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Sökning: L773:0028 0836 OR L773:1476 4687 > (2010-2019) > (2019)

  • Resultat 21-30 av 62
  • Föregående 12[3]4567Nästa
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21.
  • Kardol, Paul (författare)
  • Soil nematode abundance and functional group composition at a global scale
  • 2019
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 572
  • Tidskriftsartikel (refereegranskat)abstract
    • Soil organisms are a crucial part of the terrestrial biosphere. Despite their importance for ecosystem functioning, few quantitative, spatially explicit models of the active belowground community currently exist. In particular, nematodes are the most abundant animals on Earth, filling all trophic levels in the soil food web. Here we use 6,759 georeferenced samples to generate a mechanistic understanding of the patterns of the global abundance of nematodes in the soil and the composition of their functional groups. The resulting maps show that 4.4 +/- 0.64 x 10(20) nematodes (with a total biomass of approximately 0.3 gigatonnes) inhabit surface soils across the world, with higher abundances in sub-Arctic regions (38% of total) than in temperate (24%) or tropical (21%) regions. Regional variations in these global trends also provide insights into local patterns of soil fertility and functioning. These high-resolution models provide the first steps towards representing soil ecological processes in global biogeochemical models and will enable the prediction of elemental cycling under current and future climate scenarios.
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22.
  • Korablev, Oleg, et al. (författare)
  • No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations
  • 2019
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 568, s. 517-520
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations2,3,4,5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere6,7, which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane1,6,8. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.</p>
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23.
  • Lindgren, Johan, et al. (författare)
  • Fossil insect eyes shed light on trilobite optics and the arthropod pigment screen
  • 2019
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 573:7772, s. 122-125
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Fossilized eyes permit inferences of the visual capacity of extinct arthropods1–3. However, structural and/or chemical modifications as a result of taphonomic and diagenetic processes can alter the original features, thereby necessitating comparisons with modern species. Here we report the detailed molecular composition and microanatomy of the eyes of 54-million-year-old crane-flies, which together provide a proxy for the interpretation of optical systems in some other ancient arthropods. These well-preserved visual organs comprise calcified corneal lenses that are separated by intervening spaces containing eumelanin pigment. We also show that eumelanin is present in the facet walls of living crane-flies, in which it forms the outermost ommatidial pigment shield in compound eyes incorporating a chitinous cornea. To our knowledge, this is the first record of melanic screening pigments in arthropods, and reveals a fossilization mode in insect eyes that involves a decay-resistant biochrome coupled with early diagenetic mineralization of the ommatidial lenses. The demonstrable secondary calcification of lens cuticle that was initially chitinous has implications for the proposed calcitic corneas of trilobites, which we posit are artefacts of preservation rather than a product of in vivo biomineralization4–7. Although trilobite eyes might have been partly mineralized for mechanical strength, a (more likely) organic composition would have enhanced function via gradient-index optics and increased control of lens shape.</p>
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24.
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25.
  • McFiggans, Gordon, et al. (författare)
  • Secondary organic aerosol reduced by mixture of atmospheric vapours
  • 2019
  • Ingår i: Atmosfärisk oxidation av stress-inducerade emissioner från växtlighet - dess roll för aerosolbildning.
  • Tidskriftsartikel (refereegranskat)abstract
    • Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene ‘scavenges’ hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).
26.
  • Melnyk, Charles (författare)
  • Mobile PEAR transcription factors integrate positional cues to prime cambial growth
  • 2019
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 565, s. 490-494
  • Tidskriftsartikel (refereegranskat)abstract
    • Apical growth in plants initiates upon seed germination, whereas radial growth is primed only during early ontogenesis in procambium cells and activated later by the vascular cambium(1). Although it is not known how radial growth is organized and regulated in plants, this system resembles the developmental competence observed in some animal systems, in which pre-existing patterns of developmental potential are established early on(2,3). Here we show that in Arabidopsis the initiation of radial growth occurs around early protophloem-sieve-element cell files of the root procambial tissue. In this domain, cytokinin signalling promotes the expression of a pair of mobile transcription factors-PHLOEM EARLY DOF 1 (PEAR1) and PHLOEM EARLY DOF 2 (PEAR2)-and their four homologues (DOF6, TMO6, OBP2 and HCA2), which we collectively name PEAR proteins. The PEAR proteins form a short-range concentration gradient that peaks at protophloem sieve elements, and activates gene expression that promotes radial growth. The expression and function of PEAR proteins are antagonized by the HD-ZIP III proteins, well-known polarity transcription factors(4)-the expression of which is concentrated in the more-internal domain of radially non-dividing procambial cells by the function of auxin, and mobile miR165 and miR166 microRNAs. The PEAR proteins locally promote transcription of their inhibitory HD-ZIP III genes, and thereby establish a negative-feedback loop that forms a robust boundary that demarks the zone of cell division. Taken together, our data establish that during root procambial development there exists a network in which a module that links PEAR and HD-ZIP III transcription factors integrates spatial information of the hormonal domains and miRNA gradients to provide adjacent zones of dividing and more-quiescent cells, which forms a foundation for further radial growth.
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27.
  • Mäkinen, Taija (författare)
  • Neurobiology : A Drain At The Base Of The Brain
  • 2019
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 572:7767, s. 34-35
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • <p>A set of lymphatic vessels that wrap around the base of the mouse brain have been shown to drain fluid from the brain into the peripheral lymphatic system, and to exhibit a decline in function with ageing.</p>
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28.
  • NCD Risk Factor Collaboration (NCD-RisC) (författare)
  • Rising rural body-mass index is the main driver of the global obesity epidemic in adults
  • 2019
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 569:7755, s. 260-264
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities<sup>1,2</sup>. This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity<sup>3,4,5,6</sup>. Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017—and more than 80% in some low- and middle-income regions—was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing—and in some countries reversal—of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.</p>
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29.
  • Newton, Phillip T., et al. (författare)
  • A radical switch in clonality reveals a stem cell niche in the epiphyseal growth plate
  • 2019
  • Ingår i: Nature. - NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 567:7747, s. 234-
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Longitudinal bone growth in children is sustained by growth plates, narrow discs of cartilage that provide a continuous supply of chondrocytes for endochondral ossification 1 . However, it remains unknown how this supply is maintained throughout childhood growth. Chondroprogenitors in the resting zone are thought to be gradually consumed as they supply cells for longitudinal growth 1,2 , but this model has never been proved. Here, using clonal genetic tracing with multicolour reporters and functional perturbations, we demonstrate that longitudinal growth during the fetal and neonatal periods involves depletion of chondroprogenitors, whereas later in life, coinciding with the formation of the secondary ossification centre, chondroprogenitors acquire the capacity for self-renewal, resulting in the formation of large, stable monoclonal columns of chondrocytes. Simultaneously, chondroprogenitors begin to express stem cell markers and undergo symmetric celldivision. Regulation of the pool of self-renewing progenitors involves the hedgehog and mammalian target of rapamycin complex 1 (mTORC1) signalling pathways. Our findings indicate that a stem cell niche develops postnatally in the epiphyseal growth plate, which provides a continuous supply of chondrocytes over a prolonged period.</p>
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30.
  • Nielsen, Jens B, 1962- (författare)
  • METABOLISM: A stress-coping strategy for yeast cells
  • 2019
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 572:7768, s. 184-185
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • Stressed yeast cells take up the amino acid lysine and reprogram their metabolism to free up supplies of a stress-relieving molecule. Lysine uptake therefore increases the tolerance of yeast cells to stress. See LETTER P.249
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