Showing papers by "University of Adelaide published in 1988"

The retention of organic matter in soils

Abstract: The turnover of C in soils is controlled mainly by water regimes and temperature, but is modified by factors such as size and physicochemical properties of C additions in litter or root systems, distribution of C throughout the soil as root systems, or addition as litter, distribution of C within the soil matrix and its interaction with clay surfaces. Soil factors which retard mineralization of C in soils are identified from correlations of C contents of soils with other properties such as clay content and base status. The rate and extent of C mineralization depends on the chemistry of the added organic matter and interaction with clays of the microbial biomass and metabolites. The organomineral interactions are shown to depend on cation bridges involving mainly Ca in neutral to alkaline soils, Al in acid soils and adsorption of organic materials on iron oxide surfaces. The various organomineral interactions lead to aggregations of clay particles and organic materials, which stabilizes both soil structure and the carbon compounds within the aggregates.

Advances in characterization of soil structure

Abstract: Soil structure is defined as “the spatial heterogeneity of the different components or properties of soil” Aspects of soil structure which are important for plant development, soil water balance and soil workability are reviewed briefly The different types of soil structure which occur on different size scales are placed in a hierarchical order Different mechanisms give rise to the different hierarchical orders Similarly, different physical/chemical/biological processes are involved in the stabilization of the different hierarchical orders A number of methods for measuring soil structure are described Preference is given to methods involving direct observation of structural features by scanning electron microscopy and by optical scanning of impregnated sections and fracture surfaces These need to be supported by assessments of the stabilities of compound particles in water and of the mechanical strengths of compound particles as a function of water content “Good” soil structure is described as one where all the hierarchical orders are well-developed and stable The greatest lack of knowledge appears to be in the 2–100 μm size range which is too large to have been studied by colloid chemists and too small to be visible to the naked eye It is suggested that more observations of soil structure should be made in this size range, as it may hold many important clues on how to manage soil structure in the field

A discretized population balance for nucleation, growth, and aggregation

Abstract: The population balance for batch aggregation of particulate suspensions is recast in a form that may be solved simply and accurately. The transformed equation is deduced with the introduction of only one additional parameter, which is found to be a constant for all cases. The transformed equation is tested by comparison with some analytical solutions with which it is found to be in excellent agreement. In particular, the equation is shown to predict correctly the rate of change of total particle number and volume. Compatible descriptions of linear growth and nucleation are developed with similar success. The method is then applied to modeling the in vitro growth and aggregation of kidney stones (calcium oxalate monohydrate crystals). It is found that these phenomena are well described by McCabe's ΔL law, a size-independent coalescence kernel, and first-order kinetics. Simulated particle size distributions and their moments are in excellent agreement with the experimental results.

Port Pirie Cohort Study: environmental exposure to lead and children's abilities at the age of four years.

Abstract: We studied the effect of environmental exposure to lead on children's abilities at the age of four years in a cohort of 537 children born during 1979 to 1982 to women living in a community situated near a lead smelter. Samples for measuring blood lead levels were obtained from the mothers antenatally, at delivery from the mothers and umbilical cords, and at the ages of 6, 15, and 24 months and then annually from the children. Concurrently, the mothers were interviewed about personal, family, medical, and environmental factors. Maternal intelligence, the home environment, and the children's mental development (as evaluated with use of the McCarthy Scales of Children's Abilities) were formally assessed. The mean blood lead concentration varied from 0.44 μmol per liter in midpregnancy to a peak of 1.03 μmol per liter at the age of two years. The blood lead concentration at each age, particularly at two and three years, and the integrated postnatal average concentration were inversely related to deve...

A guide to Phanerozoic cold polar climates from high-latitude ice-rafting in the Cretaceous

Abstract: The high-latitude extent of warm-climate indicators at certain times in Earth history has been considered as evidence that the globe was ice-free for long intervals, despite theoretical considerations and results from numerical modelling experiments1,2 indicating that this was unlikely. One of the warmest periods, the Cretaceous, displays faunal and floral evidence for 'cool-temperate' to 'sub-tropical' conditions very near to the poles. However, our studies of Lower Cretaceous mudstones of central Australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice-rafting, implying that high-latitude ice was present at sea level. Strata of a similar origin of mid-Jurassic to mid-Cretaceous age occur on other continents that were positioned between 65° and 78° palaeolatitude. Indeed, there is a record of high-latitude ice-rafting throughout the Phanerozoic, suggesting that ice was present on Earth for much of its history, and that ice-free conditions could have been at most only episodic over the past 600 Myr.

Linkage mapping of genes controlling endosperm storage proteins in wheat

Abstract: A translocation mapping procedure was used to map gene-centromere distances for the genes controlling endosperm proteins on the short arm of each of the chromosomes 1A, 1B and 1D in wheat. The genes controlling triplet proteins (tentatively designated Tri-1) were found to be closely linked to the centromere on chromosome arms 1AS and 1DS and loosely linked to the gliadin genes (Gli-1) on the same arms. The Gli-1 genes segregated independently or were very loosely linked to their respective centromeres. The Gli-B1-centromere map distance on 1BS was also estimated using conventional telocentric mapping and the result was similar to that obtained with the translocation mapping. A simple two-step one-dimensional electrophoretic procedure is described which allows the low-molecular-weight (LMW) glutenin subunits to be separated from the gliadin bands, thus facilitating the genetic analysis of these LMW subunits. No recombination was observed between the genes (designated Glu-3) controlling some major LMW glutenin subunits and those controlling gliadins on chromosome arms 1AS and 1DS. However, in a separate experiment, the genes controlling LMW glutenin subunits on 1BS (Glu-B3) showed a low frequency of recombination with the gliadin genes.

Psychometric characteristics of the objective structured clinical examination.

Abstract: The objective structured clinical examination (OSCE) is increasingly being used as a method of clinical assessment yet its measurement characteristics have not been well documented. Evidence is accumulating that many OSCEs may be too short to achieve reliable results. This paper reports detailed psychometric analyses of OSCEs which were administered as part of a well-established final-year examination. Generalizability theory guided investigation of test reliability. At the present test length the OSCE components showed low reliabilities relative to written components. Satisfactory reliabilities could potentially be achieved if test length was increased to approximately 6 hours, a time which would create significant logistic problems for most medical schools. Several strategies for dealing with this practical problem have been explored. Firstly, it was shown that more careful selection of stations based on their psychometric characteristics can significantly improve reliability. Secondly, where rater availability is a limiting factor to increasing test length, more can be gained by using one rater per station and having more stations than using two raters per station. Finally, OSCE scores can, with advantage, be combined with other test scores which are obtained by using less resource-intensive methods. By adopting such strategies, a reliable assessment of clinical competence could be obtained in about 4 hours of testing time which was equally divided between an OSCE constructed of practical and clinical stations and a written test.

Cancer in migrants to Australia: extending the descriptive epidemiological data.

Abstract: Australia experienced a large influx of European migrants during the period 1950–1975. The descriptive epidemiological data on cancer rates within the major migrant groups, reviewed here, provide strong evidence of environmental and behavioral influences on the etiology of various cancers. The opportunity to extend the conventional type of data analysis, to include an examination of the effect of duration of residence upon cancer risk, provides further insight into cancer etiology. The possibilities of further exploring the descriptive data are also discussed, and both the desirability and the timeliness of mounting analytical studies of the Southern European migrants to Australia are emphasized.

Assessing the conscious level in infants and young children: a paediatric version of the Glasgow Coma Scale.

Abstract: The Glasgow Coma Scale is widely accepted as a measure of impaired consciousness both in clinical practice and in research In its standard form, the scale is inapplicable to infants and children below the age of 5 years We have devised a paediatric coma scale, which recognises that the expected normal verbal and motor responses must be related to the patient's age This scale has been routinely used in a paediatric teaching hospital over a 10-year period and has appeared to be satisfactory, although it is less sensitive to changes in the conscious level than the adult scale We have assessed the consistency of observer evaluation, using video tapes of infants and children exhibiting varying levels of consciousness: when conducted after formal instruction, assessments were reasonably consistent

Government and economic growth: A non-linear relationship

Abstract: Recently, various authors have examined the relationship between growth in government size and total economic growth. In each case, the authors permitted only a monotonic relationship. This paper examines the issue of a non-linear relationship between growth in government and overall growth in the economy. Government contributes to total economic output in various ways. The provision of Pigovian public goods enhances the productivity of the private sector inputs increasing total output. However, the public decision-making process can result in an inefficient quantity of public goods. The likelihood of this outcome increases with the size of government. Further negative effects are created by the revenue raising and spending mechanisms of government, and the increasing diversion of resources into ‘unproductive’ rent-seeking activities. The magnitude of these effects is likely to increase with the relative size of government. A simultaneous equations model that incorporates these different influences is developed and tested using time-series data for the United States. The estimates indicate that the non-linear model is the better for explaining the growth of total economic output.

A galE via (Vi antigen-negative) mutant of Salmonella typhi Ty2 retains virulence in humans.

Abstract: We have recently described the construction of a galE derivative of Salmonella typhi Ty2 (Ty2H1) which had a 0.4-kilobase deletion in the galE gene and was sensitive to galactose-induced lysis when cultured with greater than or equal to 0.06 mM galactose (D. M. Hone, R. Morona, S. Attridge, and J. Hackett, J. Infect. Dis. 156:167-174, 1987). We now report the selection of a rifampin-resistant, via derivative of Ty2H1, EX462. Compared with the Ty2 parent strain, EX462 was serum sensitive and highly attenuated in the mouse mucin virulence assay. When four human volunteers ingested 7 X 10(8) viable EX462, two became ill and developed a typhoidlike disease with fever and bacteremia. Blood isolates from these individuals were indistinguishable from the vaccine strain by a variety of criteria. We concluded that, even in a via background, the galE mutation was not attenuating for S. typhi in humans.

The public's view of the impact of the mass media: A test of the ‘third person’ effect

Abstract: An experiment is reported to test Davidson's (1983) hypothesis that there is a pervasive ‘third person effect' whereby people see the mass media as more likely to affect other people than it is them. Respondents were asked to judge the likely impact of three different media issues, a political campaign, the influence of violence in the media and a drink driving advertising campaign. While an issue effect was found, so that the serf was most likely to be seen as infuencible by an anti-drink driving campaign and significantly less so by media violence and politics, in all cases others were seen as being much more affected than the self. The results of the study are discussed with reference to the concept of the Ifalse consensus effect’.

Extraction and characterization of water–repellent materials from Australian soils

Abstract: SUMMARY Organic materials responsible for water–repellency in some Australian soils were extracted with an amphiphilic mixture of iso-propanol/15.7 m ammonia (7:3, v:v) in a Soxhlet apparatus, after which the water–repellent soils were rendered wettable. The successful extraction by an organic solvent system indicates that the bulk of hydrophobicity in these soils is not covalently linked to the surface of the sand. The extracted materials restored hydrophobicity on acid washed sands or ignited sands at levels comparable to the original soils. Spectroscopic and chromatographic examination of the extracted materials indicated that both free and esterified long–chain, 16–32 carbon atom, fatty acids were present with a bimodal distribution showing maxima at C16 and C22. The 13C–NMR and infrared spectra of the most hydrophobic extract suggest that hydrophobicity is caused by molecules with extensive polymethylene chains. Calculations with model compounds indicate that at least a close packed monolayer is required before measurable hydrophobicity can be detected with the molarity of ethanol droplet penetration test.

Inclusion Complexes of the Cyclomalto-Oligosaccharides (Cyclodextrins)

Abstract: Publisher Summary This chapter provides an overview of the inclusion complexes of cyclomalto-oligosaccharides (cyclodextrins). Inclusion complexes are chemical species consisting of two or more associated molecules in which one of the molecules—the “host”—forms or possesses a cavity into which it can admit a “guest” molecule, resulting in a stable association without formation of any covalent bonds. Secondary forces are alone responsible for the maintenance of the integrity of all inclusion complexes. One of the most important properties of the cyclodextrins is their ability to form complexes with a variety of organic and inorganic compounds. 1 H-Nuclear magnetic resonance (NMR) spectroscopy provided the first direct evidence of inclusion within the cyclodextrin cavity in solution. Using aromatic “guest” molecules, it was found that, on the addition of the guest, the resonances of the hydrogen atoms of the cyclodextrin situated on the inside of the cavity were shifted significantly upfield due to shielding by the aromatic guest. This chapter discusses determination of the structure of the cyclodextrins, and formation of the cyclodextrins from starch. It provides details about formation of inclusion complexes, detection of complex formation, and thermodynamics of complex formation. Kinetics of complex formation is also explained in the chapter.

Mycorrhizal growth responses: interactions between photon irradiance and phosphorus nutrition

Abstract: SUMMARY The effects of photon irradiance, phosphorus (P) supply and mycorrhizal infection [Glomus mosseae (Nicol. and Gerd) Gerdemann and Trappe] on growth and P uptake by Allium cepa L. were measured. Two experiments were carried out, one in a naturally-lit glasshouse and the other in a growth cabinet. Shade cloth was used to provide 'high' irradiance (600 and 550 yamol m-2 s-' in glasshouse and growth cabinet respectively) and 'low' irradiance (250 yamol m-2 s-1). Growth at high irradiance was associated with increases in total dry weight, root: shoot dry weight ratio and total root length and with decreases in shoot fresh weight: dry weight ratio. Mycorrhizal growth responses were lower at low irradiance and depressions were observed at high P supply and high irradiance, as well as at low irradiance. Mycorrhizal plants generally had higher shoot fresh weight: dry weight ratios than those of equivalent non-mycorrhizal plants. Mycorrhizal infection was lower in the presence of additional P in both experiments. In the glasshouse there was an interaction between low irradiance and high P, leading to very low values of fractional infection. This effect was not apparent in the growth cabinet. At high irradiance mycorrhizal plants had higher inflows than those of equivalent non-mycorrhizal plants at all levels of P, regardless of the growth response. Low irradiance had little effect on inflow into non-mycorrhizal plants, but depressed inflow into mycorrhizal plants. This reduction in inflow can be attributed in part to lower levels of infection, but an effect on P uptake by hyphae or on transport between the symbionts is also likely.

Self-cleaving viroid and newt RNAs may only be active as dimers

Abstract: Avocado sunblotch viroid (ASBV) is a 247-nucleotide, single-stranded, circular RNA1. It is considered to replicate via a rolling-circle mechanism2–4 in which circular, monomeric plus and minus RNAs act as templates for the synthesis of longer-than-unit-length precursor RNAs. Processing of these RNAs in vivo may occur by a self-cleavage reaction, as indicated by ability of dimeric, linear plus and minus ASBV RNAs to specifically self-cleave in vitro with the excision of a monomeric RNA with 5′-hydroxyl and 2′,3′-cyclic phosphodiester termini4. A similar self-cleavage reaction has also been reported to occur in an RNA transcript containing a dimeric copy of a tandemly repeated, 330-base-pair sequence of the newt genome5. Based on comparisons with self-cleaving plant viral satellite RNAs6,7, hammerhead-shaped active structures, each containing one self-cleavage site, were proposed for the plus and minus ASBV RNAs4 and the newt RNA5, but the stability of these hammerheads has been questioned4,8. Here, more stable active structures that contain two self-cleavage sites are proposed and data supporting these models are presented.

Circulation of water within wheat grain revealed by nuclear magnetic resonance micro-imaging

Abstract: Observation of water movement in situ is difficult and very few methods are available for measuring directly the motion of water. Movement of solutes or suspended particles is not a reliable guide and the use of radioactive or heavy water is limited to a few applications. Thus, although much has been inferred about the mechanism of water movement through comparatively lengthy pathways1, less is known for the shorter and more tortuous pathways within and between cells. Still more challenging is the investigation of water motion within structurally complex organs of small dimensions such as the fruits and seeds of plants, some of which behave (for water) as practically closed systems. We have observed longitudinally oriented bulk flow of water in developing grains of wheat using a pulsed gradient spin echo nuclear magnetic resonance technique combined with microscale imaging. Movement of water is associated with import of nutrients by the grain but is on too large a scale to be due to phloem transport alone. The flow observed could be associated with unloading and/or transport of nutrients in the vicinity of the vascular system. This is the first report of the observation in vivo of water movement on a sub-millimetre scale by non-invasive methods in any biological system.

Mycorrhizal associations of isolates of Sebacina vermifera

Abstract: SUMMARY Isolates of Sebacina vermifera Oberwinkler (Tremellaceae), identified by their teleomorphs, from orchid and non-orchid hosts have been examined for their mycorrhizal associations. All isolates stimulated germination of seed of species of Microtis (Orchidaceae). Three isolates from ectomycorrhizal hosts formed ectomycorrhizas on Melaleuca uneinata R. Br. ex Alton I. and other ectomycorrhizal plants. None of the orchid isolates nor an isolate which was endophytic in Phyllanthus formed ectomycorrhizas but in addition to species of Micron's they stimulated germination of one or more species of Caladenia, Cyrtostylis or Glossodia but not other terrestrial orchids. Protocorms of Microtis developed at depth in soil in the presence but not the absence of ectomycorrhizal S. vermifera on M. uneinata. Young albino plants of Microtis rara R. Br. grew for 4 months in the presence of ectomycorrhizal S. vermifera with M. uneinata but mycorrhizal albino plants on their own all died, suggesting a possible tripartite mycorrhizal association.

Two mechanisms for age‐hardening of soil

Abstract: SUMMARY Soil samples from Germany, Israel and USA were moulded at water contents around the lower plastic limit and compacted with uniaxial pressures c. 20-200 kPa. The samples were stored at constant water content. At intervals after moulding, the strengths of sub-samples were measured with a small penetrometer. The soils showed increases in strength with time. Two types of behaviour were observed and explained by a simplified theory for soil strength. With the German and Israel soils, penetrometer strength increased by the same absolute amount irrespective of compaction pressure. This indicates that new particle-particle bonds were being formed at a rate which was not affected by compaction. With the USA soils, the ratio of penetrometer strength/initial strength increased with time and was independent of compaction pressure. This indicates that existing particle-particle bonds were being reinforced by a cementation mechanism. Evidence is presented which suggests that age-hardening by this second mechanism may be inhibited by soil organic matter.

Ultrastructure of the attachment of Cryptosporidium sporozoites to tissue culture cells

Abstract: The attachment of Cryptosporidium sporozoites to Madin-Darby canine kidney (MDCK) cells was examined using transmission electron microscopy. As the anterior end of the sporozoite came into close proximity to the MDCK cell, the host cell membrane evaginated around the sporozoite, forming a parasitophorous vacuole. A dense band formed below the host cell membrane at the site nearest to the conoid. Variably electron-dense material was apparently released from the conoid and a large membrane-bound vacuole was formed in the anterior end of the sporozoite, displacing the typical anterior electron-dense organelles (rhoptries and micronemes). The outer membrane of the sporozoite pellicle then fused with the host cell membrane immediately adjacent to the conoid. The membrane surrounding the anterior vacuole was also fused with the common host-parasite membrane, forming Y-shaped membrane junctions where each limb was a unit membrane. A direct link was thereby established between the anterior vacuole of the sporozoite and the host cell cytoplasm. The anterior vacuole membrane separating the sporozoite and the host cell cytoplasm was the precursor of the feeder organelle.