A comparison of the toxic and sub-lethal effects of fluvalinate and esfenvalerate on the twospotted spider mite (Acari: Tetranychidae)

There was no difference in the direct toxicity of fluvalinate and esfenvalerate to twospotted spider mite (TSSM), Tetranychus urticae Koch. adults. The residual toxicity LC₅₀ of esfenvalerate was lower. Neither pyrethroid was toxic (<10% mortality) to TSSM eggs or adults at their recommended field concentrations. Fluvalinate was twice as toxic (45% mortality) than esfenvalerate to TSSM larvae at 0.01 g.a.i L^-1. The toxicity of the pyrethroids to TSSM protonymphs and deutonymphs was similar (16–28% mortality at 0.1 g a.i. L^-1). Dispersal from the treated surface was the main response to both pyrethroids by TSSM protonymphs, deutonymphs and adults. Maximum run-off by TSSM adults from fluvalinate and esfenvalerate treated surfaces was found with 0.01 and 0.005 g a.i. L^-1 respectively. Spin-down from pyrethroid treated surfaces was positively correlated with concentration. Oviposition was negatively correlated with concentration. Fluvalinate caused greater reductions in oviposition than esfenvalerate. Both pyrethroids reduced TSSM development rate from larval, protonymph and deutonymph stages, but fluvalinate caused larger reductions. Both pyrethroids prevented mating: for ten days oviposition 93% and 98% of offspring were male for esfenvalerate and fluvalinate respectively at 0.1 g a.i. L^-1. These findings are discussed with respect to the incidence of pyrethroid induced mite outbreaks.     

Evidence for a novel pathway in the degradation of fluorene by Pseudomonas sp. strain F274.

A fluorene-utilizing microorganism, identified as a species of Pseudomonas, was isolated from soil severely contaminated from creosote use and was shown to accumulate six major metabolites from fluorene in washed-cell incubations. Five of these products were identified as 9-fluorenol, 9-fluorenone, (+)-1,1a-dihydroxy-1-hydro-9-fluorenone, 8-hydroxy-3,4-benzocoumarin, and phthalic acid. This last compound was also identified in growing cultures supported by fluorene. Fluorene assimilation into cell biomass was estimated to be approximately 50%. The structures of accumulated products indicate that a previously undescribed pathway of fluorene catabolism is employed by Pseudomonas sp. strain F274. This pathway involves oxygenation of fluorene at C-9 to give 9-fluorenol, which is then dehydrogenated to the corresponding ketone, 9-fluorenone. Dioxygenase attack on 9-fluorenone adjacent to the carbonyl group gives an angular diol, 1,1a-dihydroxy-1-hydro-9-fluorenone. Identification of 8-hydroxy-3,4-benzocoumarin and phthalic acid suggests that the five-membered ring of the angular diol is opened first and that the resulting 2'-carboxy derivative of 2,3-dihydroxy-biphenyl is catabolized by reactions analogous to those of biphenyl degradation, leading to the formation of phthalic acid. Cell extracts of fluorene-grown cells possessed high levels of an enzyme characteristic of phthalate catabolism, 4,5-dihydroxyphthalate decarboxylase, together with protocatechuate 4,5-dioxygenase. On the basis of these findings, a pathway of fluorene degradation is proposed to account for its conversion to intermediary metabolites. A range of compounds with structures similar to that of fluorene was acted on by fluorene-grown cells to give products consistent with the initial reactions proposed.     

Hemoglobin affinity for 2,3-bisphosphoglycerate in solutions and intact erythrocytes: studies using pulsed-field gradient nuclear magnetic resonance and Monte Carlo simulations.

The diffusion coefficient (D) of 2,3-bisphosphoglycerate (DPG) was measured using pulsed-field gradient (PFG)-31P nuclear magnetic resonance spectroscopy in solutions containing 2.7-5.0 mM hemoglobin (Hb) and a range of DPG concentrations. The dependence of the measured values of D on the fraction of the total DPG in the sample that is bound to Hb enabled the estimation of the dissociation constants (Kd) of complexes of DPG with carbonmonoxygenated, oxygenated, and deoxygenated Hb; the values of Kd (mM), measured at 25 degrees C, pH 6.9 and in 100 mM bis Tris/50 mM KCl, were 1.98 +/- 0.26, 1.8 +/- 0.5 and 0.39 +/- 0.26, respectively. In intact erythrocytes the apparent diffusion coefficient, Dapp, of DPG was larger in oxygenated and carbonmonoxygenated cells (6.17 +/- 0.20 x 10(-11) m2s-1) than in deoxygenated cells (4.10 +/- 0.23 x 10(-11) m2s-1). Changes in intracellular DPG concentration (5-55 mM) in erythrocytes, brought about by incubation in a medium containing inosine and pyruvate, did not result in significant changes in the value of Dapp; this result supports the hypothesis that DPG binds to other sites in the erythrocyte. Monte Carlo simulations of diffusion in biconcave discs were used to test the adequacy of the values of Kd estimated in solution to describe the binding of DPG to Hb in oxygenated and deoxygenated erythrocytes. The results of the simulations implied that the value of Kd estimated for deoxygenated Hb-DPG was greater than expected from the experiments involving intact erythrocytes. This difference is surmised to be at least partly due to the difficulty of measuring D at low-ligand concentrations. Notwithstanding this shortcoming, the PFG method appears to be suitable for probing interactions between macromolecules and ligands when the Kd is in the millimolar range. It is one of the few techniques available in which these interactions can be studied in intact cells. In addition, the Monte Carlo simulations of the diffusion experiments highlighted important differences between theory and experiment relating to the nature of molecular motion inside the cells.     

Gravitropically-stimulated seedlings show autotropism in weightlessness

In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed.     

Catalytic Properties of a Newly Discovered Acyltransferase That Synthesizes N-Acylphosphatidylethanolamine in Cottonseed (Gossypium hirsutum L.) Microsomes

We recently demonstrated that cotyledons of cotton (Gossypium hirsutum L.) seedlings synthesize N-acylphosphatidylethanolamine (NAPE), an unusual acylated derivative of phosphatidylethanolamine (PE), during postgerminative growth (K.D. Chapman and T.S. Moore [1993] Arch Biochem Biophys 301: 21-33). Here, we report the discovery of an acyltransferase enzyme, fatty acid: diacylphosphatidylethanolamine N-acyltransferase (designated NAPE synthase), that synthesizes NAPE from PE and free fatty acids (FFA) in cottonseed microsomes. [14C]NAPE was synthesized from [14C]palmitic acid and endogenous PE in a time-, pH-, temperature-, and protein concentration-dependent manner. [14C]Palmitic acid was incorporated exclusively into the N-acyl position of NAPE. [14C]palmitoyl coenzyme A (CoA) and [14C]-dipalmitoyl phosphatidylcholine (PC) were poor acyl donors for the synthesis of NAPE (i.e. 200- and 3000-fold lower incorporation efficiency than palmitic acid, respectively). Synthesis of NAPE from palmitoyl-CoA and dipalmitoyl-PC was observed only after the release of FFA in microsomes. We observed a temperature optimum of 45[deg]C and a pH optimum of 8.0 for the synthesis of [14C]NAPE from [14C]palmitic acid (or from [14C]PE). NAPE synthase activity showed no apparent divalent cation requirement. Notably, activity was stimulated by HPO42-, HCO3-, SO42-, and NADPH, whereas activity was inhibited by Ca2+, Mn2+, Cd2+, ATP, ADP, flavin adenine disnucleotide, and flavin mononucleotide. Other nucleotide triphosphates (GTP and CTP) and pyridine dinucleotides (NAD, NADH, and NADP) did not appreciably affect NAPE synthase activity. Initial velocity measurements of NAPE synthase activity at increasing concentrations of palmitic acid showed non-Michaelis-Menten, biphasic kinetics. A high-affinity site (S0.5 = 7.2 [mu]M, Vmax = 18.8 nmol h-1 mg-1 of protein) and a low-affinity site (S0.5 = 32.0 [mu]M, Vmax = 44.9 nmol h-1 mg-1 of protein) were identified. Both sites exhibited positive cooperativity. Adding myristic, stearic, or oleic acids at equimolar amounts reduced the incorporation of [14C]palmitic acid into NAPE at low concentrations (10 [mu]M, high-affinity site) but not at high concentrations (50 [mu]M, low-affinity site), indicating that the two putative sites can be distinguished by their fatty acid preferences.     

Counterselection on sex chromosomes in the Mus musculus European hybrid zone

The extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 cM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between Mus musculus domesticus and M. m. musculus in Denmark. The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh1, Amy, Gpd1, Pgm1, Es1, Es2, Mpi, Np1, Es10, Sod1) and the mitochondrial DNA. The cline for DXPas2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background. The clines of the other two X-linked markers, Hprt and DXPas1, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X-linked and to a lesser extent Y-linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co-adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies.     

A model of the sodium dependence of dopamine uptake in rat striatal synaptosomes

Initial velocity of uptake of dopamine (DA) has been measured in rat striatal synaptosomes as a function of both [DA] and [Na]. Carrier mediated uptake is totally dependent on external sodium. The data were fitted to a rapid equilibrium model which has been found in previous studies to fit, with appropriate simplification, uptake data for glutamate, GABA, and choline in several brain regions under varying conditions. This model also gives a good fit to the dopamine data. The minimal best fit simplification of this model allows for DA uptake along with two sodium ions and predicts that apparent maximal velocity of uptake should increase with [Na], while the Michaelis-Menten constant should decrease. The minimal best fit model for DA, and a number of kinetic parameters which quantitate the model, are compared to those for the GABA, glutamate, and choline transporters. The results are consistent with a symmetrical, rapid equilibrium model, which has been presented previously for other neurotransmitters and precursors (18). This model offers a unifying basis for understanding the sodium and membrane potential dependence of neurotransmitter transport and the possible participation of transporters in depolarization induced release throughout the CNS.     

Biocide susceptibility and intracellular glutathione inEscherichia coli

Summary Inhibition of growth and speed of kill by biocides with different mechanisms of action was examined with respect to intracellular glutathione levels. strain deficient in intracellular glutathione was hypersusceptible to electrophilic biocides, with the exception of an isothiazolone biocide. Growth inhibition by quaternary ammonium compounds and radical-generating biocides was unaffected by intracellular glutathione levels. Speed of kill experiments demonstrated a faster rate of killing by formaldehyde in both log and stationary phase cultures of the glutathione-deficient strain as compared to its wild-type parent. Glutathione levels had no effect on the speed of kill by hydrogen peroxide in log phase cultures, but resulted in an increased rate of killing in stationary phase cultures. Stationary phase cultures of the glutathione-deficient strain were killed by a quaternary ammonium biocide at a slower than the glutathione-replete strain. These studies provide information about both the mechanism of action of biocides as well as the role of glutathione in determining microbicide susceptibility.