HIGHLY BRANCHED ISOPRENOID ALKENES FROM DIATOMS: A BlOSYNTHETIC AND LIFE CYCLE INVESTIGATION

In addition to the production of phytol (from chlorophylls) and sterols, a limited number of diatom species are capable of synthesising unusual C25 and C30 highly branched isoprenoid (HBl) alkenes. At the outset of the current investigation, the structures of most C25 and C30 HBIs had been identified. Some environmental factors had been shown to control their production, although a detailed understanding of these remained unclear. In addition, the biological functions of the chemicals remained unknown, and the reasons for their production by some species and not by others, was not understood. Investigations on the distributions of C25 and C30 HBl alkenes biosynthesised by Rhizosolenia setigera demonstrated a dependence on the physiological status of the cells, as measured by the position of this diatom in its life cycle. Thus, while C30 HBIs were observed at every stage of the life cycle, C25 HBIs were not always present in the cells. Since the synthesis of C25 HBIs appears to be stimulated by the onset of auxosporulation (sexual reproduction), an explanation is provided as to why they have rarely been observed in previous studies. Two novel monocyclic C30 alkenes (previously reported in other strains of Rhizosolenia setigerd), and a novel monocyclic C25 alkene were also observed during life cycle experiments. The two C30 hydrocarbons structures were subsequently characterised and the potential geochemical relevance of these compounds was highlighted by comparison of their mass spectral and chromatographic properties with those of alkenes reported in sediments and suspended water column particles. An investigation of terpenoid (including HBl) biosynthesis in the diatoms Haslea ostrearia, Rhizosolenia setigera and Pleurosigma intermeclium has been performed. Evidence for species and organelle dependent biosynthetic pathways has been observed. Phytol is synlhesised by each species investigated according to the recently discovered methyl-erythritol phosphate (MEP) pathway. This pathway is also involved in the synthesis of C25 HBIs in the two species Haslea ostrearia and Pleio-osigma intermedium. In contrast, C25 and C30 HBIs, and (at least) one monocyclic C30 alkene, appear to be made predominantly via the mevalonate (MVA) route in the diatom R. setigera. Evidence for the contribution of the MVA pathway to the biosynthesis of sterols was found for the diatoms Rhizosolenia setigera, and Pleurosigma intermedium. In contrast, only contributions from the MEP pathway were found for the biosynthesis of sterols in Haslea ostrearia. Preliminary evidence for dynamic interchange between the two pathways has also been observed. Fractionation of Rhizosolenia setigera cells revealed that phytol was present in the chloroplasts, while sterols and HBIs were present in the cytoplasm

Grounding Abstract Word Definitions In Prior Concrete Experience

Longman’s Dictionary of Contemporary English (LDOCE) and Cambridge International Dictionary of English (CIDE) have a defining vocabulary of 2000 words from which most but not all of the words are defined. We developed an algorithm, applicable to any dictionary, for recursively deleting words not used in any definition until the corpus is reduced to a subset – a grounding kernel – from which all the words of the complete dictionary are reachable by definition alone. We compared LDOCE’s and CIDE’s defining vocabulary (DV) and grounding kernel (GK) against the rest of its words, on (1) concreteness, (2) imagery and (3) age of acquisition based on the MRC psycholinguistic database [Wilson 1988]. Both GK and DV proved significantly higher on all three scales (p<0.001) for all but 2 of the 12 comparisons (no difference in concreteness in LDOCE for either GK or DV). The difference was also consistently greater using our automatically computed GK than using the DV defined by the compilers of LDOCE and CIDE

Grounding Abstract Word Definitions In Prior Concrete Experience

Longman’s Dictionary of Contemporary English (LDOCE) and Cambridge International Dictionary of English (CIDE) have a defining vocabulary of 2000 words from which most but not all of the words are defined. We developed an algorithm, applicable to any dictionary, for recursively deleting words not used in any definition until the corpus is reduced to a subset – a grounding kernel – from which all the words of the complete dictionary are reachable by definition alone. We compared LDOCE’s and CIDE’s defining vocabulary (DV) and grounding kernel (GK) against the rest of its words, on (1) concreteness, (2) imagery and (3) age of acquisition based on the MRC psycholinguistic database [Wilson 1988]. Both GK and DV proved significantly higher on all three scales (p&lt;0.001) for all but 2 of the 12 comparisons (no difference in concreteness in LDOCE for either GK or DV). The difference was also consistently greater using our automatically computed GK than using the DV defined by the compilers of LDOCE and CIDE

Migration distance from birthplace and its association with relative income and employment share among heterosexual couples in Switzerland

Among heterosexual couples, employment of the female partner may suffer from household migration often driven by the job of the male partner. Most research has traditionally focused on the distance moved after couple formation and has neglected how far partners live from their birthplaces. Recent life course research has shown that staying in, leaving or returning to the place of origin of one or both partners often reflects couples’ work-family arrangements. This study contributes to this literature by examining the division of employment between partners and their relative contribution to household income according to migration distances. We analyse data from a national sample of economically active individuals living with heterosexual partners in Switzerland. When controlling for selectivity of migrant couples, the analysis confirms that long-distance household migration benefits men’s relative earnings. Among couples who migrated within the same region, employment is more equally shared between partners than among other couples, including non-migrant couples. The relative distance to birthplaces also matters. Women’s contribution to household income is higher among couples in which men migrated close to women’s birthplace and is lower among couples where women migrated close to men’s birthplace compared to women in other couples. This study suggests that future research on household migration should consider important social ties and places beyond the ‘last family move’ and the mechanisms by which these ties and places influence couples’ decisions about where to live together and economic outcomes

Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment

International audienceThe early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations. Lithic vestiges are the only sources that remain of this process and the understanding of the material's properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment. Several models of the structural transformations upon heating have been proposed in the current literature. These models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony. In order to propose a new model, we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy, solid state NMR, X-ray diffraction and electron microscopy. The results show that the major transformation to happen is the loss of silanole (SiOH) and the creation of new Si-O-Si bonds according to the reaction: Si-OH HO-Si -> Si -O-Si + H2O. This reaction starts between 200 degrees C and 300 degrees C and causes an increase in the hardness of the rocks. The maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created H2O and depend on the size of the specimen and the volume of its porosity. These results also show that the annealing duration at maximum temperature can be relatively short (<50 min) for a sufficiently large amount of transformation to be accomplished

Learning from the past : Impact of the Arctic Oscillation on sea ice and marine productivity off northwest Greenland over the last 9,000 years

Climate warming is rapidly reshaping the Arctic cryosphere and ocean conditions, with consequences for sea ice and pelagic productivity patterns affecting the entire marine food web. To predict how ongoing changes will impact Arctic marine ecosystems, concerted effort from various disciplines is required. Here, we contribute multi-decadal reconstructions of changes in diatom production and sea-ice conditions in relation to Holocene climate and ocean conditions off northwest Greenland. Our multiproxy study includes diatoms, sea-ice biomarkers (IP(25)and HBI III) and geochemical tracers (TOC [total organic carbon], TOC:TN [total nitrogen], delta C-13, delta N-15) from a sediment core record spanning the last c. 9,000 years. Our results suggest that the balance between the outflow of polar water from the Arctic, and input of Atlantic water from the Irminger Current into the West Greenland Current is a key factor in controlling sea-ice conditions, and both diatom phenology and production in northeastern Baffin Bay. Our proxy record notably shows that changes in sea-surface conditions initially forced by Neoglacial cooling were dynamically amplified by the shift in the dominant phase of the Arctic Oscillation (AO) mode that occurred at c. 3,000 yr BP, and caused drastic changes in community composition and a decline in diatom production at the study site. In the future, with projected dominant-positive AO conditions favored by Arctic warming, increased water column stratification may counteract the positive effect of a longer open-water growth season and negatively impact diatom production.Peer reviewe

Sea ice and primary production proxies in surface sediments from a High Arctic Greenland fjord : Spatial distribution and implications for palaeoenvironmental studies

In order to establish a baseline for proxy-based reconstructions for the Young Sound-Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP25 was detected at all sites but at low concentrations, indicating that IP25 records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate.Peer reviewe

An Ultra-High Resolution Sediment Record of Deglacial and Holocene Climate Change in East Antarctica: IODP Exp 318 Hole 1357 – The Adélie Basin

第3回極域科学シンポジウム　横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月27日（火） 国立国語研究所 ２階講