Factors influencing plasma zinc levels in low-income pregnant women

Plasma zinc (Zn) concentrations were measured in 4376 indigent women (86% African-American), at a mean (±SD) gestational age of 15 (±7.8) wk to determine the relationship between various maternal characteristics and plasma Zn levels during pregnancy. Mean plasma Zn levels were lower in African-American women than in Caucasian women, in multiparous women than in primiparous women, and in women with body weight >69.9 kg than in those with body weight ≤69.9 kg (p≤0.001 for each comparison). There were no significant differences related to maternal age, marital status, education, or smoking habit. Multiple regression analysis, including maternal prepregnancy weight, race, age, parity, smoking habit, education, and marital status indicated that race, parity, and pregnancy weight were significantly associated with maternal plasma Zn levels, adjusted for gestational age. Maternal race was the best predictor of plasma Zn concentrations among the population of pregnant women studied A significant proportion of variance in maternal plasma Zn levels remained unexplained after taking into account various maternal characteristics. The reasons for lower plasma Zn levels in African-American women, compared to Caucasian women, during pregnancy are unknown.     

Reduced levels of cytochrome b 6/f in transgenic tobacco increases the excitation pressure on Photosystem II without increasing sensitivity to photoinhibition in vivo

We have examined tobacco transformed with an antisense construct against the Rieske-FeS subunit of the cytochromeb ₆ f complex, containing only 15 to 20% of the wild-type level of cytochrome f. The anti-Rieske-FeS leaves had a comparable chlorophyll and Photosystem II reaction center stoichiometry and a comparable carotenoid profile to the wild-type, with differences of less than 10% on a leaf area basis. When exposed to high irradiance, the anti-Rieske-FeS leaves showed a greatly increased closure of Photosystem II and a much reduced capacity to develop non-photochemical quenching compared with wild-type. However, contrary to our expectations, the anti-Rieske-FeS leaves were not more susceptible to photoinhibition than were wild-type leaves. Further, when we regulated the irradiance so that the excitation pressure on photosystem II was equivalent in both the anti-Rieske-FeS and wild-type leaves, the anti-Rieske-FeS leaves experienced much less photoinhibition than wild-type. The evidence from the anti-Rieske-FeS tobacco suggests that rapid photoinactivation of Photosystem II in vivo only occurs when closure of Photosystem II coincides with lumen acidification. These results suggest that the model of photoinhibition in vivo occurring principally because of limitations to electron withdrawal from photosystem II does not explain photoinhibition in these transgenic tobacco leaves, and we need to re-evaluate the twinned concepts of photoinhibition and photoprotection.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlophenyl)-1,-dimethylurea - Fo and Fo minimal fluorescence when all PS II reaction centers are open in dark- and light-acclimated leaves, respectively - Fm and Fm maximal fluorescence when all PS II reaction centers are closed in dark- and light-acclimated leaves, respectively - Fv variable fluorescence (Fm-Fo) in dark acclimated leaves - Fv variable fluorescence (Fm-Fo) in lightacclimated leaves - NPQ non-photochemical quenching of fluorescence - PS I and PS II Photosystem I and II - P680 primary electron donor of the reaction center of PS II - PFD photosynthetic flux density - Q_A primary acceptor quinone of PS II - q_p photochemical quenching of fluorescence - V+A+Z violaxanthin+antheraxanthin+zeaxanthin     

A laboratory-based method to measure relative pesticide and spray oil efficacy against broad mite, Polyphagotarsonemus latus (Banks)(Acari: Tarsonemidae)

Six pesticides and two spray oils were tested against Polyphagotarsonemus latus. The chemicals were evaluated under laboratory conditions, requiring the development of a novel bioassay method, which is reported here. The pesticide toxicities fell into three distinct groups, namely abamectin, conventional pesticides and oils. The relative pesticide toxicities at the LC₅₀ level were abamectin 4.9×10^-8 g ai l^-1, endosulfan 1.1×10^-3 g ai l^-1, fenpyroximate 2.3×10^-3 g ai l^-1, pyridaben 4.1×10^-3 g ai l^-1, tebufenpyrad 4.4×10^-3 g ai l^-1, dicofol 4.5×10^-3 g ai l^-1, petroleum spray oil 3.4×10^-1 g ai l^-1 and canola oil 4.1×10^-1 g ai l^-1. The calculation of the LC_99.9 values allows for resistance monitoring in P. latus and the suggested discriminating concentrations are abamectin 1.0×10^-4 g ai l^-1; endosulfan, pyridaben and dicofol 1.0×10^-1 g ai l^-1 fenpyroximate and tebufenpyrad 5.0×10^-1 g ai l^-1.     

Geochemistry of aquatic humic substances in the Lake Fryxell Basin, Antarctica

Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem¹⁴C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat.     

Application of the integrated lake-watershed acidification study model to watershed liming at woods Lake,New York

Woods Lake, in the Adirondack Mountains of New York, was the site of the Experimental Watershed Liming Study (EWLS) in which base addition was investigated as a method for mitigation of lake acidity. In an effort to predict the duration of effects, the treatment was simulated using the Integrated Lake-Watershed Acidification Study (ILWAS) model. To simulate terrestrial liming, calcite was applied to treated subcatchments as a rapidly weathering mineral in the upper horizon. Soil solution and lake outlet chemistry showed a response to calcite addition within four months of the start of the simulation. Calcium concentrations, acid neutralizing capacities (ANC), and pH increased in the upper soil layer and aluminum concentrations decreased in the upper three soil layers (0–70 cm). The response of ANC was delayed in lower soil layers due to proton production associated with aluminum hydrolysis. Moreover, soil water pH in the third soil layer decreased in response to calcite treatment due to the displacement of hydrogen ions by calcium added to the exchange complex. Calcium concentrations, ANC and pH increased and aluminum concentrations decreased in the simulated lake outlet. The modeled effects of calcite treatment on the soil and lake outlet chemistry were not as great as field observations. This was, in part, attributed to the model representation of the watershed, which did not include streams, ponds, or wetlands located in the treated subcatchments. Calcite applied to these saturated areas in the field readily dissolved, supplying ANC to lake water. Additionally, incorporation of calcite into a thick organic layer in the model diminished the possibility of dissolution by contact with overland flow. Observed concentrations of calcium, ANC, and pH in the outlet decreased after high values in the two years after treatment. Although the model failed to match observed short-term data, it may simulate the long-term response as calcium is transported through the soil. A long-term simulation of the model suggests that effects of base treatment will persist for at least 50 years.     

Homologues of the human multidrug resistance genes MRP and MDR contribute to heavy metal resistance in the soil nematode Caenorhabditis elegans.

Acquired resistance of mammalian cells to multiple chemotherapeutic drugs can result from enhanced expression of the multidrug resistance-associated protein (MRP), which belongs to the ABC transporter superfamily. ABC transporters play a role in the protection of organisms against exogenous toxins by cellular detoxification processes. We have identified four MRP homologues in the soil nematode Caenorhabditis elegans, and we have studied one member, mrp-1, in detail. Using an mrp::lacZ gene fusion, mrp-l expression was found in cells of the pharynx, the pharynx-intestinal valve and the anterior intestinal cells, the rectum-intestinal valve and the epithelial cells of the vulva. Targeted inactivation of mrp-l resulted in increased sensitivity to the heavy metal ions cadmium and arsenite, to which wild-type worms are highly tolerant. The most pronounced effect of the mrp-1 mutation is on the ability of animals to recover from temporary exposure to high concentrations of heavy metals. Nematodes were found to be hypersensitive to heavy metals when both the MRP homologue, mrp-1, and a member of the P-glycoprotein (Pgp) gene family, pgp-1, were deleted. We conclude that nematodes have multiple proteins, homologues of mammalian proteins involved in the cellular resistance to chemotherapeutic drugs, that protect them against heavy metals.     

Ethylene production and involvement during the first steps of durum wheat (Triticum durum) anther culture

The role of ethylene in anther culture of durum wheat ( Triticum durum Desf. cv. Ardente) was analyzed by testing the effects of 2-chloroethylphosphonic acid (ethrel) silver thiosulfate (Ag⁺), a -aminooxyacetic acid (AOA) and 1-aminocyclopropane-l-carboxylic acid (ACC) on microspore division observed after 21 days of culture and on development of calli estimated at day 45. The use of ethrel and Ag⁺ indicated a positive effect of ethylene on microspore division, whereas the use of AOA, and to a lesser extent ACC, snowed a negative effect. In contrast, the addition of ethrel or Ag⁺ indicated that ethylene inhibits the development of microspore-derived calli. AOA gave contradictory results. Ethylene production by anthers was about 7 pl anther⁻¹h⁻¹ and decreased during culture. ACC content in the anthers was maximal at day 9, whereas malonyl ACC (MACC) increased sharply from day 0 to day 3 and then decreased. The addition of AOA or ACC to the culture medium decreased or increased, respectively, ethylene production of anthers and the ACC and/or MACC content, but at concentrations higher than those that modified the formation of calli. This formation seems to occur in two successive phases: induction and initiation of microspore division, which was promoted by ethylene, followed by callus development, which was inhibited by ethylene.     

Germination in spores of Dryopteris filix-mas: Regulation of rhizoid elongation as a second phytochrome-mediated response

Spore germination in Dryopteris filix-mas occurs via a cascade of cellular responses, and chlorophyll formation, mitosis or rhizoid elongation are commonly used as parameters to determine spore germination. Detailed investigations of these parameters led to the hypothesis that they are regulated by different, independent phytochrome-mediated responses. This concept could be confirmed, as is described in this paper which demonstrates that perception of light via phytochrome occurs within two different phases separated in time. Presence of the far-red absorbing phytochrome form, P_fr, for 36 h, induces chlorophyll formation and the first unequal cell division, by which a rhizoid initial and a protonemal initial are formed (first phytochrome-mediated response). However, rhizoid elongation requires a second period of P_fr, presence (second phytochrome-mediated response). There is a clear temporal distinction between the first and the second phytochrome-mediated response with respect to the coupling of P_fr to the transduction chain; P_fr is unable to induce rhizoid growth until 60 h after the start of the first red irradiation. The effectivity of P_fr for inducing the second response shows an optimum at ca 96 h after the beginning of the presence of P_fr; thereafter, it declines slowly. The fluence-response relationship and the presence of red/far-red reversibility demonstrate that rhizoid elongation is a low-fluence response mediated by phytochrome and is independent of the first phytochrome response.     

15N natural abundance in forest and pasture soils of the Brazilian Amazon Basin

The natural abundance of ¹⁵N was examined in soil profiles from forests and pastures of the Brazilian Amazon Basin to compare tropical forests on a variety of soil types and to investigate changes in the sources of nitrogen to soils following deforestation for cattle ranching. Six sites in the state of Rondônia, two sites in Pará and one in Amazonas were studied. All sites except one were chronosequences and contained native forest and one or more pastures ranging from 2 to 27 years old. Forest soil ¹⁵N values to a depth of 1 m ranged from 8 to 23 and were higher than values typically found in temperate forests. A general pattern of increasing ¹⁵N values with depth near the soil surface was broadly similar to patterns in other forests but a decrease in ¹⁵N values in many forest profiles between 20 and 40 cm suggests that illuviation of ¹⁵N-depleted nitrate may influence total soil ¹⁵N values in deeper soil where total N concentrations are low. In four chronosequences in Rondônia, the ¹⁵N values of surface soil from pastures were lower than in the original forest and ¹⁵N values were increasingly depleted in older pastures. Inputs of atmospheric N by dinitrogen fixation could be an important N source in these pastures. Other pastures in Amazonas and Pará and Rondônia showed no consistent change from forest values. The extent of fractionation that leads to ¹⁵N enrichment in soils was broadly similar over a wide range of soil textures and indicated that similar processes control N fractionation and loss under tropical forest over a broad geographic region. Forest ¹⁵N profiles were consistent with conceptual models that explain enrichment of soil ¹⁵N values by selective loss of ¹⁴N during nitrification and denitrification.