Rearing Boll Weevils on an Artificial Diet.

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Arsenate and Arsenite Retention and Release in Oxide and Sulfide Dominated Systems

Metal pollution of surface water resources in Texas is a significant problem, and is caused by the inflow of sediments from oil fields, old mines and industrial sites, and by the discharge of metal contaminated sewage and industrial effluents. In the preliminary phases of this project we were interested in a range of contaminant metals; however, following early experiments it was determined that emphasis would be given to arsenic due to the importance of several arsenic contaminated sites in east and central Texas. Three important general field and laboratory observations have been made concerning arsenic and have served as a basis for these studies: (1) correlations between metal concentrations of suspended solids or sediments (as measured by the recommended EPA and USGS methods) and metal levels in fish are often poor, (2) metal concentrations in pore waters of bottom sediments are often highly variable (with time and space) and often considerably higher (but sometimes lower) than in the overlying water column, (3) arsenic speciation and solubility are strongly influenced by redox potential. Existing EPA and USGS methods for quantifying the arsenic level of sediment or suspended solids primarily involve digestion by strong acids. While these methods do provide an indication of total concentration of metals, they often do not provide a reliable measure of bioavailability, either directly to aqueous animals or indirectly through the food chain. Inorganic arsenic exists primarily in the +3 or +5 oxidation states (depending on redox potential), and its reactions in soils and sediments are influenced by pH, redox potential, dissolved organic or inorganic components, and sediment colloids (especially Fe sulfides and Fe, Mn, and Al oxides and hydroxides) and organic matter. Arsenic is often concentrated at the surfaces of suspended and sediment colloids (as surface adsorbed and occluded species or possibly as poorly ordered solid solutions). Arsenic (+3 and +5) is bound, by ligand bonding mechanisms, at the surfaces of solid phase Fe, Al and Mn oxides, though there are major descrepencies in the literature concerning the relative bonding strengths of arsenate and arsenite. These reactions at colloidal surfaces strongly influence its availability within the biosphere in oxidized systems. Arsenic (+3) is readily precipitated as As2S3 or coprecipitated in the FeS2 or FeS structure, and these compounds often control the solubility of arsenic in low redox environments. Because of these reactions, arsenic is likely strongly influenced by the presence of inorganic sulfur. The objectives of the study were as follows: 1. To characterize the concentrations and chemical forms of arsenic and the factors which influence its retention and release 2. To evaluate the role of the periodic oxidation/reduction processes that may occur in sediments on retention and release of arsenic 3. To evaluate the probable role of biologically induced processes (e.g., oxidation/reduction, acidification, and ligand exchange) which may influence the mobilization of precipitated or adsorbed arsenic 4. To develop surface dissolution procedures to assess heavy metal mobilization potential in sediments in the aquatic environment, with emphasis on calcareous stream bed sediments. The primary benefit of this study will be to improve procedures for assessing the bioavailability and potential biological hazard of metals in suspended solids and sediments. Accomplishment of these objectives has enabled us to recommend procedures for assessing biohazard potential and ultimately to better monitor aquatic environments

Nitrogen to phosphorus ratio of plant biomass versus soil solution in a tropical pioneer tree, Ficus insipida

It is commonly assumed that the nitrogen to phosphorus (N:P) ratio of a terrestrial plant reflects the relative availability of N and P in the soil in which the plant grows. Here, this was assessed for a tropical pioneer tree, Ficus insipida. Seedlings were grown in sand and irrigated with nutrient solutions containing N:P ratios ranging from <1 to >100. The experimental design further allowed investigation of physiological responses to N and P availability. Homeostatic control over N:P ratios was stronger in leaves than in stems or roots, suggesting that N:P ratios of stems and roots are more sensitive indicators of the relative availability of N and P at a site than N:P ratios of leaves. The leaf N:P ratio at which the largest plant dry mass and highest photosynthetic rates were achieved was ∼11, whereas the corresponding whole-plant N:P ratio was ∼6. Plant P concentration varied as a function of transpiration rate at constant nutrient solution P concentration, possibly due to transpiration-induced variation in the mass flow of P to root surfaces. The transpiration rate varied in response to nutrient solution N concentration, but not to nutrient solution P concentration, demonstrating nutritional control over transpiration by N but not P. Water-use efficiency varied as a function of N availability, but not as a function of P availability

Equisetum species show uniform epicuticular wax structures but diverse composition patterns

In the Equisetopsida, different wax distribution and composition patterns in the plant organs indicate a close relationship between wax structure and chemistry and the assimilatory function of these organs. Diverging wax compound classes show the two subgenera of Equisetum to be well separated

Two alanine aminotranferases link mitochondrial glycolate oxidation to the major photorespiratory pathway in Arabidopsis and rice

The major photorespiratory pathway in higher plants is distributed over chloroplasts, mitochondria, and peroxisomes. In this pathway, glycolate oxidation takes place in peroxisomes. It was previously suggested that a mitochondrial glycolate dehydrogenase (GlcDH) that was conserved from green algae lacking leaf-type peroxisomes contributes to photorespiration in Arabidopsis thaliana. Here, the identification of two Arabidopsis mitochondrial alanine:glyoxylate aminotransferases (ALAATs) that link glycolate oxidation to glycine formation are described. By this reaction, the mitochondrial side pathway produces glycine from glyoxylate that can be used in the glycine decarboxylase (GCD) reaction of the major pathway. RNA interference (RNAi) suppression of mitochondrial ALAAT did not result in major changes in metabolite pools under standard conditions or enhanced photorespiratroy flux, respectively. However, RNAi lines showed reduced photorespiratory CO2 release and a lower CO2 compensation point. Mitochondria isolated from RNAi lines are incapable of converting glycolate to CO2, whereas simultaneous overexpression of GlcDH and ALAATs in transiently transformed tobacco leaves enhances glycolate conversion. Furthermore, analyses of rice mitochondria suggest that the side pathway for glycolate oxidation and glycine formation is conserved in monocotyledoneous plants. It is concluded that the photorespiratory pathway from green algae has been functionally conserved in higher plants

Formation of the ηc\eta_c in Two-Photon Collisions at LEP

The two-photon width $\Gamma_{\gamma\gamma}$ of the $\eta_c$ meson has been measured with the L3 detector at LEP. The $\eta_c$ is studied in the decay modes $\pi^+\pi^-\pi^+\pi^-$, $\pi^+\pi^-$K$^+$K$^-$, K$_s^0$K$^\pm\pi^\mp$, K$^+$K$^-\pi^{0}$, $\pi^+\pi^-\eta$, $\pi^+\pi^-\eta'$, and $\rho^+\rho^-$ using an integrated luminosity of 140 pb$^{-1}$ at $\sqrt{s} \simeq 91$ GeV and of 52 pb$^{-1}$ at $\sqrt{s} \simeq 183$ GeV. The result is $\Gamma_{\gamma\gamma}(\eta_c) = 6.9 \pm 1.7 (stat.) \pm 0.8 (sys.) \pm 2.0$(BR) keV. The $Q^2$ dependence of the $\eta_c$ cross section is studied for $Q^2 < 9$ GeV$^{2}$. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a $\rho$-pole. In addition, a signal of $29 \pm 11$ events is observed at the $\chi_c0$ mass. Upper limits for the two-photon widths of the $\chi_c0$, $\chi_c2$, and $\eta_c'$ are also given

Direct Observation of Longitudinally Polarised W Bosons

The three different helicity states of W bosons, produced in the reaction e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of the scattering angle between the W- and the direction of the e- beam. The analysis demonstrates that W bosons are produced with all three helicities, the longitudinal and the two transverse states. Combining the results from the two center-of-mass energies and with leptonic and hadronic W decays, the fraction of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.) +/- 0.016(syst.) in agreement with the expectation from the Standard Model

Study of Z Boson Pair Production in e^+e^- Interactions at \sqrt{s}=192 - 202 GeV

The cross section for the production of Z boson pairs is measured using the data collected by the L3 detector at LEP in 1999 in e^+e^- collisions at centre-of-mass energies ranging from 192 GeV up to 202 GeV. Events in all the visible final states are selected, measuring the cross section of this process. The special case of final states containing b quarks is also investigated. All results are in agreement with the Standard Model predictions

Study of Z Boson Pair Production in e+e- Collisions at LEP at \sqrt{s}=189 GeV

The pair production of Z bosons is studied using the data collected by the L3 detector at LEP in 1998 in e+e- collisions at a centre-of-mass energy of 189 GeV. All the visible final states are considered and the cross section of this process is measured to be 0.74 +0.15 -0.14 (stat.) +/- 0.04 (syst.) pb. Final states containing b quarks are enhanced by a dedicated selection and their production cross section is found to be 0.18 +0.09 -0.07 (stat.) +/- 0.02 (syst.) pb. Both results are in agreement with the Standard Model predictions. Limits on anomalous couplings between neutral gauge bosons are derived from these measurements