Microhabitat preferences of benthic fauna in a woodland stream

Estimates of numbers, biomass, and diversity of benthic macroinvertebrates were made quarterly over a two-year period to investigate microhabitat preferences. Although biomass of most taxa was significantly different among sampling times, physical factors also appeared to be important in determining abundance of many taxa. Optimum depth, velocity, substrate type, and turbulence were determined for major taxa. Optimum conditions for diversity appeared to be 34 cm depth, 60 cm s^?1 velocity, and rubble and boulder substrate type. Habitat preference functions were derived for several taxa based on significant polynomial regressions of biomass on depth, velocity, substrate, and Froude number (turbulence). The relationship between abundance and physical habitat conditions was tested by using the product of the preference factors (range: 0–1) for depth, velocity and substrate type as a measure of habitat suitability (joint preference factor). There were significant correlations between biomass [transformed by log_e (x + 1)] of 10 benthic species and the joint preference factor. The joint preference factors accounted for from 11 to 61% of the variation of biomass of the 10 benthic species. The intercepts of the relationships between biomass of individual species and the joint preference factor were not significantly different from zero for any species. Therefore, the joint preference factors appear to be valid indicators of biomass. The preference functions have utility in habitat assessment studies, specifically with regard to minimum instream flow determinations.     

Inability of diethylstilbestrol to induce 6-thioguanine-resistant mutants and to inhibit metabolic cooperation of V79 Chinese hamster cells

The mutagenicity of diethylstilbestrol (DES) in V79 Chinese hamster cells was examined under a variety of conditions. DES over a concentration range 0.01–10 μg/ml failed to induce any increase above the spontaneous frequency of 6-thioguanine-resistant V79 cells. The effect of varying the expression time after treatment in the mutation assay from 3 to 9 days was studied and DES was nonmutagenic at all time points, while N-methyl-N′-nitro-N-nitrosoguanidine was highly mutagenic with a peak response after a 5–7 day expression time. The mutagenicity of benzo[a]pyrene and DES, both of which induce morphological and neoplastic transformation of Syrian hamster embryo (SHE) cells, was tested by cocultivating V79 cells with SHE cells for possible metabolic activation of the chemicals. Neither compound was mutagenic to V79 cells in the absence of SHE cells. Benzo[a]pyrene, but not DES, was mutagenic to V79 cells cocultivated with SHE cells. These results support the observation that DES can induce cell transformation under conditions that do not result in any measurable gene mutations. Moreover, the ability of DES to enhance the recovery of 6-thioguanine-resistant mutations was studied by determining the ability of DES to inhibit metabolic cooperation of V79 cells. Unlike the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate, DES was a weak or inactive inhibitor of metabolic cooperation.     

Zonal centrifugation and flotation– fractionation of MSD mutant mouse brain

Zonal centrifuge and flotation–fractionation profile analysis of neonatal mouse brain homogenates in iso-osmotic Ficoll–sucrose density–gradients demonstrates the presence of four light density fractions. In msd neurological mutant mice with a myelin-synthesizing deficiency syndrome, the bands appear to be relatively normal until after the 10th day of postnatal brain development. With the onset of visible neurological symptoms after the 11th day, the four density bands begin to disappear from the zonal profiles and are all but absent at the time of death at about the 21st postnatal day. In normal littermates of the mutants, the bands persist with age and intensify. Although their identities remain unknown, the top three identify by their density with adult myelin and the fourth with the lighter of two adult synaptosome fractions. Mixtures of brain homogenates between mutant and normal littermates give rise to zonal and banding profiles intermediate between the separate profiles but somewhat less than their average in intensity.     

Regulation of Tyrosyl-Transfer Ribonucleic Acid Synthetase in Bacillus subtilis

Derepression of tyrosyl-transfer ribonucleic acid synthetase in Bacillus subtilis was observed in strains grown with limiting tyrosine, but not in regulatory mutants derepressed in biosynthetic enzyme synthesis.     

Serum-dependent depression of alkaline phosphatase in HeLa cells

Reduction in alkaline phosphatase activity was observed when HeLa S3 cells were grown in Puck's medium containing high concentrations of human serum. This effect was not seen with the enzyme of Chang liver 8A cells. The induction of increased alkaline phosphatase in HeLa S3 by prednisolone or by osmolality changes was not prevented by serum. The concentration of serum in the culture medium had no influence on acid phosphatase activity.     

Influence of Calcium and Magnesium on Manganese Absorption

Mutual effects between Mn, Ca, and Mg were studied during steady-state absorption experiments with excised barley roots. Calcium appeared to enhance the rate of Mn absorption; whereas, Mg had a highly depressive effect. The combination of both Ca and Mg was even more inhibitory to Mn absorption than Mg alone. Manganese had no effect on the usual negligible Ca absorption by this tissue, but effectively inhibited the absorption of Mg. Although divalent cation absorption from the Ca-Mg-Mn system was essentially nil, K absorption was greatly stimulated in the presence of these cations.These mutual effects and others reported in the literature are explained by the hypothesis that selectivity in ion absorption results from cation-induced conformational changes in the structure of the carrier molecule.     

Fine structural study of gas secretion in the physoclistous swim bladder of Fundulus heteroclitus and Gadus callarias and in the euphysoclistous swim bladder of Opsanus tau

Summary The Haldane-Koch-Scholander-Kuhn-Steen theory of salting out countercurrent multiplication effect of the rete mirabile now accounts for release of most gases in the fish swim bladder. Evidence presented here indicates that final release is by microbubbles from the secretory epithelium. There is only one specific cell type in a highly vascularized epithelium. It is characterized by complex folds in the paravascular zone and by gas forming bodies which seem to form from plentiful Golgi material. The bodies are formed with dark amorphous matrix that becomes patterned (tubular or lamellar), finally froths and then is released to the gas surface. Residual material may form myelin-like layers on the lumenal surface. Active cells are also characterized by surface villi and subsurface, parallel cisternal spaces. Gas may be formed by cells not touching the gas surface and released through intercellular spaces. There are discontinuous desmosomes (maculae adhaerentes) near the gas surface and there are no tight junctions (zonulae occludentes). Gas release as bubbles would explain Wittenbergs observations that the gases found in swim bladders have ratios more closely related to their solubility coefficients in water than to ambient partial pressures. A surfactant may be present to lower the surface tension of the microbubbles. The carrier in the cytoplasm would have to be an iron-protein (or perhaps peroxidase) compound capable of binding molecular oxygen.Supported by grant-in-aid from the national Science Foundation (GB-676) and from the USPHS (General Medical Sciences Institute, GM-06836).     

Gene-Enzyme Relationships in Histidine Biosynthesis in Bacillus subtilis

Mutants for 9 of the 10 steps in histidine biosynthesis have been isolated and identified by enzyme assay. Each locus has been mapped in relation to the aro cluster and to other histidine loci by deoxyribonucleic acid-mediated transformation. The genes which code for enzymes 3, 6, and 8 of the pathway are linked to the aro cluster. A major histidine linkage group is composed of the genes which specify enzymes 1, 2, 5, 7, and 10. The locus which codes for step 9 of the pathway is unlinked to any other identified his loci. The major histidine cluster is loosely linked to cysB and is unlinked to any of the loci concerned with aromatic amino acid biosynthesis.     

Deoxyribonucleic Acid Synthesis During Microcyst Germination in Myxococcus xanthus

Deoxyribonucleic acid (DNA) synthesis was measured during microcyst germination in Myxococcus xanthus by radioactive thymidine incorporation, autoradiography, and chemical analysis. Microcysts contained an average of 6.6 conserved units of DNA, corresponding to 3 to 4 chromosomes per cell. Correlation of the DNA content and chromosome number of microcysts indicated that the molecular weight of the nonreplicating M. xanthus chromosome is 4.9 x 10(9) daltons. DNA synthesis was initiated 3.5 to 4 hr after induction of germination. From 4 to 6 hr, the rate of synthesis was constant and the accumulation was linear. After a lag period (6 to 6.5 hr), the rate of DNA synthesis increased, reaching a second plateau at 9 hr. From 9 to 11 hr, the rate was again constant and the accumulation was linear. Cellular division during germination showed an unusual kind of synchrony. A model is presented that accounts for chromosomal replication and cell division during microcyst germination.     

Distribution of β-thalassemia trait and erythrocyte glucose-6-phosphate dehydrogenase deficiency in the Markham river valley of New Guinea

Ten villages in or near the Markham Valley, northeastern New Guinea, have provided a sample of 476 males for the ascertainment of glucose-6-phosphate dehydrogenase (G6PD) deficiency and 810 individuals of both sexes for the investigation of the β-thalassemia trait. An extreme heterogeneity was found in the prevalence of both traits when the villages were analyzed separately (from 1.5% to 18.2% demonstrating G6PD deficiency and from 0 to 22.8% evincing β-thalassemia trait). The latter result counters an earlier report from the same region that β-thalassemia trait frequencies correlated negatively with altitude and (presumably) positively with endemicity of malaria. The present findings, based on a more representative sample, do not necessarily invalidate the relationship between malaria and β-thalassemia trait suggested by earlier studies, but they do make clear that correlation in New Guinea, at least, may be complicated by random genetic drift, although other possibilities are discussed. The heterogeneous distribution of G6PD deficiency in the present study confirms similar earlier findings. The importance of sample provenience and anthropological data in the interpretation of differences in the distribution of genetically determined traits is stressed.