A bioenergetic study of a benthic nematode,plectus palustris de man 1880, throughout its life cycle

Summary Growth and reproduction of the parthenogenetic freshwater nematode,Plectus palustris, were studied at different controlled levels of food densities at 20° C. A bacteria-sloppy agar mixture was used as substrate and food medium. No growth or reproduction occurred at the lowest food density (8.10⁷ bacterial cells ml^-1). At 8.10⁸ cells ml^-1, the larval duration was 18.5 days, the instantaneous growth rate (g) of young larvae 0.2 d^-1 and the daily fecundity rate during a prolonged period of constant egg production 12.6 eggs·d^-1. At a food density of 8.10⁹ cells ml^-1, the corresponding values are 12.5 days, 0.4 d^-1 and 37.7 eggs d^-1.By including the data on respiration from a previous paper (Klekowski et al., 1979), the energetics of the species at different food densities can be discussed: production processes are apparently more dependent on food supply than respiration. However, prolongation of the larval phase in lower food densities greatly increases the cumulated respiratory costs per unit production. A second point is the ability to produce smaller-sized primiparous females in sub-optimal food which shortens the immature life period and serves to reduce the burden of cumulated metabolic costs for attaining sexual maturity.A comparison of the range of food densities used in the experiments with bacterial densities known from lake sediments of different trophic type suggests that food is likely to be the main factor governing the population dynamics of bacterivorous species under field situations.     

Induction of nitrate reductase and membrane cytochromes in wild type and chlorate-resistant Paracoccus denitrificans

An experimental system has been devised for induction of nitrate reductase in suspensions of wild type Paracoccus denitrificans incubated with limited aeration in the presence of azide, nitrate or nitrite. Azide promoted maximum synthesis of enzyme, accompanied by formation of excess b-type cytochrome; the level of enzyme attained with nitrate was less and c-type cytochrome predominated in the membrane. The nitrate reductase was solubilized with deoxycholate from membranes of azide-induced cells and was identified as a major polypeptide M _r =150,000 by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Mutants strains lacking nitrate reductase activity were isolated on the basis of resistance to chlorate and mutant M-1 was examined in detail. When incubated in the cell suspension system M-1 formed a membrane protein M _r =150,000 similar to that attributed to nitrate reductase in the wild type. Maximum formation of the protein by M-1 occurred without inducer and it was accompanied by synthesis of excess b-type cytochrome. The observations with wild type and M-1 indicate that nitrate reductase protein and b-type cytochrome are coregulated and that the active enzyme has a role in regulating its own synthesis.Non-standard Abbreviations SDS sodium dodecyl sulphate - PAGE polyacrylamide gel electrophoresis - DOC sodlum deoxycholate     

Effects of molybdenum and tungsten on induction of nitrate reductase and formate dehydrogenase in wild type and mutant Paracoccus denitrificans

Molybdenum is required for induction of nitrate reductase and of NAD-linked formate dehydrogenase activities in suspensions of wild type Paracoccus denitrificans; tungsten prevents the development of these enzyme activities. The wild type forms a membrane protein M _r150,000 when incubated with tungsten and inducers of nitrate reductase and this is presumed to represent an inactive form of the enzyme. Suspensions of mutant M-1 did not develop nitrate reductase or formate dehydrogenase activities but the membrane protein M _r150,000 was formed under all conditions tested, including without inducers and without molybdenum. Analysis of membranes, solubilized with deoxycholate, by polyacrylamide gel electrophoresis under nondenaturing conditions showed that the mutant protein had similar electrophoretic mobility to the active nitrate reductase formed by the wilde type. Autoradiography of preparations from cells incubated with ⁵⁵Fe showed that the mutant and wild type proteins contained iron. However, in similar experiments with ⁹⁹Mo, incorporation of molybdenum into the mutant protein was not detectable.We conclude that mutant M-1 is defective in one or more steps required to process molybdenum for incorporation into molybdoenzymes. This failure affects the normal regulation of nitrate reductase protein with respect to the role of inducers.Non-Standard Abbreviations DOC deoxycholate - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate     

A portable pump sampler for lotic periphyton

A sampling technique for collecting lotic periphyton on sedimentary substrates using a peristaltic pump is described. Quantitative samples of periphyton standing crop and colonization rate are collected by the same procedure. The technique eliminates human disturbance problems associated with floating artificial samplers by establishing permanent sampling sites directly on submerged substances.     

Nitrous acid damage to duplex deoxyribonucleic acid: distinction between deamination of cytosine residues and a novel mutational lesion.

The rate of nitrous acid deamination of labeled cytosine residues in native Escherichia coli deoxyribonucleic acid was monitored in vitro by release of acid-soluble counts after treatment with uracil deoxyribonucleic acid glycosylase. The reaction exhibited a lag and was not stimulate by several agents previously shown to enhance base substitution mutagenesis during nitrous acid treatment of duplex deoxyribonucleic acid. We conclude that a significant proportion of nitrous acid induced mutagenic lesions are novel lesions and not cytosine deaminations.     

GABA induces behavioral and developmental metamorphosis in planktonic molluscan larvae

Swimming planktonic larvae of the marine gastropod mollusc Haliotis rufescens require exogenous GABA or its homologs for induction of their genetically programed behavioral and developmental metamorphosis to the adult form. This requirement is stereochemically specific and absolute; GABA at 10(-6) M is fully effective in the induction of cellular differentiation, proliferation and organogenesis. The kinetics of the development of larval competence for GABA induction, and of the early metamorphic processes induced by GABA, are described. Biochemical, histological and electron micrographic analyses suggest that cyclic AMP, calcium, and a glycopeptide secretion from the cephalic sensory complex may mediate transduction of the GABA signal in the control of behavioral and morphogenetic changes induced by this environmentally deployed transmitter substance. This first observation and characterization of a major role for GABA in the control of differentiation and development, and the experimentally tractable system in which these are demonstrated, are of significance for further biomedical research.     

Measurement of surface potential and surface charge densities of sarcoplasmic reticulum membranes

Summary The binding of the anionic fluorescent probe 1-anilino-8-naphthalene-sulfonate (ANS^–) was used to estimate the surface potential of fragmented sarcoplasmic reticulum (SR) derived from rabbit skeletal muscle. The method is based on the observation that ANS^– is an obligatory anion whose equilibrium constant for binding membranes is proportional to the electrostatic function of membrane surface potential, exp(e₀/kT, where ₀ is the membrane surface potential,e is the electronic charge, andkT has its usual meaning. The potential measured is characteristic of the ANS^– bindings of phosphatidylcholine head groups and is about one-third as large as the average surface potential predicted by the Gouy-Chapman theory. At physiological ionic strength the surface potentials, measured by ANS^–, referred to as the aqueous phase bathing the surface, were in the range –10 to –15 mV. This was observed for the outside and inside surfaces of the Ca²⁺-ATPase-rich fraction of theSR and for both surfaces of theSR fraction rich in acidic Ca²⁺ binding proteins. The inside and outside surfaces were differentiated on the basis of ANS^– binding kinetics observed in stopped-flow rapid mixing experiments. A mechanism by which changes in Ca²⁺ concentration could give rise to an electrostatic potential across the membrane and possibly result in changes in Ca²⁺ permeability.The dependence of the surface potential on the monovalent ion concentration in the medium was used together with the Gouy-Chapman theory to determine the lower limits for the surface charge density for the inside and outside surfaces of the two types ofSR. Values for the Ca²⁺-ATPase richSR fraction were between 2.9×10³ and 3.8×10³ esu/cm², (0.96×10^–6 and 1.26×10^–6 C/cm²) with no appreciable transmembrane asymmetry. A small amount of asymmetry was observed in the values for the inside and outside surfaces of the fraction rich in acidic binding proteins which were ca. 6.6×10³ and ca. 2.2×10³ esu/cm² (2.2×10^–6 and 0.73×10^–6 C/cm). The values could be accounted for by the known composition of negatively-charged phospholipids in theSR. The acidic Ca²⁺ binding proteins were shown to make at most a small contribution to the surface charge, indicating that their charge must be located at least several tens of Å from the membrane surface. The experiments gave evidence for a Donnan effect on the K⁺ distribution in the fraction rich in acidic binding proteins. This could be accounted for by the known concentration of acidic binding proteins in thisSR fraction.The equilibrium constant for ANS^– was shown to be more sensitive to changes in the divalent cation concentration than to changes in the monovalent cation concentration, as predicted by the Gouy-Chapman theory. Use of these findings together with the stopped-flow rapid mixing techniques constitutes a method for rapid and continuous monitoring of changes in ion concentrations in theSR lumen.     

Metabolic formation of nucleoside-modified analogues of S-adenosylmethionine

A Pseudo-ovalbumin gene, bearing significant nucleotide sequence homology to the ovalbumin gene, has been cloned from genomic chick DNA. Similar to the authentic ovalbumin gene, the pseudo-gene is a unique sequence gene in the chick genome and is expressed at a low level in the immature chick oviduct. In contrast to the ovalbumin gene, expression of the pseudo-gene in the oviduct is not inducible by estrogen. The concentration of pseudo-gene RNA is only ～0.01% of that of authentic ovalbumin mRNA in estrogen-stimulated oviduct cells. Nucleotide sequence analysis of the two sequence related genes may reveal the molecular basis of differential response to steroid hormone induction in the same tissue.     

Purine transport by Malpighian tubules of pteridine-deficient eye color mutants of Drosophila melanogaster

Uptakes of guanine into Malpighian tubules of wild-type Drosophila and the eye color mutants white (w), brown (bw), and pink-peach (p ^p) have been compared. Tubules for each of these mutants are unable to concentrate guanine intracellularly. The transport of xanthine and riboflavin is also deficient in w tubules. The transport of guanosine, adenine, hypoxanthine, and guanosine monophosphate is similar in wild-type and white Malpighian tubules. These data and other information about these mutants make it likely that these pteridine-deficient eye color mutants do not produce pigments because of the inability to transport a pteridine precursor. This view supports the hypothesis that mutants which lack both pteridine and ommochromes do so because precursors to both classes of pigments share a common transport system.This work was supported by Grant GM22366 from NIH.     

Response of lake phytoplankton communities to in situ manipulations of light intensity and colour

Phytoplankton preferences for light intensity and colour weredetermined in field experiments using coloured plexiglass cubessuspended at different depths in Heney Lake, Québec.Diatoms and green algae favoured intensities greater than 1%I_o (surface irradiance) contrary to dinoflagellates and otherflagellates that preferred lower intensity. Red radiation usuallyincreased the relative proportion of blue-greens, diatoms andgreen algae, whereas it reduced that of dinoflageilates. Wepropose that differential utilization of the light gradientallows certain phytoplankton taxa to partition the water column,thereby reducing potential competition. This is supported bythe general agreement between our findings and the known depthdistribution of algae in lakes.