Kinetic analysis of reversible closed bicyclic enzyme cascades covering the whole course of the reaction

A kinetic analysis of the closed bicyclic enzyme cascades is presented.

• 1.1. It includes the dependence on time from the onset of the reaction, of the concentration of the modified and unmodified enzyme species involved and the time course equations of the modificational fractions of the interconvertible enzymes.
• 2.2. The transient phase equations obtained allow the definition of new regulatory modification properties.
• 3.3. The expressions for concentrations of the unmodified and modified forms of the interconvertible enzymes, as well as those of the fractional modifications in the steady state are derived as particular cases of the general equations.
• 4.4. These steady state expressions coincide with those obtained by other authors.
• 5.5. The analytical results obtained are discussed in relation to the Escherichia coli glutamine syntethase cascade.

     

The nature of the fluid boundary layer and the selection of parameters for benthic ecology: reply to Lamouroux

• 1 The near bed flow equations and definitions given originally by Carling (1992) are reviewed and are shown to be correct and unambiguous. The theoretical assumptions inate in deriving the governing equations are violated in non-uniform, unsteady flow, such as occurs in shallow flow over rough beds, but in practice results obtained from log-law models are often not significantly different from those derived from functions purporting to represent large-scale roughness. This point was made carefully in the original paper.
• 2 More complex approaches now exist for modelling gradually varying, slightly non-uniform flow which are modifications of uniform flow models. These are not readily applicable to field data commonly available to ecologists, however, and generally give little additional insight. Advances are only likely to be made when turbulent flow structure is better understood.

     

Kinetic analysis of the michaelis-menten mechanism in which the substrate and the product are unstable

• 1.1. A kinetic analysis of the Michaelis-Menten mechanism for the case in which both the substrate and the product are unstable, either spontaneously or as the result of the addition of a reagent, has been made.
• 2.2. The explicit time course equations of the immediate product and the species into which it subsequently is transformed have been derived under the conditions of rapid equilibrium and limiting substrate concentration.
• 3.3. The validity of these equations has been checked using numerical simulations.
• 4.4. The kinetic data analysis which we suggest is based on the time progress curves of the product or, in the case in which the product accumulation cannot be monitored experimentally, on the time progress curve of the species into which the immediate product is transformed.
• 5.5. This analysis allows the determination of the rate and the equilibrium constants if adequate experimental results are available.
• 6.6. We have chosen a numerical example, with which we illustrate the procedure of the kinetic data analysis by simulating some curves with assumed experimental errors.

     

Spatial patterning of the spruce budworm

The spatial and temporal distribution of the spruce budworm is modelled by a nonlinear diffusion equation. Two questions are considered:

1. What is the critical size of a patch of forest which can support an outbreak?
2. What is the width of an effective barrier to spread of an outbreak?

Answers to these questions are obtained with the aid of comparison methods for nonlinear diffusion equations.     

Modelling the effects of field spatial scale and natural enemy colonization behaviour on pest suppression in diversified agroecosystems

1. Diversifying agroecosystems by establishing or retaining natural vegetation in and around crop areas has long been recognized as a potentially effective means of bolstering pest control as a result of attracting more numerous and diverse natural enemies, although outcomes are inconsistent across species.
2. Little is known about the underlying mechanisms driving such differences in species responses, creating challenges for determining how best to manage landscapes for maximizing environmental services such as biological control.
3. The present study addresses gaps in our understanding of the link between noncrop vegetation in field margins and pest suppression by using a system of partial differential equations to model population‐level predator–prey interactions, as well as spatial processes, aiming to capture the dynamics of crop plants, herbivores and two generalist predators.
4. We focus on differences in how two predators (a carabid and a ladybird beetle) colonize crop fields where they forage for prey, examining differences in how they move into the fields from adjacent vegetation as a potential driver of differences in overall pest suppression.
5. The results obtained demonstrate that predator colonization behaviour and spatial scale are important factors with respect to determining the effectiveness of biological control.

     

The metabolic output of avian (Sturnus vulgaris,Calidris alpina) adipose tissue liver and skeletal muscle: Implications for BMR/body mass relationships

• 1.1. The oxygen uptake rate of avian adipose tissue, liver and skeletal muscle slices were measured.
• 2.2. The energy consumption of fat was less than one tenth that of liver and muscle.
• 3.3. Thus, interspecific allometric equations for the prediction of basal metabolic rate from body mass will not be accurate throughout the avian annual cycle unless changes in body composition are taken into account.

     

Environmental drivers of macroinvertebrate communities in high Arctic rivers (Svalbard)

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Evaluation of the cold tolerance of Saccharum spontaneum L. clones with different ploidy levels on the basis of morphological and physiological indices

• Saccharum spontaneum L. is one of the most important germplasm resources for modern sugarcane breeding. Exploring the cold tolerance of S. spontaneum clones with different ploidy levels and screening for cold‐tolerant material can be helpful in parent selection for breeding cold‐tolerant sugarcane.
• Morphological indices, leaf ultrastructure and physiological indices were used to evaluate the cold tolerance of 36 S. spontaneum clones with different ploidy levels (2n = 40, 48, 54, 60, 64, 78, 80, 88, 92 and 96).
• The morphological indices of S. spontaneum clones with different ploidy levels were positively correlated with ploidy. Under low‐temperature stress, the chloroplast and mitochondrial structures of the clones with high ploidy were more severely damaged than were those of clones with low ploidy. A comprehensive evaluation of the physiological indices showed that the 36 S. spontaneum clones could be divided into four categories: strongly cold tolerant, cold tolerant, moderately cold tolerant and cold sensitive. Correlation analysis of the morphological indices and cold tolerance revealed a significant negative correlation between cold tolerance and ploidy. On the basis of the morphological and physiological indices, optimal stepwise regression equations that can be used for the selection of cold‐tolerant S. spontaneum resources were established.
• The S. spontaneum clones with low ploidy are more cold tolerant than those with high ploidy. Clones 12‐37, 13‐10 and 12‐23 are strongly cold‐tolerant germplasm resources, which suggests these germplasm sources have high potential for use in breeding cold‐tolerant sugarcane.

     

Design and test of a generic cohort model of soil organic matter decomposition: the SOMKO model

• 1 SOMKO is a new simulation model of soil organic matter (SOM) dynamics aimed at predicting long‐term and short‐term SOM dynamics based on a mechanistic approach focusing on microbes as the key agents of decomposition.
• 2 SOM is partitioned into cohorts and chemical quality pools (classified by age and chemical composition), the microbial community processes are explicitly represented, and the C : N stoichiometric constraints are accounted for through a new mechanism of offer and demand.
• 3 The analysis of model equations shows that: (1) SOM C : N cannot decrease below microbial C : N; and (2) the nitrogen limitation of decomposition depends on SOM C : N, microbial biomass and soil mineral nitrogen. First tests of the model show good qualitative behaviour for simulating the dynamics of short‐term litter‐bag type decomposition, long‐term SOM increase, pulsed mineral nitrogen production, the priming effect due to easily decomposable carbon addition, and the effects of vegetation clearance and climate change on SOM. Simulations are in good agreement with long‐term experimental data.
• 4 SOMKO is an integrated component of the coupled soil–vegetation models within the ETEMA (European Terrestrial Ecosystem Modelling Activity) framework. Future extensions of this work include: (1) estimating microbial parameters from specific experiments; (2) spatial distribution of SOMKO in multistrata models; and (3) implementing nitrification/denitrification processes, phosphorus limitation and microfaunal activity.

     

The role of mechanical shear and cavitation on the behaviour of molds

The morphology of filamentous microorganisms does essentially affect the production of metabolites. Agitating conditions may affect the morphology and for this reason the production of metabolites too. The following parameters it was found to have an influence:

• Reynolds mixing number
• impeller blade tips velocity
• mean shear stress close to the impeller
• impeller power consumption per unit volume
• cavitation pressure drop

It were presumed three mechanisms for the mechanical effect on the microorganisms:

• 1 the direct impact of the impeller blades on the microorganisms-collision
• 2 the shear stress in the liquid phase
• 3 a sharp pressure decrease behind the impeller blades-cavitation

Mathematical relationships are developed for the different mechanisms.Using Aspergillus niger it is shown what morphological and physiological states of this microorganism are caused by mechanical straining and the conditions for the maximal production of citric acid are studied. Requirements for scale-up are discussed.     

The occurrence of benthos deep in the substratum of a stream

• 1 The vertical distribution of the benthic fauna of the Speed River, Ontario, was studied over a 13-month period from October 1970 to October 1971. Various physical and chemical parameters of this interstitial environment were also measured.
• 2 Several new techniques for sampling the interstitial environment of rivers wert devised. These methods and their relative efficiencies are considered.
• 3 The validity of the terms ‘hyporheal’ and ‘hyporheic’ are discussed and the term ‘hyporheos’ is offered to replace the former.
• 4 A brief resume of interstitial sampling methods is given with comments on their limitations for sampling deep heterogeneous substrates.
• 5 Chemical parameters are thought to be more important in the control and distribution ofthe fauna than physical parameters.
• 6 It is suggested that many larvae of stream-dwelling chironomids have over-wintering stages when they penetrate deep into the substrate to: (a) actively feed on the trapped organic detritus; (b) follow an optimum temperature for development.
• 7 It is suggested that the shape of an organism determines its success as a hypo-rheic form and examples are given.
• 8 The numbers of animals oecurring in the sub-benthic populations are shown to be very large indeed. For the Speed River, estimates of between 184,760 and 797,960 animals/m^ are made for different times of the year. Dry weight biomass is estimated o t vary between 30 9 g and 253-2 g/m^ throughout the year.
• 9 Sub-benthic or hyporheic populations are shown to exist in at least three other Canadian rivers. Some ofthe animals found are shown to be common to two or more of these rivers.
• 10 The inefficiencies of many conventional benthic samplers in sampling the total biomass of certain streams with hyporheic populations is discussed.

     

Study of two forms of the adult Stenocranus minutus

• 1 In studies on Stenocranus minutus, two winged forms of adults have been observed, macropterous and sub-macropterous. Macropterous individuals, with extra-long wings, have not been previously observed or described. Probably only the macropterous form disperses by flight.
• 2 The two forms differ in their wing lengths, intensity and extent of pigmentation.
• 3 The rate of maturation differs in the two forms. In macropters, maturation is delayed; the period of oviposition is shorter and they are less fecund.
• 4 Macropters do not live as long as sub-macropters.
• 5 The macropters weigh less than the sub-macropters.
• 6 Under laboratory conditions, both forms can hop but the macropterous forms fly for a longer time than the sub-macropters.
• 7 At 25°C, more macropterous forms were produced on wilting Dactylis than on green, succulent Dactylis.
• 8 Dispersal of field population was inferred from changes in proportions of the two forms and by simultaneous occurrence of macropters in aerial suction traps.
• 9 The macropterous forms of S.minutus migrate a few weeks after emergence while still immature and migration coincides with drying up of host plant, Dactylis glomerata L.
• 10 Relatively high temperature, low wind speeds and a small number of hours of sunlight seem to favour dispersal by flight in S.minutus.

     

Successional status of trees in gallery forest along the river Rhine

Abstract. 20 alluvial forest stands of different ages along the river Rhine in central Alsace, France, are described. A natural complex landscape occurs which is formed by erosion activity of the river. Recent human impact (canal construction, cutting) has affected river hydrology: flooding is eliminated over large areas and the underground water levels are stabilized. The forest vegetation varies in species diversity and structure, from young pioneer to older, mid-successional forests. The forests were classified into four associations: Salici-Populetum nigrae, Ligustro-Populetum nigrae, Fraxino-Populetum albae and Querco-Ulmetum minoris. The first three communities are ‘softwood’ because of the dominance of Salix and Populus, the fourth, dominated by Quercus robur, Fraxinus excelsior and Ulmus minor, is ‘hardwood’. Differences in structure, species composition and diversity in 10 widely varying stands in 30-yr and 150-yr old forests are quantified and interpreted in relation to the processes and gradients (moisture and texture) involved. A model of forest succession is developed as follows:

• 1 Whatever the topographic level, Salix and Populus species are the most competitive in colonizing bare sediments.
• 2 Under natural conditions, pioneer softwoods are generally replaced by hardwoods in less than 100 yr.
• 3 Old Querco-Ulmetum is basically the terminal stage of the alluvial succession.
• 4 Old softwood forests result from an interruption of the natural course of succession. Softwoods may be an intermediate or late-successional phase depending on the interruption.
• 5 Successional processes change according to hydrological and edaphic gradients.
• 6 Allogenic processes of flooding are fundamental in the space-time species pattern.
• 7 Allogenic processes are responsible for the high species and community diversity.

     

Marginal attack rate,k-values and density dependence in the analysis of contemporaneous mortality factors

1. Procedures for calculating the marginal attack rates and associated k-values from observed death rates are presented for contemporaneous predators or parasitoids that either do or do not discriminate against previously parasitized hosts.
2. The relationships among previous methods for quantifying contemporaneous mortalities are discussed.
3. Solutions to the problem of calculating marginal rates taken from human survival analysis are given under the assumption of proportional hazards. These calculations are easily extended to three or more contemporaneous sources of mortality.
4. The conditions under which proportional hazards can be expected are discussed.
5. These methods are compared to that of Varley et al., 1973 for assessment of density dependence among contemporaneous predators.

     

Species of the Genus ScrupocellariaVAN BENEDEN (Bryozoa,Anasca) from Indian Waters

Nine species of the genus Scrupocellaria VAN BENEDEN are figured and described in this paper. They are:

• 1 Scrupocellaria maderensis BUSK.
• 2 S. obtecta HASWELL.
• 3 S. mansueta WATERS.
• 4 S diadema BUSK.
• 5 S. scruposa (LINNAEUS).
• 6 S. spatulata (D'ORBIGNY).
• 7 S. delilii (AUDOUIN).
• 8 S. bertholettii (AUDOUIN).
• 9 S. talonis OSBURN.

The specimens were collected from the south west and south east coasts of India. Six species are described for the first time from Indian waters. Variations noticed in the morphology of the above species with those described elsewhere are assessed and discussed. A study of the genus from the available material shows that characters like the number of spines and nature of scuta show considerable intraspecific differences. Variation in spine number is a common occurrence and undue importance to spine number, especially in the case of tropical species, should be given with due caution. The history of S. bertholettii is really confusing especially in view of the creation of the var. tenuirostris. A comparative study of the type specimens would help to clarify the taxonomic ambiguity of this species.     

A fuzzy coding approach for the analysis of long-term ecological data

• 1 We present an unconventional procedure (fuzzy coding) to structure biological and environmental information, which uses positive scores to describe the affinity of a species for different modalities (i.e. categories) of a given variable. Fuzzy coding is essential for the synthesis of long-term ecological data because it enables analysis of diverse kinds of biological information derived from a variety of sources (e.g. samples, literature).
• 2 A fuzzy coded table can be processed by correspondence analysis. An example using aquatic beetles illustrates the properties of such a fuzzy correspondence analysis. Fuzzy coded tables were used in all articles of this issue to examine relationships between spatial-temporal habitat variability and species traits, which were obtained from a long-term study of the Upper Rhône River, France.
• 3 Fuzzy correspondence analysis can be programmed with the equations given in this paper or can be performed using ADE (Environmental Data Analysis) software that has been adapted to analyse such long-term ecological data. On Macintosh Apple^TM computers, ADE performs simple linear ordination, more recently developed methods (e.g. principal component analysis with respect to instrumental variables, canonical correspondence analysis, co-inertia analysis, local and spatial analyses), and provides a graphical display of results of these and other types of analysis (e.g. biplot, mapping, modelling curves).
• 4 ADE consists of a program library that exploits the potential of the HyperCard^TM interface. ADE in an open system, which offers the user a variety of facilities to create a specific sequence of programs. The mathematical background of ADE is supported by the algebraic model known as ‘duality diagram’.

     

A pilot analysis of gut contents in termites from the Mbalmayo Forest Reserve,Cameroon

Abstract.

• 1 Gut content analysis was carried out on eight species of higher termites representing the four included subfamilies and notional soil-feeding and wood-feeding forms. A lower termite species feeding on wood was also examined.
• 2 Pooled homogenates equivalent in volume to twenty hindguts of Thoracotermes macrothorax were diluted, stained and scored present/absent in 500 haemacytometer fields for ten content item categories: macerated organic material, lignified tissue, plant tissue fragments, fungal mycelium, arthropod parts, plant roots, safranin +ve, gentian violet +ve, humus and silica. For interspecific comparisons, the occurrence of each category was expressed as a proportion of the total haemacytometer cells examined.
• 3 A hierarchical classification of the species, based on gut contents, was prepared using a two-way indicator species analysis, and suggested the following rank order of species along a hypothetical humification gradient (soil to sound wood): Thoracotermes macrothorax, Astalotermes quietus (both soil-feeders), Termes hospes, Amalotermes phaecocephalus, Pseudacanthotermes militaris, Microtermes congoensis, Nasutitermes lujae, Microcerotermes parvus, Schedorhinotermes putorius (all notional wood-feeders). Arthropod parts, silica and humus were identified as indicator factors.
• 4 It is proposed that wood-feeding forms can be subdivided into a group consuming some silica and humus (five species: humified wood-feeders) and a second group of sound wood-feeders (two species).
• 5 Pianka's equations for diet breadth and diet overlap were also applied to the data. These identified Microtermes congoensis, Schedorhinotermes putorius and Pseudacanthotermes militaris as the most specialized feeders, i.e. that they can extract their nutrients from the least heterogenous substrates.

     

Interstitial cells of Cajal,macrophages and mast cells in the gut musculature: morphology,distribution, spatial and possible functional interactions

• ? Introduction
• ? Identification of the cells
  • ‐ ICC
  • ‐ Macrophages
    • ‐ Activation
    • ‐ Identification
  • ‐ Mast cells
    • ‐ Activation
    • ‐ Identification
• ? Cell distribution
  • ‐ ICC in rodent gastrointestinal tract
  • ‐ ICC in human gastrointestinal tract
  • ‐ Macrophages in rodent gastrointestinal tract
  • ‐ Macrophages in human gastrointestinal tract
  • ‐ Mast cells in rodent gastrointestinal tract
  • ‐ Mast cells in human gastrointestinal tract
• ? Inflammation
  • ‐ Models of inflammation
    • ‐ LPS administration
    • ‐ Surgical anastomosis
    • ‐ Ileal obstruction
    • ‐ Post‐operative ileus
    • ‐ Helminth infections
  • ‐ Inflammatory bowel disease
  • ‐ Achalasia
• ? Diabetes mellitus
  • ‐ NOD/LtJ mice
  • ‐ STZ‐DM rats
• ? Conclusions

Interstitial cells of Cajal (ICC) are recognized as pacemaker cells for gastrointestinal movement and are suggested to be mediators of neuromuscular transmission. Intestinal motility disturbances are often associated with a reduced number of ICC and/or ultrastructural damage, sometimes associated with immune cells. Macrophages and mast cells in the intestinal muscularis externa of rodents can be found in close spatial contact with ICC. Macrophages are a constant and regularly distributed cell population in the serosa and at the level of Auerbach’s plexus (AP). In human colon, ICC are in close contact with macrophages at the level of AP, suggesting functional interaction. It has therefore been proposed that ICC and macrophages interact. Macrophages and mast cells are considered to play important roles in the innate immune defence by producing pro‐inflammatory mediators during classical activation, which may in itself result in damage to the tissue. They also take part in alternative activation which is associated with anti‐inflammatory mediators, tissue remodelling and homeostasis, cancer, helminth infections and immunophenotype switch. ICC become damaged under various circumstances – surgical resection, possibly post‐operative ileus in rodents – where innate activation takes place, and in helminth infections – where alternative activation takes place. During alternative activation the muscularis macrophage can switch phenotype resulting in up‐regulation of F4/80 and the mannose receptor. In more chronic conditions such as Crohn’s disease and achalasia, ICC and mast cells develop close spatial contacts and piecemeal degranulation is possibly triggered.