Seasonal Variability in Abundance and Diversity of Soil Gymnamoebae Along a Short Transect in Southeastern USA

The abundance and diversity of gymnamoebae in three subsoils varying in compaction and water retention along a 1.2 m transect were documented as the local climatic conditions changed from late summer 1999 through mid-summer 2000. The mean density of gymnamoebae for the loose soil (1,655/g) was greater than either the most compact (1,468/g) or moderately compact soil (851/g). Minimum densities occurred in middle and late summer for all soils while significant (F = 38.803, < or = 0.0002) density peaks at 3.212/g occurred in early summer in the most compact soil, 2.928/g in the least compact, and 2,209/g in the moderately compact soil. Limax non-eruptive gymnamoebae (mt 2) correlated (r = 0.49, p < or = 0.016) with moisture while eruptive limax gymnamoebae ( 3) correlated with temperature (r = 0.07, p < or = 0.024), moisture (r = 0.58, p < or = 0.001) and precipitation (r = 0.46, p < or = 0.029). Flattened or discoid amoebae (mt 4) dominated throughout most of the survey, and the two limax groups showed inverse relationships. Chi-square analyses showed significant differences in the numbers of limax eruptive gymnamoebae compared to all other morphotypes on all but one sampling period.     

Water Flow Through Vessel Perforation Plates--A Fluid Mechanical Approach

The effect of scalariform perforation plates on the flow ofwater through plant vessels remains poorly understood. In thisstudy, a new computational tool based on finite element methodsolutions to the Navier-Stokes equation was applied to modellingfluid flow through these structures in plant vessels. Modelsdeveloped for Liriodendron tulipifera vessel elements were solvedfor cells with and without the perforation plate to study effectsof the plate on the pressure drop along the cell. Results indicatethat the pressure gradient was 5-fold greater through the platethan for regions before and after the plate. However, the perforationplate in this species accounts for only about 8% of the resistanceto flow through typical vessels because the plate influencesflow for only a short distance along the cell relative to itslength. Details of the flow characteristics through pores ofthe perforation plate are also described. Key words: Conductance, finite element method, perforation plate, vessel, water flow     

Physiological Adaptations in the Gastrointestinal Tract of Crayfish

SYNOPSIS. Crayfish are the dominant macrocrustacean in manyaquatic ecosystems and are the largest crustacean aquaculturalindustry in the United States, yet we know relatively littleabout their preferred and nutritionally important foods, aswell as their ability to utilize those foods. This review focuseson the ability of crayfish to detect foods, reduce food particlesize, digest macronutrients and the control of those functions.Of particular interest are the enzymatic capabilities of crayfish,especially trypsin, an alkaline protease, cellulase, muramidase,and possibly chitinase and chitobiase. The coordinated neuralcontrol of crayfish food location, ingestion and movement hasbeen well documented, while hormonal control mechanisms havenot. The conclusion we must draw from our current state of knowledgeis that crayfish have ample abilities to taste and locate potentialfoods and enzymatic adaptations developed in crayfish that allowuse of many of the foods they encounter in a benthic aquaticenvironment; other adaptations are lacking or have not beenelucidated.     

A calcium-binding sialoglycoprotein associated with an apparent eggshell membrane of Globodera rostochiensis

Energy dispersive X-ray microanalysis has been used to study the binding of two inhibitors of hatching in Globodera rostochiensis, ruthenium red and lanthanum, to a calcium binding site on the eggshell. Eggs were treated with either buffered ruthenium red or buffer only, and the levels of ruthenium and calcium that could be detected from the surface of eggshells were measured before and after repeated etching in a plasma oven. Counts for ruthenium increased during etching to a maximum after 8–12 min, just before the eggshell was eroded from the juvenile. The calcium levels on eggshells binding ruthenium red were suppressed relative to those from buffer. Similar experiments with lanthanum showed a significant increase in this inhibitor after 10 min etching and an accompanying suppression of calcium levels. The nature of the binding site was probed by measuring ruthenium red binding after pretreatment with selected enzymes. A non-specific protease, pronase, reduced the subsequent binding of this inhibitor but the site was resistant to trypsin in the presence of calcium. Neuraminidase also had an effect suggesting that the protein is a sialoglycoprotein. Phospholipase A2 but not Phospholipase C influenced the subsequent binding of ruthenium red. Phospholipase A₂ caused a loss of hatching ability and the degradation of a phospholipid from the eggshell. Ruthenium red binding was also reduced by treatment of eggshells with detergents or sonication. Apparently a calcium-binding sialoglycoprotein forms part of the integral proteins of an eggshell membrane located on the inner surface of the eggshell.     

THE STANDARDIZATION OF AIR-FLOW IN INSECT SUCTION TRAPS

The air-flow and its variations in sixteen insect suction traps of five different types have been measured, using regularity of air sample size as the criterion of efficiency. Traps with the air-filtering cone enclosed in a cylinder and using axial flow fans with single-phase capacitor-start-and-run or three-phase motors are most efficient and can have normal working limits of + 4 % of the mean air delivery.
However, for smaller traps which are to be used only close to the ground or in cover, the original type with exposed cone and shaded-pole motor is quite satisfactory provided certain precautions are taken. Normal working limits of 5 8 % are then obtained.
These errors are derived in detail and the expected errors in more extreme conditions and with other traps are indicated.     

Studies on plant growth-regulating substances

3-(3,5-Dichlorophenoxy)butyric acid and 2-(3,5-dichlorophenoxy)ethylamine were both shown to exert pronounced dwarfing effects on tomato seedlings. Examination of extracts of the treated plants revealed the conversion of these compounds to 3,5-dichlorophenoxyacetic acid (3,5-D) and it is concluded that the physiological activity shown in each case depends on such a conversion to 3,5-D within the tissues.     

Genic microsatellite markers derived from EST sequences of switchgrass (Panicum virgatum L.)

Switchgrass is a large, North American, perennial grass that is being evaluated as a potential energy crop. There is a need to assess genetic diversity in stored accessions and in remaining native stands to assist breeding and conservation efforts. Marker development will also be necessary for genetic linkage mapping. Toward this end, 32 switchgrass genic di‐, tri‐ and tetranucleotide repeat microsatellites were identified from expressed sequence tags (ESTs). These microsatellites were used to screen individuals from two different named cultivars. The markers displayed a high level of polymorphism consistent with the tetraploid, allogamous behaviour of the cultivars tested.