Behavioural response of Kootenai white sturgeon (Acipenser transmontanus,Richardson, 1836) early life stages to gravel,pebble, and rubble substrates: guidelines for rearing substrate size

Guidelines for creating rearing substrate for sturgeon early life stages are needed for restoration programmes creating habitats for spawning and rearing of early life stages. To determine the effects of rock size on motile early life stages, experiments were conducted in artificial streams to observe the behaviour of free embryos and larvae of Kootenai River white sturgeon (Acipenser transmontanus) relative to rock size. Most (≥90%) of the free embryos in replicate test streams with 100% gravel, 100% pebble, or 100% rubble hid under rocks, with few moving downstream. There was no difference in downstream movement of free embryos among rock treatments, therefore all rock types provided cover habitat. Similarly, in rock mixture tests, with a variable percentage of pebble, small rubble, or large rubble in different tanks, even fewer free embryos moved downstream. With increasing age, larvae increasingly used the open bottom and velocity refuges downstream of or alongside rocks of any size while drift feeding. Downstream movement of larvae in both rock regime tests was affected by rock size, with significantly reduced movement relative to increasing abundance of large rock (rubble). However, in all rock mixtures, free embryos (and later, larvae when they stopped dispersing) preferred the smallest rock size available (pebble; P = 0.0001). This suggests a strong innate preference of both life stages for small substrate that is likely related to increased survival. A rock mixture of 10% gravel (16–32 mm diameter) and 30–40% pebble (diameter, 30–60 mm) should provide adequate rearing substrate for free embryos and early‐larvae. The remaining 50–60% should be mixed rubble and boulders for spawning and egg rearing.     

碎石覆盖对河流硬质护坡土壤抗侵蚀性及植物生长的影响

针对河流硬质护坡生态修复中的稳定性和水分平衡等技术难点,提出了一种碎石覆盖技术,并通过抗冲刷实验和盆栽实验分析了不同碎石覆盖对土壤抗冲刷能力、保水性能及植物生长的影响.结果表明：粒径为1.5～2 cm的碎石覆盖处理在增强土壤抗冲刷能力、提高土壤保水性能和植物生物量方面效果明显,但覆盖厚度为5 cm和8 cm的碎石覆盖处理在抗冲刷、保水和促进植物生长方面的作用均无明显差异.厚5 cm、粒径为1.5～2 cm的碎石覆盖技术是硬质护坡生态修复中一种经济有效的技术方法.     

Extrapolative Capability of Two Models That Estimating Soil Water Retention Curve between Saturation and Oven Dryness

Accurate estimation of soil water retention curve (SWRC) at the dry region is required to describe the relation between soil water content and matric suction from saturation to oven dryness. In this study, the extrapolative capability of two models for predicting the complete SWRC from limited ranges of soil water retention data was evaluated. When the model parameters were obtained from SWRC data in the 0–1500 kPa range, the FX model (Fredlund and Xing, 1994) estimations agreed well with measurements from saturation to oven dryness with RMSEs less than 0.01. The GG model (Groenevelt and Grant, 2004) produced larger errors at the dry region, with significantly larger RMSEs and MEs than the FX model. Further evaluations indicated that when SWRC measurements in the 0–100 kPa suction range was applied for model establishment, the FX model was capable of producing acceptable SWRCs across the entire water content range. For a higher accuracy, the FX model requires soil water retention data at least in the 0- to 300-kPa range to extend the SWRC to oven dryness. Comparing with the Khlosi et al. (2006) model, which requires measurements in the 0–500 kPa range to reproduce the complete SWRCs, the FX model has the advantage of requiring less SWRC measurements. Thus the FX modeling approach has the potential to eliminate the processes for measuring soil water retention in the dry range.     

Effect of rock fragments on the percolation and evaporation of forest soil in Liupan Mountains, China

The water-retaining capacity, percolation and evaporation of stony soil in Liupan Mountains, China, were measured in order to understand the effect of rock fragments on soil hydrological processes. The results indicated that the effective water-retaining capacity of soil is positively related with the volumetric content of rock fragments, but there is no relation between saturated water-retaining capacity and rock fragment content. For the soil layers within 0–40 cm, the steady infiltration rate increases with increasing volumetric content of rock fragments until it reaches the range of 15%–20%, and then it decreases when the rock fragment content further increases. For the soil layers below 40 cm, the steady infiltration rate always increases with increasing rock fragment content. The soil evaporation rate decreases with increasing volumetric content of rock fragments when it varies in the range of 0–20%, while the soil evaporation rate keeps basically stable when the rock fragment content is higher than 20%. The soil evaporation rate shows a rising tendency with increasing size of rock fragments.     

六盘山森林土壤中的砾石对渗透性和蒸发的影响

为了解山地土壤中的砾石对土壤水文循环的影响,测定了砾石土壤的贮水能力、渗透速率和蒸发速率。结果表明,砾石含量与土壤有效贮水量呈正相关关系,但与土壤最大贮水量无明显相关。在0-40cm土层,当砾石体积含量小于15％～20％时,稳渗速率随砾石含量增加而增大,当砾石体积含量大于15％-20％时,土壤稳渗速率随砾石含量增加而减小;在40cm以下土层,稳渗速率随砾石含量增加而提高。在土壤砾石含量为0～20％时,土壤蒸发速率随砾石含量增加而降低,但在砾石含量超过20％时,土壤蒸发速率基本保持稳定。土壤蒸发速率随砾石粒径增大有升高的趋势。     

Modelling the occurrence and abundance of a colonial species,the arctic tern Sterna paradisaea in the archipelago of SW Finland

Knowledge of the habitat requirements and suitable breeding areas of sea birds is crucial for their management and conservation. However, there are still few studies that have modelled the breeding distribution and abundance of colonial sea birds. In this study, we created predictive distribution models for a colonial species, the arctic tern Sterna paradisaea, using 14 environmental variables calculated for 525 islands in the Archipelago Sea in SW Finland. We modelled the occurrence (presence‐absence) using generalised additive models (GAMs) and abundance (pair numbers/colony size) using hurdle models fitted with GAM. We tested for spatial autocorrelation in model residuals and evaluated the models on independent data. Critical factors influencing the occurrence of the arctic tern were the proportions of boulder or gravel and forest of island area, as well as island maximum elevation and area, such that the species seemed to prefer large and low islands with sparse vegetation. Abundance was influenced by the proportions of boulder or gravel and bare rock of island area, as well as exposure and island area. To some extent, different factors influenced the occurrence and the abundance. The evaluation results of the models were good, with an AUC value of 0.91 for the most accurate presence‐absence model and a Pearson's correlation coefficient of 0.60 for the most accurate hurdle model. The predictive ability of the models increased when we removed islands with single or few breeding pairs from the data set. Although the hurdle models did not produce accurate pair number estimates, they indicated which islands are suitable for larger colonies. Abundance is a crucial factor for colonial species. This modelling technique can therefore be of great value for the conservation and management of the arctic tern and similar colonial species.     

Lead Retention by Soils at Field Moisture Contents

The majority of studies pertaining to lead retention by clays and soils have examined the mechanisms, kinetics, and adsorption isotherms using the batch experiment technique that employs solid: water extracts of 1:10 and 1:20. Field soil deposits generally have much lower gravimetric water content ranging between 9 and 45%. Given the wide disparity in the solids: water ratio employed in the batch experiment technique and that prevailing in field deposits, this paper examines the lead retention characteristics of soils at field moisture contents (6%, 13%, and 25%) using artificially lead-contaminated soil specimens. A residually derived (i.e., formed by in-situ weathering of parent rock) red soil was used to prepare the artificially contaminated soil specimens. The impact of variations in clay content on lead retention was examined by diluting the residual soil with various amounts (0 to 60%) of river sand. Soil specimens remolded at 6 and 13% moisture contents produced very stiff to hard soils on compaction, while specimens remolded at 25% moisture content existed in the slurry state. The soil specimens were contaminated with low (30 mg/kg) to high (2500 mg/kg) concentrations of lead ions by remolding them with 160 ppm to 10,000 ppm ionic lead solutions. Lead retention by soils at field moisture contents was determined by extracting the lead from the soil using a water leach test. Experimental results showed that the bulk (71 to 99%) of the added lead was retained by the soil in insoluble form at the field moisture content. Correlations between the amount of lead retained and soil/solution parameters indicated that the amounts of Pb retained at field moisture content is a function of the initial Pb addition, total sand content, effective clay porosity, and soil pH.     

Root effects on soil water and hydraulic properties

Plants can affect soil moisture and the soil hydraulic properties both directly by root water uptake and indirectly by modifying the soil structure. Furthermore, water in plant roots is mostly neglected when studying soil hydraulic properties. In this contribution, we analyze effects of the moisture content inside roots as compared to bulk soil moisture contents and speculate on implications of non-capillary-bound root water for determination of soil moisture and calibration of soil hydraulic properties. In a field crop of maize (Zea mays) of 75 cm row spacing, we sampled the total soil volumes of 0.7 m × 0.4 m and 0.3 m deep plots at the time of tasseling. For each of the 84 soil cubes of 10 cm edge length, root mass and length as well as moisture content and soil bulk density were determined. Roots were separated in 3 size classes for which a mean root porosity of 0.82 was obtained from the relation between root dry mass density and root bulk density using pycnometers. The spatially distributed fractions of root water contents were compared with those of the water in capillary pores of the soil matrix. Water inside roots was mostly below 2–5% of total soil water content; however, locally near the plant rows it was up to 20%. The results suggest that soil moisture in roots should be separately considered. Upon drying, the relation between the soil and root water may change towards water remaining in roots. Relations depend especially on soil water retention properties, growth stages, and root distributions. Gravimetric soil water content measurement could be misleading and TDR probes providing an integrated signal are difficult to interpret. Root effects should be more intensively studied for improved field soil water balance calculations. Presented at the International Conference on Bioclimatology and Natural Hazards, Pol’ana nad Detvou, Slovakia, 17–20 September 2007.     

Separation of large DNA restriction fragments on a size-exclusion column by a nonideal mechanism

Double-strand DNA (dsDNA) restriction fragments were chromatographed on the DuPont Bioseries GF-250 column. Two anomolous chromatographic properties were observed. (1) A triphasic dependence of retention on dsDNA chain length was observed. Small DNA fragments (less than 500 base pairs) displayed typical size exclusion, intermediate size DNA (800-5000 base pairs) eluted in the void volume, and larger DNA fragments were increasingly retained. (2) The void volume for nucleic acids was less than that for large polypeptides. The retention of moderately large DNA fragments increased linearly as the square root of the chain length over the range 5.5 to 50 kilobase pairs (ca. 3-30 X 10(6) Mr). A number of eluant manipulations were carried out in order to examine the mechanism by which the larger DNA fragments were being retained and separated. Evidence was not obtained to support either ion exchange or reverse phase as the retention mechanism. The usefulness of such a column for molecular biological manipulations is illustrated by the rapid isolation of homogeneous viral DNA fragments resected from their cloning vectors with restriction endonucleases.     

Amino acid sequencing by gas chromatography-mass spectrometry using trifluoro-dideuteroalkylated peptide derivatives: C. The primary structure of the carboxypeptidase inhibitor from potatoes

The carboxypeptidase inhibitor from potatoes has been used to demonstrate the utility of gas chromatography-mass spectrometry for the determination of the primary structure of such large polypeptides. Two mixtures of oligopeptide fragments, obtained by limited acid hydrolysis and enzymatic digestion of this polypeptide, were transformed into the corresponding mixtures of O-trimethyl-silylated trifluoro-dideuteroethyl polyamino alcohols which were then analyzed by gas chromatography-mass spectrometry. The resulting mass spectral and retention index data allowed the identification of 61 oligopeptide fragments which were assembled by the computer by positioning all 39 amino acid residues in a unique sequence (with the exception of the assignment of the primary amide groups of Asn and Gln).     

Intrinsic curvature in the VP1 gene of SV40: comparison of solution and gel results

DNA restriction fragments that are stably curved are usually identified by polyacrylamide gel electrophoresis because curved fragments migrate more slowly than normal fragments containing the same number of basepairs. In free solution, curved DNA molecules can be identified by transient electric birefringence (TEB) because they exhibit rotational relaxation times that are faster than those of normal fragments of the same size. In this article, the results observed in free solution and in polyacrylamide gels are compared for a highly curved 199-basepair (bp) restriction fragment taken from the VP1 gene in Simian Virus 40 (SV40) and various sequence mutants and insertion derivatives. The TEB method of overlapping fragments was used to show that the 199-bp fragment has an apparent bend angle of 46 +/- 2 degrees centered at sequence position 1922 +/- 2 bp. Four unphased A- and T-tracts and a mixed A3T4-tract occur within a span of approximately 60 bp surrounding the apparent bend center; for brevity, this 60-bp sequence element is called a curvature module. Modifying any of the A- or T-tracts in the curvature module by site-directed mutagenesis decreases the curvature of the fragment; replacing all five A- and T-tracts by random-sequence DNA causes the 199-bp mutant to adopt a normal conformation, with normal electrophoretic mobilities and birefringence relaxation times. Hence, stable curvature in this region of the VP1 gene is due to the five unphased A- and T- tracts surrounding the apparent bend center. Discordant solution and gel results are observed when long inverted repeats are inserted within the curvature module. These insertion derivatives migrate anomalously slowly in polyacrylamide gels but have normal, highly flexible conformations in free solution. Discordant solution and gel results are not observed if the insert does not contain a long inverted repeat or if the long inverted repeat is added to the 199-bp fragment outside the curvature module. The results suggest that long inverted repeats can form hairpins or cruciforms when they are located within a region of the helix backbone that is intrinsically curved, leading to large mobility anomalies in polyacrylamide gels. Hairpin/cruciform formation is not observed in free solution, presumably because of rapid conformational exchange. Hence, DNA restriction fragments that migrate anomalously slowly in polyacrylamide gels are not necessarily stably curved in free solution.     

微生境对耐旱石生毛尖紫萼藓水分保持与散失特性的影响

毛尖紫萼藓(Grimmia pilifera)是典型石生耐旱藓类,水分是其生存繁衍的关键影响因素。为探究微生境对毛尖紫萼藓水分生理的影响,在安徽省大龙山国家森林公园低山丘陵区选择3种典型微生境(竹林遮蔽S-1,向阳裸岩E,薜荔灌丛遮蔽S-2),对比研究毛尖紫萼藓个体大小、饱和含水量及脱水过程中的含水量指标在不同微生境间的差异性,综合判断微生境对苔藓水分胁迫耐受性的影响及其权衡特征。结果表明:3种微生境毛尖紫萼藓个体大小及饱和含水量差异显著,其中竹林遮蔽生境毛尖紫萼藓具有较小的个体但拥有较高的内、外含水量。向阳裸岩和薜荔灌丛遮蔽生境植株大小及外吸水量接近,但前者内含水量更高。两荫蔽生境苔藓外吸水量是内吸水量的7倍,显著高于向阳裸岩生境的5.8倍。脱水过程中相同时间点向阳裸岩生境苔藓各含水量指标均高于两遮蔽生境,且达到相同含水量的时间差也随脱水进程持续而逐渐增大,这为向阳裸岩生境苔藓的有效光合作用(即相对含水量不低于35%时)及脱水后期的生理和结构调整赢得更多时间。综合而言,向阳裸岩生境毛尖紫萼藓比荫蔽生境具有更强的脱水耐受性,但后者可以通过增加外部吸水量来弥补失水过快的缺陷,这可能是不同微生境毛尖紫萼藓对水分吸收和保持的权衡策略。     

Composition and distribution of ground-dwelling beetles among oak fragments and surrounding pine plantations in a temperate forest of North China

In this study, we compared ground-dwelling beetle assemblages （Coleoptera） from a range of different oak fragments and surrounding conifer plantations to evaluate effects of forest size and surrounding matrix habitat in a temperate forest of north China. During 2000, beetles were sampled via pitfall traps within two large oak fragments （ca. 2.0-4.0 ha）, two small oak fragments （ca. 0.2-0.4 ha） and two surrounding matrices dom- inated by pine plantations （〉4 ha） in two sites of different aspects. Overall, no significantly negative effects from forest patch size and the surrounding matrix habitat were detected in total species number and abundance of ground-dwelling beetles. However, compared with small oak patches or pine plantations, more species were associated with an affinity for at least one large oak patch of the two aspects. Multivariate regression trees showed that the habitat type better determined the beetle assemblage structure than patch size and aspect, indicating a strong impact of the surrounding matrix. Linear mixed models indicated that species richness and abundance of all ground-dwelling beetles or beetle families showed different responses to the selected environmental variables. Our results suggest that more disturbed sites are significantly poorer in oak forest specialists, which are usually more abundant in large oak fragments and decrease in abundance or disappear in small fragments and surrounding matrix habitats. Thus, it is necessary to preserve a minimum size of forest patch to create conditions characteristic for forest interior, rather than the more difficult task of increasing habitat connectivity.     

Determination of thermal properties of composting bulking materials

Thermal properties of compost bulking materials affect temperature and biodegradation during the composting process. Well determined thermal properties of compost feedstocks will therefore contribute to practical thermodynamic approaches. Thermal conductivity, thermal diffusivity, and volumetric heat capacity of 12 compost bulking materials were determined in this study. Thermal properties were determined at varying bulk densities (1, 1.3, 1.7, 2.5, and 5 times uncompacted bulk density), particle sizes (ground and bulk), and water contents (0, 20, 50, 80% of water holding capacity and saturated condition). For the water content at 80% of water holding capacity, saw dust, soil compost blend, beef manure, and turkey litter showed the highest thermal conductivity (K) and volumetric heat capacity (C) (K: 0.12–0.81 W/m °C and C: 1.36–4.08 MJ/m³ °C). Silage showed medium values at the same water content (K: 0.09–0.47 W/m °C and C: 0.93–3.09 MJ/m³ °C). Wheat straw, oat straw, soybean straw, cornstalks, alfalfa hay, and wood shavings produced the lowest K and C values (K: 0.03–0.30 W/m °C and C: 0.26–3.45 MJ/m³ °C). Thermal conductivity and volumetric heat capacity showed a linear relationship with moisture content and bulk density, while thermal diffusivity showed a nonlinear relationship. Since the water, air, and solid materials have their own specific thermal property values, thermal properties of compost bulking materials vary with the rate of those three components by changing water content, bulk density, and particle size. The degree of saturation was used to represent the interaction between volumes of water, air, and solids under the various combinations of moisture content, bulk density, and particle size. The first order regression models developed in this paper represent the relationship between degree of saturation and volumetric heat capacity (r = 0.95–0.99) and thermal conductivity (r = 0.84–0.99) well. Improved knowledge of the thermal properties of compost bulking materials can contribute to improved thermodynamic modeling and heat management of composting processes.     

Colonization of artificial substrates by stream insects: Influence of substrate size and diversity

A field experiment was performed in a New Mexico (U.S.A.) stream to investigate the relation between size and diversity of substrate and numbers and diversity of colonizing insects. Baskets with either small gravel, large gravel, or a 1 : 1 mixture of the two sizes were placed in a riffle area and colonization was monitored for 19 days.Colonization was rapid, and both total number of individuals and number of species colonizing the substrates had stopped increasing by the end of the experiment. Fewer individuals colonized baskets downstream, suggesting that the drift is a major source of insect colonists. Small substrate supported more individuals and more species than the larger stones. Total number of individuals and the number of species on the mixed substrate were between numbers on small and large substrate. These results do not support previous generalizations on the relation between substrate size and complexity and the structure of invertebrate communities in streams. Results of the study are compared with the findings of recent experimental studies and it is suggested that earlier generalizations on the role of substrate size and complexity need to be reexamined.Order of authors was determined by the flip of a coin. Reprint requests may be sent to either author.     

Response of the microflora in outdoor experimental streams to pentachlorophenol: compartmental contributions.

Outdoor artificial streams were treated continuously with pentachlorophenol (PCP) for 88 days during the summer of 1983. The contributions of different stream compartments (microbial habitats) to microbial degradation of PCP were determined in a stream treated with 144 micrograms of PCP per liter. The 488-m long stream was composed of mud-bottomed pools alternating with gravel riffles. PCP loss in the stream attributable to microbial degradation after an adaptation period was in the range of 55 to 74%. Contributions to PCP loss were determined for rock surface (epilithic), macrophyte surface (epiphytic), sedimentary, and water column communities by measuring rates of PCP disappearance in stream water, containing ambient concentrations of PCP, in contact with representative compartmental samples. The specific capability, in units of micrograms of PCP per hour per square meter of stream cross-sectional area (macrophytes at maximum plant density, water column at mean depth, upper 10-cm layer of gravel), followed the order rock surface much greater than macrophytes greater than sediment approximately equal to water column. The compartmental contribution to total stream losses in units of grams per hour followed the same order, although the differences were smaller. The rate of PCP disappearance in the water column above sediment cores followed the order oxygen-rich greater than oxygen-poor approximately equal to anaerobic greater than sorption-only conditions. The large difference in specific capability between the rock surface and sediment compartments could be attributed to oxygen deficiency (because of chemical and biological oxygen demand) in the sediments. Free-floating and particle-attached organisms in the water column were important to PCP biodegradation.     

Accessibility of the ribosomal genes to micrococcal nuclease in Physarum polycephalum.

In Physarum polycephalum most genes coding for ribosomal RNA are not integrated in chromosomes, but are located in many copies in the nucleolus as plasmid-like palindromic DNA molecules. To find out whether coding sequences of rDNA are organized in a chromatin-like structure similar to that of bulk chromatin, nuclei were treated with micrococcal nuclease and DNA fragments were isolated. From bulk chromatin multimers of a basic unit of 170-180 base pairs were obtained. Nuclease fragmented DNA hybridized with labelled 19-S + 26-S rRNA was found to give the same saturation value as did unfragmented control DNA. No preferential degradation of ribosomal genes to acid soluble products was observed. A more detailed analysis of the nuclease degradation products was carried out with fragments separated by preparative gel electrophoresis. DNA eluted from the gels was hybridized in solution with labelled 19-S + 26-S rRNA. The coding sequences of rRNA were found to be degraded to approximately nucleosome size slightly more quickly than was the DNA of bulk chromatin. However, the distribution of the rDNA fragments on the gels did not coincide with the distribution of the fragments derived from bulk chromatin nucleosomes and their oligomers. The amount of rDNA in the interband regions was about intermediate between that found in the two adjacent bands. These results lead to the conclusion that the ribosomal genes, most of which are presumably active during rapid growth, are protected by proteins, probably histones. However, the ribosomal genes are present in a structure differing in some way from that of bulk chromatin.     

Response of the microflora in outdoor experimental streams to pentachlorophenol: compartmental contributions

Outdoor artificial streams were treated continuously with pentachlorophenol (PCP) for 88 days during the summer of 1983. The contributions of different stream compartments (microbial habitats) to microbial degradation of PCP were determined in a stream treated with 144 micrograms of PCP per liter. The 488-m long stream was composed of mud-bottomed pools alternating with gravel riffles. PCP loss in the stream attributable to microbial degradation after an adaptation period was in the range of 55 to 74%. Contributions to PCP loss were determined for rock surface (epilithic), macrophyte surface (epiphytic), sedimentary, and water column communities by measuring rates of PCP disappearance in stream water, containing ambient concentrations of PCP, in contact with representative compartmental samples. The specific capability, in units of micrograms of PCP per hour per square meter of stream cross-sectional area (macrophytes at maximum plant density, water column at mean depth, upper 10-cm layer of gravel), followed the order rock surface much greater than macrophytes greater than sediment approximately equal to water column. The compartmental contribution to total stream losses in units of grams per hour followed the same order, although the differences were smaller. The rate of PCP disappearance in the water column above sediment cores followed the order oxygen-rich greater than oxygen-poor approximately equal to anaerobic greater than sorption-only conditions. The large difference in specific capability between the rock surface and sediment compartments could be attributed to oxygen deficiency (because of chemical and biological oxygen demand) in the sediments. Free-floating and particle-attached organisms in the water column were important to PCP biodegradation.     

Acknowledgment

In a water wet porous medium, the antecedent moisture content controls the entrapment of LNAPL at low capillary numbers. A two‐phase retention cell study of entrapment was conducted for LNAPL water systems in a carbonate sand. For two different LNAPL water systems, it was found that a linear expression related the residual LNAPL saturation to the antecedent water saturation. The prediction of trapped LNAPL saturation compares favorably to long‐column test data obtained for the same sand. A trapping model was developed, and its predictions were compared to field measurements of trapped LNAPL saturation. Deviations between predicted and measured LNAPL saturations arose when there was a change in the median pore size distribution. In addition, a series of three‐phase (air‐LNAPL‐water) retention cell tests measured the amount of LNAPL that became trapped when the water phase was maintained at a constant saturation during LNAPL withdrawal under a negative pressure head. Under these conditions, the amount of trapped LNAPL was higher than that measured by two‐phase tests at the same water saturation.     

Quantitative analysis of the behavior of Dictyostelium discoideum amoebae: stringency of pteridine reception.

A convenient, sensitive, quantitative assay for the measurement of chemotaxis of populations of D. discoideum vegetative amoebae is presented. A strategy for determining the boundary of the bulk of a population of migrating amoebae was devised and is described. This assay employs a dynamic gradient and is independent of deaminase activity. Measurements of chemoattractant capabilities of various pteridines, folates, and mixtures of folate fragments are reported. 2-Amino 4-quinazolinone, a pterin analog without the pyrazine ring nitrogens, is chemotactic. Lumazine, deaminated pterin, inhibits chemotaxis towards pterin but not towards folic acid. Deaminofolic acid is a chemoattractant as are mixtures of lumazine plus aminobenzoylglutamic acid or deaminopteroic acid plus various amino acids. Separately, the components of these mixtures exhibit no ability to stimulate chemotaxis. These mixtures are of fragments that together comprise most of the folate structure. Our results are in accord with separate receptors for pterin vs. folic acid and with a high stringency for pterin reception but a relative tolerance for folate reception. The possibility of using such mixtures to investigate the requirements of various parts of the folate structure for competent signalling is discussed.