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At least 19 recordsLinked to original sources
PubMed2001

The episodic acidification of small streams in the spring flood period of industrial polar region, Russia.

In Polar regions subject to acid precipitation, the spring flood period is swift and can be divided into three phases. In phase one, dilution and anion substitution by SO4 controls episodic acidification. Phase two is characterized by interaction of snowmelt water with the catchment. A combination of several factors contributes to declines in pH and ANC. In forest and wetland ecosystems, organic acids greatly contribute to the pH depression in the streams. In the coastal tundra and forest-tundra zones, "salt-effect" acidification predominantes. The increase in toxic forms of trace (Ni, Cu) and rare (Fe, Al, Mn) elements during pH depressions may create stress conditions for the fauna of polar fresh waters during a flood period.

Acid Rain↗
PubMed1981

Positional signalling along the anteroposterior axis of the chick wing. The effect of multiple polarizing region grafts.

We have proposed that positional information along the anteroposterior axis is specified by a signal from the polarizing region and that position may be specified by the concentration of a diffusible morphogen. While this model can account for a variety of results it is now clear that a model based on intercalation by growth of positional values can do the same. The distinction between the two models lies in whether a grafted polarizing region can alter existing positional values and in the distance over which it exerts its influence. The two models make different predictions as to the effect of grafting two polarizing regions. The intercalation model predicts that this effect will be the sum of two single grafts, whereas the morphogen model predicts different results depending on how close together the two polarizing regions are placed. The pattern of digits following grafts of two polarizing regions show that it is sensitive to the distance between the grafts and consistent with a model based on long-range interaction, such as a diffusible morphogen.

Animals↗
PubMed2002

The early history of the polarizing region: from classical embryology to molecular biology.

The polarizing region of the developing limb bud is one of the best known examples of a cell-cell signalling centre that mediates patterning in vertebrate embryos. This article traces some highlights in the history of the polarizing region from its discovery by John Saunders and early work that defined polarizing activity through a period in which modelling was pre-eminent, right up to the discovery of defined molecules with polarizing activity. There is a particular focus on the discovery that retinoic acid could mimic signalling of the polarizing activity and this finding is then set in the context of more recent work which implicates Shh and BMPs in mediating polarizing activity.

Animals↗
PubMed2004

Restricted Mobility of Cell Surface Proteins in the Polar Regions of Escherichia coli.

The polar regions of the Escherichia coli murein sacculus are metabolically inert and stable in time. Because the sacculus and the outer membrane are tightly associated, we investigated whether polar inert murein could restrict the mobility of other cell envelope elements. Cells were covalently labeled with a fluorescent reagent, chased in dye-free medium, and observed by microscopy. Fluorescent material was more efficiently retained at the cell poles than at any other location. The boundary between high and low fluorescence intensity areas was rather sharp. Labeled material consisted mostly of cell envelope proteins, among them the free and murein-bound forms of Braun's lipoprotein. Our results indicate that the mobility of at least some cell envelope proteins is restrained at regions in correspondence with underlying areas of inert murein.

Amdinocillin↗
PubMed1992

The influence of charge and the distribution of charge in the polar region of phospholipids on the activity of UDP-glucuronosyltransferase.

Studies of the mechanism of lipid-induced regulation of the microsomal enzyme UDP-glucuronosyltransferase have been extended by examining the influence of charge within the polar region on the ability of lipids to activate delipidated pure enzyme. The effects of net negative charge, of charge separation in phosphocholine, and of the distribution of charge in the polar region of lipids were studied using the GT2p isoform isolated from pig liver. Prior experiments have shown that lipids with net negative charge inhibit the enzyme (Zakim, D., Cantor, M., and Eibl, H. (1988) J. Biol. Chem. 263, 5164-5169). The current experiments show that the extent of inhibition on a molar basis increases as the net negative charge increases from -1 to -2. The inhibitory effect of negatively charged lipids is on the functional state of the enzyme and is not due to electrostatic repulsion of negatively charged substrates of the enzyme. Although the inhibitory effect of net negative charge is removed when negative charge is balanced by a positive charge due to a quaternary nitrogen, neutrality of the polar region is not a sufficient condition for activation of the enzyme. In addition to a balance of charge between Pi and the quaternary nitrogen, the distance between the negative and positive charges and the orientation of the dipole created by them are critical for activation of GT2p. The negative and positive charges must be separated by the equivalent of three -CH2- groups for optimal activation by a lipid. Shortening this distance by one -CH2- unit leads to a lipid that is ineffective in activating the enzyme. Reversal of the orientation of the dipole in which the negative charge is on the polymethylene side of the lipid-water interface and the positive charge extends into water also produces a lipid that is not effective for activating GT2p. On the other hand, lipids with phosphoserine as the polar region, which has the "normal" P-N distance but carries a net negative charge, do not inhibit GT2p. This result again illustrates the importance of the dipole of phosphocholine for modulating the functional state of GT2p.

Animals↗
PubMed2001

Marine macroalgae in polar regions as natural sources for volatile organohalogens.

Marine macroalgae species from the polar regions were investigated for their importance as natural sources of volatile halogenated compounds released into the biosphere. Several different halogenated C1 to C4 hydrocarbons were identified and their release rates determined. The compounds contained mainly bromine and iodine, and form was the dominant compound released. Although an annual atmospheric input of approximately 10(8)-10(10) g bromine and 10(7)-10(8) g iodine was calculated from the release rates, marine macroalgae are apparently not the major source on a global scale, as the release is up to four orders of magnitude lower than a presumed annual flow from the oceans. Despite this, macroalgae may be more important on a local scale due to their occurrence at a high biomass in the coastal regions. The present paper gives an overview about studies done on the release of volatile halocarbons by macroalgae from polar regions. Furthermore, the function of these compounds in the macroalgal metabolism is discussed.

Cold Climate↗
PubMed1983

Does anterior (non-polarizing region) tissue signal in the developing chick limb?

The morphogenetic properties of embryonic chick limb bud tissue from anterior positions and from the posterior (polarizing) region are compared. Quail grafts, which possess the distinctive nucleolar cell marker, and gamma-irradiation are used. Supernumerary limb structures induced by anterior tissue wedge grafts are found to be nearly exclusively graft, donor tissue derived. This contrasts with the duplicate limb structures formed in response to posterior (polarizing region) tissue grafts in which host cells predominate. Distinction between anterior and posterior tissue properties was also demonstrated using doses of radiation (approximately 12 Gy = 1200 rad) which inhibit cell proliferation, but have negligible effects on avian polarizing activity. These doses, however, are found to completely abolish morphogenetic activity by chick or quail anterior tissue grafts. The results of anterior (non-polarizing) region tissue grafts are best interpreted as graft self-differentiation under the influence of a posterior signalling region, whose properties in the limb bud are demonstrably unique.

Animals↗
PubMed2003

Subfreezing activity of microorganisms and the potential habitability of Mars' polar regions.

The availability of water-ice at the surface in the Mars polar cap and within the top meter of the high-latitude regolith raises the question of whether liquid water can exist there under some circumstances and possibly support the existence of biota. We examine the minimum temperatures at which liquid water can exist at ice grain-dust grain and ice grain-ice grain contacts, the minimum subfreezing temperatures at which terrestrial organisms can grow or multiply, and the maximum temperatures that can occur in martian high-latitude and polar regions, to see if there is overlap. Liquid water can exist at grain contacts above about -20 degrees C. Measurements of growth in organisms isolated from Siberian permafrost indicate growth at -10 degrees C and metabolism at -20 degrees C. Mars polar and high-latitude temperatures rise above -20 degrees C at obliquities greater than ~40 degrees, and under some conditions rise above 0 degrees C. Thus, the environment in the Mars polar regions has overlapped habitable conditions within relatively recent epochs, and Mars appears to be on the edge of being habitable at present. The easy accessibility of the polar surface layer relative to the deep subsurface make these viable locations to search for evidence of life.

Bacteria↗
PubMed1990

Expression of a homeobox gene in the chick wing bud following application of retinoic acid and grafts of polarizing region tissue.

Homeobox gene XlHbox 1 is expressed in a mesodermal gradient in vertebrate forelimbs with maximal expression anteriorly and proximally and may encode positional values. In chick wing buds, anterior cells can be reprogrammed to form posterior structures by grafts of polarizing region tissue and by beads soaked in retinoic acid (RA), which is a good candidate for an endogenous morphogen. Applications of RA anteriorly or at the bud apex, treatments which produce duplicated digits or truncations respectively, substantially increase the extent of mesodermal XlHbox 1 expression. Polarizing region grafts that also produce additional digits lead to a moderate increase. The effects of RA application and the behaviour of transplanted tissue show that only anterior cells are competent to express XlHbox 1 and that expression is cell autonomous. Ectodermal expression in wing buds is enhanced by RA but not by polarizing region grafts and ectoderm/mesoderm recombinations show that the mesoderm is irreversibly affected. The changes in mesodermal expression do not fit the predictions of the simple model that XlHbox 1 encodes anterior positional values but are correlated with a series of novel malformations of the shoulder girdle which, in normal wing buds, is derived from cells expressing XlHbox 1.

Animals↗
PubMed1985

Local dielectric properties around polar region of lipid bilayer membranes.

Local dielectric constant was evaluated from the Stokes shifts of fluorescence spectra of L-alpha-dansylphosphatidylethanolamine (DPE) incorporated into liposomes made of synthetic phosphatidylcholine (dipalmitoyl or distearoyl) or bovine brain phosphatidylserine. The evaluation was established as follows. First, the Stokes shift of DPE was assured to follow Mataga-Lippert's equation and was a function of the dielectric constant and the refractive index in some standard organic solvents. Second, the change of the refractive index did not contribute much to the change in the Stokes shift. Third, the time resolved fluorescence depolarization of DPE in liposomes showed that the cone wobbling diffusion was rapid relative to the fluorescence lifetime and therefore that the dielectric relaxation did not affect the evaluation of the constant in the polar region of membranes. We then investigated the characteristics of the local dielectric constant in the polar region of the lipid bilayer and found that the dielectric constant varies between 4 and 34 depending upon calcium binding and also gel/liquid-crystal phase transition. Such large changes of the local dielectric constant were further correlated with the dynamic structure of lipid bilayer membranes measured by conventional fluorescence depolarization techniques. The large changes of dielectric constant around the polar region suggest that electrostatic interactions at this region can be altered 10-fold by such ionic or thermotropic factors and therefore that local dielectric properties can play crucial roles in membrane functions.

Dansyl Compounds↗
PubMed1981

The number of polarizing region cells required to specify additional digits in the developing chick wing.

A group of mesenchyme cells at the posterior margin of the developing wing-the polarizing region-can have a dramatic effect on the pattern of structures which develop across the antero-posterior axis of the limb. If one grafts a polarizing region to the anterior margin of a wing bud so that this bud now has one polarizing region at the anterior margin and one at the posterior margin, the wing that develops has duplicated structures across the antero-posterior axis in mirror-image symmetry. That is, the normal pattern of digits 2 3 4 (reading from anterior to posterior) becomes 4 3 2 2 3 4. The ability of the polarizing region to specify additional digits from adjacent tissue can be progressively attenuated by gamma-ray radiation. If this attenuation is caused by progressively fewer cells remaining viable to signal, there should be a quantitative relationship between the number of polarizing cells used and the digit specified next to the graft. Here, two tests are reported which confirm this idea. The results suggest that the apical ridge cooperates with a small number of polarizing region cells in a monolayer to specify structures across the anterio-posterior axis of the wing.

Animals↗
PubMed1980

Special characteristics of the polar regions of the rat lens: morphology and phosphatase histochemistry.

Ultrastructural analyses of the normal rat lens revealed a number of characteristics present regionally within the anterior and posterior polar regions: (1) elaborate folding of the plasma membrane, including numerous microvillar processes; (2) wide intercellular spaces at basolateral cell borders; (3) concentrations of mitochondria; and (4) ouabain-sensitive Na-K-ATPase activity. These features, confined primarily to the suture systems and the anterior epithelium, suggested a cortical as well as an epithelial involvement in ion-linked fluid transport, supporting recent physiological investigations of the lens. Acid phosphatase localized in aggregations of smooth endoplasmic reticulum at the lens fiber ends suggested that this micro-organelle may be a source of acid hydrolases in the normal lens.

Acid Phosphatase↗
PubMed1993

Extension of the parallax analysis of membrane penetration depth to the polar region of model membranes: use of fluorescence quenching by a spin-label attached to the phospholipid polar headgroup.

The parallax method is a method by which the depth of fluorescent molecules within a membrane is calculated from the ratio of quenching induced by two spin-labeled phospholipids at different depths. In this report, the method is extended to measurements of depth in the polar headgroup region of the membrane through use of a lipid with a spin-label attached to the polar choline moiety. Quenching data indicate that the choline-attached nitroxide is close to 19.5 A from the bilayer center, in good agreement with the choline location previously determined by diffraction measurements. By using quenching results obtained with this polar headgroup-labeled phospholipid, depths more accurate than those measured previously can be obtained for fluorophores in the polar region of the membrane. It appears that the most reliable results are obtained when depth is calculated from the quenching of the two spin-labels that quench a specific fluorophore most strongly. Applying this approach to a series of anthroyloxy-labeled fatty acids indicates that the depth of the anthroyloxy group is almost linearly related to the number of carbon atoms between it and the carboxyl group. The fatty acid carboxyl group itself is close to 18.6 A from the bilayer center in the ionized form and 16 A from bilayer center in the protonated form. This is close to the depth of the carboxyl groups on phospholipid fatty acyl chains. More accurate depths have also been obtained for 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD) labeled phospholipids using the quenching of the choline-attached spin-label.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Chloro-7-nitrobenzofurazan↗
PubMed1978

Influence of cholesterol on the polar region of phosphatidylcholine and phosphatidylethanolamine bilayers.

The structural changes in the polar head group region of unsonicated bilayer membranes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine produced by addition of cholesterol have been determined using deuterium and phosphorus-31 NMR. Incorportion of up to 50 mol percent cholesterol produces little change in the phosphorus-31 chemical shielding anisotropies, compared with the values in pure bilayers above the phase transition temperatures, while some of the deuterium quadrupole splittings are reduced by almost a factor of two. Adjustment of the head group torsion angles by only a few degrees accounts for the observed spectral changes. Addition of cholesterol therefore has opposite effects on the hydrocarbon and polar regions of membranes: although cholesterol makes the hydrocarbon region gel-like, with an increased probability of trans conformations, the conformation of the polar head groups is very similar to that found in the liquid crystalline phase of pure phospholipid bilayers.

Chemical Phenomena↗
PubMedDate not supplied

[Analysis of the daily human requirements for thiamine in the newly arrived population of Polar regions].

The erythrocytes transketolase activity and the TDP-effect were determined in persons residing in the regions beyond the polar circle and these demonstrated a moderate thiamine deficiency. The daily thiamine intake with food in the examined did not exceed 1.5 mg, the thiamine-diphosphate of the epoenzyme amounting to 90 per cent. Following introduction of various pharmacological preparations of vitamin B1 for a space of 2 weeks a somewhat greater transketolase activity and a diminution of the TDP-effect were observed. Administration of cocarboxylase and vitamin B1 with Mg and gelatin more favourable changes were obtained. Some macro- and micro-elements were found to exercise a positive effect on the thiamine assimilation by the tissues. The results obtained indicate that the daily thiamine requirement (allowance) of man in the North does not surpass 1.5-2.0 mg. To control hypovitaminoses in the North it is more effective to use natural vitamin-carriers rather than pharmacological preparations of vitamin B1.

Adolescent↗
PubMed2002

[Effects of the factor of season on the the physiological status of petroleum industry workers in the Polar region].

There were three medical examinations (in March, June and October) of oilers on shift days 5-6 in a field medical post in the Polar region. The survey protocol included analysis of morning (before breakfast) biochemical and cell indices, physiological examination, testing reactions to standard stimuli (color, tone), psychological testing, assessment of factual nutrition, analysis of the cardiorespiratory function at rest and during physical tests. It was stated that recovery of physical performance varied with the seasons. In March, the shift workers were significantly less reactive to the color stimulus. At low ambient temperature (-38 degrees C) blood content of alpha 1- and alpha 2-globulins went up, and there were atypical proteins and considerable amounts of total cholesterol, pre-beta-lipoproteins and alpha-lipoproteins in blood.

Anthropometry↗
PubMed1998

Observations of the north polar region of Mars from the Mars orbiter laser altimeter.

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.

Carbon Dioxide↗