Paleolimnology of Qilu Hu,Yunnan Province,China

Qilu Hu is a large (A = 36.9 km²), shallow (z_max = 6.8 m) lake that lies at an elevation of 1797 m above msl on the Yunnan Plateau, southern China. Lake waters are hard (Mg = 3.2m eq L^–1, Ca = 1.3 meq L^–1 ), fresh (conductivity = 380 S cm ^–1), and productive (Secchi < 40 cm). An 11-m sediment core has a basal ¹⁴C age of 30960 ± 860 B.P. Sediments between 11 m and 6 m are high in % dry weight, rich in clay components Al₂O₃, Fe₂O₃, K₂O, MgO, and low in organic C (6.1%), carbonate-C (<1.0%), total N (<3.2 mg g^–1), and total S (<-1.7 mg g^–1). Diatoms and pollen indicate open-water conditions between 9.0 m and 6.0 m (1342011790 B.P.). Above 6.0 m, CaCO₃ and organic matter concentrations increase relative to clastics. The transition marks a change to shallow-water conditions as inferred from diatoms and pollen, and probably reflects a shift to drier climate. Uppermost (80-0 cm) red clays were deposited rapidly, probably as a consequence of recent (decades to centuries) riparian disturbances (e.g. agriculture, lake-bottom reclamation, urban development). Dates assigned to events in the Qilu Hu profile are tentative because of potential hard-water-lake error.     

Codon usage divergence of homologous vertebrate genes and codon usage clock

Summary This paper is concerned with the divergence of synonymous codon usage and its bias in three homologous genes within vertebrate species. Genetic distances among species are described in terms of synonymous codon usage divergence and the correlation is found between the genetic distances and taxonomic distances among species under study. A codon usage clock is reported in alphaglobin and beta-globin. A method is developed to define the synonymous codon preference bias and it is observed that the bias changes considerably among species.     

Effects of acidic pH on predation rates and survivorship of damselfly nymphs

Environmental variables such as pH critically affect the physiology and ecology of aquatic organisms. Our lack of information regarding indirect effects of acid precipitation requires investigation of acid stress and response to acid stress by species of freshwater communities. Damselfly nymphs Enallagma civile (Odonata: Coenagrionidae) are abundant aquatic predators and food items for other secondary consumers.We investigated the effects of low pH on mortality, survivorship, predation rate, respiration rate, and caloric content of nymphs of E. civile. We hypothesized that acid stress would increase mortality and decrease predation rate among surviving individuals. We hypothesized that respiration rate and caloric content as measures of physiological condition would decrease in acid-stress conditions.We cultured individual early-instar nymphs in the laboratory with a controlled diet of mosquito larvae. The nymphs were reared to final instar in pond water and artificially reconstituted soft water (RSW) adjusted to pH 3.5, 4.5, 5.5, and ambient conditions of the collection site.Predation rate was significantly lower in RSW than in pond water in treatments of equivalent H⁺ concentrations. This indicated stress from differences in dissolved solids in RSW compared with pond water. Acid conditions significantly affected predation rates in pond water, but only at pH 3.5 and only for the largest instar. Mortality increased and survivorship decreased at low pH. Early-instar mortality and survivorship were particularly susceptible to acid stress. Treatments of pH 4.5, 5.5 and ambient did not significantly alter respiration rate or caloric content. However, respiration rate and caloric content increased at pH 3.5.Damselfly nymphs tolerated pHs as low as 4.5 without significant changes (including predation rate). However, the effects of pH 3.5 were significant and greatly lowered the predation and fitness of the nymphs.author for correspondence     

(A-C-B) human proinsulin, a novel insulin agonist and intermediate in the synthesis of biosynthetic human insulin.

The hormone insulin is synthesized in the beta cell of the pancreas as the precursor, proinsulin, where the carboxyl terminus of the B-chain is connected to the amino terminus of the A-chain by a connecting or C-peptide. Proinsulin is a weak insulin agonist that possesses a longer in vivo half-life than does insulin. A form of proinsulin clipped at the Arg65-Gly66 bond has been shown to be more potent than the parent molecule with protracted in vivo activity, presumably as a result of freeing the amino terminal residue of the A-chain. To generate a more active proinsulin-like molecule, we have constructed an "inverted" proinsulin molecule where the carboxyl terminus of the A-chain is connected to the amino terminus of the B-chain by the C-peptide, leaving the critical Gly1 residue free. Transformation of Escherichia coli with a plasmid coding for A-C-B human proinsulin led to the stable production of the protein. By a process of cell disruption, sulfitolysis, anion-exchange chromatography, refolding, and reversed-phase high-performance liquid chromatography, two forms of the inverted proinsulin differing at their amino termini as Gly1 and Met0-Gly1 were identified and purified to homogeneity. Both proteins were shown by a number of analytical techniques to be of the inverted sequence, with insulin-like disulfide bonding. Biological analyses by in vitro techniques revealed A-C-B human proinsulin to be intermediate in potency when compared to human insulin and proinsulin. The time to maximal lowering of blood glucose in the fasted normal rat appeared comparable to that of proinsulin. Additionally, we were able to generate fully active, native insulin from A-C-B human proinsulin by proteolytic transformation. The results of this study lend themselves to the generation of novel insulin-like peptides while providing a simplified route to the biosynthetic production of insulin.     

Susceptibility of house flies (Diptera: Muscidae) and five pupal parasitoids (Hymenoptera: Pteromalidae) to abamectin and seven commercial insecticides.

Assays of five commercial insecticides applied as residual sprays at label rates to plywood indicated the most toxic insecticide overall for pteromalid parasitoids of house flies, Musca domestica L., was Atroban (permethrin), followed by Ciodrin (crotoxyphos), Rabon (tetrachlorvinphos), Ectrin (fenvalerate), and Cygon (dimethoate). Insecticide-susceptible house flies were susceptible to all five insecticides (mortality, 62-100%). Flies that were recently colonized from populations on dairy farms in New York were susceptible only to Rabon. Urolepis rufipes (Ashmead) was the most susceptible parasitoid species overall to these insecticides, followed by Muscidifurax raptor Girault & Sanders, Nasonia vitripennis Walker, Pachycrepoideus vindemmiae (Rondani), and Spalangia cameroni Perkins. Compared with susceptible flies, newly colonized flies showed moderate resistance to avermectin B1a (abamectin). Abamectin was more toxic to all of the parasitoids except N. vitripennis and S. cameroni than to newly colonized house flies when exposed for 90 min to plywood boards treated with 0.001-0.1% abamectin. Space sprays with Vapona (dichlorvos) killed all of the parasitoids and susceptible flies and 64% of the newly colonized flies when insects were placed directly in the path of the spray; mortality was substantially lower among flies and parasitoids protected under 5 cm of wheat straw. Space sprays with Pyrenone (pyrethrins) killed greater than 86% of all insects exposed to the spray path except for the newly colonized flies (1% mortality); mortality of insects protected under straw was low (less than 12%) except for S. cameroni (76%). Because responses of the five parasitoids to the different insecticides varied considerably, general conclusions about parasitoid susceptibility to active ingredients, insecticide class, or method of application were not possible.     

The formation of cytoplasmic channels between tapetal cells inZea mays

Summary In this report we show that large cytoplasmic channels form between the tapetal cells ofZea mays (maize) during the period of tapetal cell differentiation. Tapetal cells are connected by plasmodesmata through their cellulosic cell walls prior to the first meiotic division of the meiocytes. As the tapetal cellulose wall is degraded at the onset of meiosis, both plasmodesmata and cytoplasmic channels measuring 50–200 nm are detectable between tapetal cells. By the time the meiotic tetrad is formed, the cytoplasmic channels are well-established and vary in size from 100–400 nm. The channels, with an average diameter of 200–300 nm, persist after the microspores are released from the callose wall and throughout the period of exine development in microsporogenesis. The channels could potentially allow for free exchange of cytoplasm and organelles. As the tapetal cells begin to pull apart and become vacuolate prior to microspore mitosis, the connecting channels are no longer detectable.     

A general method of polymerase-chain-reaction-enabled protein domain mutagenesis: construction of a human protein S-osteonectin gene.

Polymerase chain reaction (PCR) amplification was employed to construct a mosaic gene consisting of the propeptide region of protein S and the glutamic acid-rich domain of osteonectin. The strategy is straightforward, results in large amounts of material, and is universally applicable for the generation of protein domain chimeras. In some cases 10% dimethyl sulfoxide aided the amplification. Four base CCGC "clamp" sequences adjacent to BamHI restriction sites at the ends of the PCR products were used to enhance the ligation of products. A hybrid inverse complement oligonucleotide primer composed of sequences containing 20 nucleotides of protein S and 16 nucleotides of osteonectin was used in the first round of PCR. An additional osteonectin sequence was added to the initial amplified product by performing PCR using a second "boot-strap" primer containing 18 nucleotides of osteonectin. Primers used to amplify osteonectin encompassed the 146-aminoacid NH2-terminal half of osteonectin. The double-stranded first-round fragments of protein S-osteonectin and osteonectin were subsequently mixed together and one elongation cycle of PCR was performed. Annealing occurred as the result of the 34-base-pair overlap region composed of osteonectin sequence. Taq polymerase was used for elongation with subsequent recombinant DNA synthesis. After elongation, external primers were added to amplify the protein S-osteonectin gene construct. The protocol we have developed allows noncoding and coding segments of DNA to be linked, GC-rich areas of DNA to be amplified, hybridization temperatures to be increased, annealing times to be reduced, and PCR of products to be subcloned.     

Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis.

The reactions of Rhodopseudomonas viridis cytochrome c2 and horse cytochrome c with Rps. viridis photosynthetic reaction centers were studied by using both single- and double-flash excitation. Single-flash excitation of the reaction centers resulted in rapid photooxidation of cytochrome c-556 in the cytochrome subunit of the reaction center. The photooxidized cytochrome c-556 was subsequently reduced by electron transfer from ferrocytochrome c2 present in the solution. The rate constant for this reaction had a hyperbolic dependence on the concentration of cytochrome c2, consistent with the formation of a complex between cytochrome c2 and the reaction center. The dissociation constant of the complex was estimated to be 30 microM, and the rate of electron transfer within the 1:1 complex was 270 s-1. Double-flash experiments revealed that ferricytochrome c2 dissociated from the reaction center with a rate constant of greater than 100 s-1 and allowed another molecule of ferrocytochrome c2 to react. When both cytochrome c-556 and cytochrome c-559 were photooxidized with a double flash, the rate constant for reduction of both components was the same as that observed for cytochrome c-556 alone. The observed rate constant decreased by a factor of 14 as the ionic strength was increased from 5 mM to 1 M, indicating that electrostatic interactions contributed to binding. Molecular modeling studies revealed a possible cytochrome c2 binding site on the cytochrome subunit of the reaction center involving the negatively charged residues Glu-93, Glu-85, Glu-79, and Glu-67 which surround the heme crevice of cytochrome c-554.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mating behavior and the evolutionary significance of mate guarding in three species of crane flies (Diptera: Tipulidae)

Three species of crane flies-Dactylolabis montana, Limonia simulans,and Antocha saxicola-gather near streams to mate and oviposit. All species are polygamous and sex ratios at these sites are male-biased. After a short mating bout, males guard females by standing over them during oviposition. Sperm competition appears to be intense and to follow last-male advantage, based on the packing of sperm within the two elongate spermathecae. Males of A. saxicolasuccessfully defend against rivals over 85% of the time. In contrast, defending males of D. montanaand L. simulanslose the female over 65% of the time during interactions with rivals. Despite the high frequency of loss, defending males gain additional oviposition time by engaging rivals in combat while the female continues to oviposit. Thus, a guarding male does not have to retain the female for guarding to be adaptive. Legs and claws of all species are sexually dimorphic and play an important role in guarding and defending.     

Colorimetric determination of L-phenylacetyl carbinol produced by biotransformation of benzaldehyde and pyruvate using Saccharomyces cerevisiae

Summary The utility of a colorimetric method, based on the Voges-Proskauer reaction, for L-phenylacetyl carbinol (L-PAC) determination has been evaluated. The relative absorbances observed for equivalent concentrations of L-PAC and acetylbenzoyl at 580 nm were determined. L-PAC manifested a lower absorbance (60&#x2013;68%) than the equivalent acetylbenzoyl concentration.