Contrasting ability of deep and shallow rooting rice genotypes to grow through plough pans containing simulated biopores and cracks

Plant and Soil - Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research...     

Quantal secretion and response lag demonstrated in single rat neutrophils

The release of 9-aminoacridine loaded into neutrophil granules has been monitored using quantitative fluorescence microscopy of individual rat neutrophils. Within the granule, the fluorescence of the dye was substantially quenched, but release into the surrounding medium restored fluorescence. From kinetic analysis of the increase in fluorescence it was shown that secretion from a single neutrophil in response to a low concentration of chemotactic peptide occurred in 'bursts'. Each 'burst' of secretion was of equal size and kinetics, which were equal to the size and kinetics of the smallest evoked response possible. A significant time-lag of 5-10 s between the arrival of the stimulus at the cell and the onset of secretion was recorded. It was therefore concluded that secretion from neutrophils was the result of release of quantal amounts of dye following a delay period.     

Reversible cell damage by T-cell perforins. Calcium influx and propidium iodide uptake into K562 cells in the absence of lysis.

The non-lethal effects of the lymphocyte-derived pore-forming toxin perforin on the human erythroleukaemia cell line K562 were investigated. By using the fluorescent Ca2+ indicator fura-2, perforin was shown to cause intracellular Ca2+ concentration to rise transiently into the micromolar range in the absence of cell death. By fluorescence-activated cell sorting it was demonstrated that K562 cells took up the membrane-impermeant nuclear stain propidium iodide (PI) when exposed to non-lethal doses of perforin. The permeability to PI was short-lived, confirming the transience of the perforin pore. Analogies with non-lethal effects and recovery processes occurring in nucleated cells exposed to the membrane-attack complex of complement are drawn.     

Spatiotemporal inseparability in early visual processing

We examine the implications of significant inseparable behaviour in centre-surround retinal cell types. From the form of a spatiotemporal centre-surround (CS) model which agrees qualitatively with physiological observations, we find that the sustained/transient dichotomy is a poor distinction for X-type/Y-type retinal ganglion cells since both exhibit inseparability. Static centre-surround models and spatiotemporal separable models are not valid for time-varying stimuli. Our results contradict the models for X- and Y-type ganglion cells proposed by Marr and Hildreth (1980) and Marr and Ullman (1981), and raise doubts about the physiological validity of Marr's zerocrossing theory. The CS filter is an attractive precursor to the extraction of 2-d motion information.     

The effect of immunization against somatostatin on growth rates and growth hormone secretion in the chicken

The effect of both active passive immunization against somatostatin on growth rate and growth hormone levels was studied in chickens. Passive immunization against somatostatin by administration of antiserum had no effect on rate of growth of chickens and no persistent effect on circulating growth hormone (GH) levels. In acute experiments, administration of anti-somatostatin serum caused a marked elevation of GH levels in chickens at both 4 and 8 weeks of age, but the relative stimulation was greater in the older birds. Active immunization against somatostatin significantly stimulated growth rate in chickens, but was not shown to have a clear effect on circulating GH levels. These data suggest that somatostatin control over GH secretion may not be fully developed in the chicken at 4 weeks of age, but that immuno-neutralization of somatostatin can produce an increase rate of growth in chickens similar to that seen in mammals.     

Mechanical properties of vesicles. I. Coordinated analysis of osmotic swelling and lysis.

To determine how transmembrane osmotic gradients perturb the structure and dynamics of biological membranes, we examined the effects of medium dilution on the structures of osmolyte-loaded lipid vesicles. Our preparations were characterized by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR) spectroscopies. Populations of Escherichia coli phosphatidylethanolamine (PE) or dioleoylphosphatidylglycerol (DOPG) vesicles prepared by the pH jump technique were variable and polymodal in size distribution. Complex and variable structural changes occurred when PE vesicles were diluted with hypotonic buffer. Such vesicles could not be used as model systems for the analysis of membrane mechanical properties. NaCl-loaded, DOPG vesicles prepared by extrusion through 100 nm (diameter) pores were reproducible and monomodal in size distribution and unilamellar, whereas those prepared by extrusion through 200-, 400-, or 600-nm pores were variable and polymodal in size distribution and/or multilamellar. Time and pressure regimes associated with osmotic lysis of extruded vesicles were defined by monitoring release of carboxyfluorescein, a self-quenching fluorescent dye. Corresponding effects of medium dilution on vesicle structure were assessed by DLS spectroscopy. These experiments and the accompanying analysis (Hallett, F.R., J. Marsh, B.G. Nickel, and J.M. Wood. 1993. Biophys. J. 64:000-000) revealed conditions under which vesicles are expected to reside in a consistently strained state.     

Biophysical studies of infectious pancreatic necrosis virus.

The molecular weight of infectious pancreatic necrosis virus (IPNV) has been determined by analytical ultracentrifugation and dynamic light scattering. The sedimentation coefficient of the virus was found to be 435S. The average value for molecular weight is (55 +/- 7) x 106. The virus genome consists of two segments of double-stranded RNA (molecular weights, 2.5 x 106 and 2.3 x 106), which represents 8.7% of the virion mass. The capsid protein moiety of IPNV consists of four species of polypeptides, as determined by polyacrylamide gel electrophoresis. The number of molecules of each polypeptide in the virion has been determined. There are 22 molecules of the internal polypeptide alpha (molecular weight, 90,000), 544 molecules of the outer capsid polypeptide beta (molecular weight, 57,000), and 550 and 122 molecules, respectively, of the internal polypeptides gamma1 (molecular weight, 29,000) and gamma2 (molecular weight, 27,000). IPNV top component contains only the beta polypeptide species, and its molecular weight is estimated to be 31 x 106. The hydrodynamic diameter and electron microscopic diameter (calculated by catalase crystal-calibrated electron microscopy) of IPNV was compared with those of reovirus and encephalomyocarditis virus. Due to the swelling of the outer capsid, reovirus particles were found to be much larger when hydrated (96-nm diameter) than when dehydrated (76-nm diameter), having a large water content content and low average density. In contrast, IPNV particles are more rigid, having nearly the same average diameter under hydrous (64 nm) as under anhydrous conditions (59.3 nm). Encephalomyocarditis virus has a very low water content and does not shrink at all when prepared for electron microscopy.     

Activation of upper airway muscles before onset of inspiration in normal humans

Animal studies have shown activation of upper airway muscles prior to inspiratory efforts of the diaphragm. To investigate this sequence of activation in humans, we measured the electromyogram (EMG) of the alae nasi (AN) and compared the time of onset of EMG to the onset of inspiratory airflow, during wakefulness, stage II or III sleep (3 subj), and CO2-induced hyperpnea (6 subj). During wakefulness, the interval between AN EMG and airflow was 92 +/- 34 ms (mean +/- SE). At a CO2 level of greater than or equal to 43 Torr, the AN EMG to airflow was 316 +/- 38 ms (P < 0.001). During CO2-induced hyperpnea, the AN EMG to airflow interval and AN EMG magnitude increased in direct proportion to CO2 levels and minute ventilation. During stages II and III of sleep, the interval between AN EMG and airflow increased when compared to wakefulness (P < 0.005). We conclude that a sequence of inspiratory muscle activation is present in humans and is more apparent during sleep and during CO2-induced hyperpnea than during wakefulness.     

Thinking systemically about ecological interventions: what do system archetypes teach us?

To address the need for more holistic approaches to ecological management and restoration, we examine ecosystem interventions through the lens of systems thinking and in reference to systems archetypes, as developed in relation to organizational management in the business world. Systems thinking is a holistic approach to analysis that focuses on how a system's constituent parts interrelate and how systems work over time and within the context of larger systems. Systems archetypes represent patterns of behavior that have been observed repeatedly. These archetypes help relate commonly observed responses to environmental problems with their effect on important feedback processes to better anticipate connections between actions and results. They highlight situations where perceived solutions actually result in worse or unintended consequences, and where changing goals may be either appropriate or inappropriate. The archetypes can be applied to practical examples, and can provide guidance to help make appropriate intervention decisions in similar circumstances. Their use requires stepping back from immediately obvious management decisions and taking a more systemic view of the situation. A catalog of archetypes that describe common patterns of systems behavior may inform management by helping to diagnose system dynamics earlier and identifying interactions among them.     

A framework for modelling soil structure dynamics induced by biological activity

Soil degradation is a worsening global phenomenon driven by socio‐economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil–crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil–plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil–crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil.