative sources of “forage” to sustain populations when the target crops are not in bloom. Examples are discussed to illustrate how private initiatives and changes to public policy can enhance pollinator habitat, and ultimately, agricultural productivity.