Isolation of an actin polymerization stimulator from bovine thyroid plasma membranes

An actin polymerization stimulator was purified from bovine thyroid plasma membranes by DNase I affinity column chromatography. Although the molecular weight of the protein was about 42,000 (42K) by sodium dodecyl sulfate polyacrylamide gel electrophoresis, it did not comigrate with actin. In the presence of 30 mM KCl, the 42K protein facilitated formation of actin filaments when analyzed by a centrifugation method, accelerated the initial phase of actin polymerization as measured in an Ostwald viscometer and increased the length of filaments as shown by electron microscopy. The 42K protein also accelerated the initial phase of actin polymerization in the presence of 100 mM KCl and 2 mM MgCl₂ but did not affect the final viscosity. The effect of the 42K protein was diminished by 5 uM cytochalasin B or 1 uM cytochalasin D. This 42K protein may anchor actin filaments onto the thyroid plasma membrane.     

Production and Fungitoxicity of the Terpenoid Phytoalexins in Cotton Inoculated with Fusarium oxysporum f. sp. vasinfectum

Four terpenoid phytoalexins, desoxyhemigossypol (dHG), hemigossypol (HG), desoxyhemigossypol- 6-methyl ether (dMHG) and hemigossypol-6-methyl ether (MHG), were identified with HPLC analysis of extracts from the moderately Fusarium wilt resistant cotton var. TAMCOT CAMD-E ( Gossypium hirsutum ) inoculated with Fusarium oxysporum f. sp. vasinfectum (F. o. v.). Concentrations of dHG, HG, dMHG and MG in stem steles at 10 days after inoculation were 45.1, 175. 0, 38. 3 and 1. 6 (g g^–1 fresh tissue, respectively. The bioassays demonstrated that all four phytoalexins were toxic to F. o. v. The ED₅₀'s of dHG, dMHG and HG were calculated as 8. 8, 13. 4 and 29. 3 (g ml⁻¹, respectively. The very low solubility of MHG in the standard assay medium prevented the determination of its ED₅₀ value. Only dHG is water soluble at levels that appear necessary to act as an effective phytoalexin. At 30 μg ml⁻¹, dHG kills all conidia and mycelia of F. o. v . Viable propagules of F. o. v. were recovered from the steles of inoculated plants 10 days after inoculation; however, the pathogen was restricted to a zone 15 cm above the hypocotyl inoculation site. Thus, the fungistatic action of dHG appears to contribute to the resistance of cotton to Fusarium wilt by preventing the systemic distribution of F. o. v . propagules.     

Effects of dichloroacetate and glyoxylate on low density lipoprotein uptake and on growth of cultured fibroblasts

The effects of dichloroacetate, a known hypocholesterolemic agent, were studied in cultured growing and confluent human fibroblast cells. Microscopic examination showed no visible adverse effects of dichloroacetate on confluent cells during exposure to concentrations as high as 5 mM for 96 hr. Higher concentrations resulted in cell death after varying periods of incubation. There were no viable cells after 24 hr of exposure to 100 mM dichloroacetate. In contrast, much lower concentrations proved lethal to growing cells; cell growth, as determined by cell numbers at specified times after splitting, was suppressed by 1 mM dichloroacetate and 5 mM concentrations resulted in cell death. Similar effects were noted with glyoxylate. The hypocholesterolemic effect of dichloroacetate is probably not due to any effect on the low density lipoprotein pathway, since concentrations of up to 1 mM dichloroacetate did not affect the cellular binding and uptake of 125I-labeled low density lipoprotein. It is concluded that growing and rapidly metabolizing cells are much more sensitive to the toxic effects of dichloroacetate and glyoxylate than confluent cells.     

The biogeochemistry of phosphorus after the first century of soil development on Rakata Island, Krakatau, Indonesia

This study examined the accumulation of organic carbon (C) and fractions ofsoil phosphorus (P) in soils developing in volcanic ash deposited in the1883 eruption of Krakatau. Organic C has accumulated at rates of 45 to 127g/m²/yr during 110 years of soil development, resulting inprofiles with as much as 14 kgC/m². Most soil P is found inthe HCl-extractable forms, representing apatite. A loss of HCl-extractableP from the surface horizons is associated with a marked accumulation ofNaOH-extractable organic P bound to Al. A bioassay with hill rice suggeststhat P is limiting to plant growth in these soils, perhaps as a result ofthe rapid accumulation of P in organic forms.     

A new method for identifying rapid decline dynamics in wild vertebrate populations

Tracking trends in the abundance of wildlife populations is a sensitive method for assessing biodiversity change due to the short time‐lag between human pressures and corresponding shifts in population trends. This study tests for proposed associations between different types of human pressures and wildlife population abundance decline‐curves and introduces a method to distinguish decline trajectories from natural fluctuations in population time‐series. First, we simulated typical mammalian population time‐series under different human pressure types and intensities and identified significant distinctions in population dynamics. Based on the concavity of the smoothed population trend and the algebraic function which was the closest fit to the data, we determined those differences in decline dynamics that were consistently attributable to each pressure type. We examined the robustness of the attribution of pressure type to population decline dynamics under more realistic conditions by simulating populations under different levels of environmental stochasticity and time‐series data quality. Finally, we applied our newly developed method to 124 wildlife population time‐series and investigated how those threat types diagnosed by our method compare to the specific threatening processes reported for those populations. We show how wildlife population decline curves can be used to discern between broad categories of pressure or threat types, but do not work for detailed threat attributions. More usefully, we find that differences in population decline curves can reliably identify populations where pressure is increasing over time, even when data quality is poor, and propose this method as a cost‐effective technique for prioritizing conservation actions between populations.