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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 1 (1972), S. 249-257 
    ISSN: 1432-1432
    Keywords: Prebiotic ; Nucleosides ; Dry-phase ; Seawater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The purine nucleosides (adenosine, guanosine, inosine, xanthosine) are formed when the corresponding purine bases and D-ribose are heated together in the presence of certain salts and minerals. The salts remaining after the evaporation of seawater are particularly effective in these syntheses. The relevance of these reactions for prebiological evolution is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Canopies ; Competition ; Light quality ; Photosynthate partitioning ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Seedlings of shade-intolerant species react to alterations of the light climate caused by their neighbors with morphological changes that may influence the pattern of resource acquisition and utilization at the whole-canopy level. One such change, the increased stem elongation rate that is triggered by low red (R, 660 nm) to far-red (FR, 730 nm) ratios (R:FR) in dense canopies, might reduce the amount of assimilates available for leaf area expansion or root growth, and in that way affect resource capture by the canopy. We have tested this hypothesis by comparing the growth of both isolated individuals and canopies of the weed Amaranthus quitensis under conditions differing only in the spectral distribution of the incident light. When canopies received the full spectrum of sunlight, the stems were a large proportion (40–57%) of total biomass. Filtering the FR waveband (and hence raising the R:FR ratio to eliminate the neighbors' proximity-signal) resulted in shorter canopies with lighter stems. However, the growth of leaves and roots was not promoted by this treatment, indicating that the opportunity cost of the assimilates invested in the stems was nil or very small. Filtering the FR had no effect on biomass accumulation when plants were grown as isolated individuals. The higher growth of the canopics under full spectrum could be due to a higher light interception or to a higher efficiency of light conversion into biomass. The first possibility is weakened by the observation that filtering the FR had no effect on the dynamics of soil covering by the crops. The second is indirectly strengthened by results of an experiment with isolated plants showing that stem elongation, stem growth, and total plant biomass can be increased by reducing the flux of R light received by the stems without affecting the light climate of the leaves. Further work is needed to distinguish between these two possibilities; whatever the cause, our results show that the elongation responses to decreased R:FR may lead to a net increase in canopy productivity, and do not necessarily have a negative impact on the growth of resource-harvesting organs.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1939
    Keywords: Datura ferox ; Plant density ; Neighbour detection ; Canopy microclimate ; Light quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We studied the effects of density on the dynamics of seedling growth and canopy microclimate within experimental stands composed of Datura ferox L. seedlings grown in individual pots. Interception of photosynthetically active radiation (PAR) by seedlings was evaluated either indirectly, by measuring leaf area, proportion of leaf area shaded by neighbouring individuals and laminar orientation with respect to sunlight, or directly, by measuring PAR at individual leaves at their natural angle of display. An integrating cylinder, with a geometry approximating that of a stem, was used within the canopies to measure the red:far-red (R:FR) ratio of the light flux from all compass points parallel to the soil surface. Seedlings responded rapidly (i.e. 1–2 weeks) to increased density by producing longer internodes and partitioning more dry matter to stems relative to leaves. These responses were observed before either PAR interception of growth rate were reduced by the presence of neighbours. Conversely, morphogenetic adjustment was preceded by a consistent effect of plant density on the R:FR ratio of the light received by the integrating cylinder. Air and soil temperature were not affected by density in these experiments. Differences in wind velocity within the canopy associated with plant density were avoided by the experimental procedure. The results support the idea that the drop in R:FR ratio of the light flux parallel to the ground — e.g. reflected sunlight — is an early signal that allows rapid adjustment of plant form to changes in canopy structure.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 27 (1971), S. 1234-1237 
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Resumen Sobre la base del efecto de irradiaciones de baja energía con luz rojo lejana, y la reversión del mismo por la luz roja, se postula la participación del fitocromo en el control de la forma de la hoja deTaraxacum officinale.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archives of environmental contamination and toxicology 34 (1998), S. 128-135 
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract. The effects of different concentrations of Hg, Cd, and Pb on cell growth, oxygen consumption, and production and contents of chlorophyll a and b of Z and B strains of Euglena gracilis was studied. Cell uptake of Cd and Pb was also determined. A greater cell density reached in the presence of Cd2+ correlated with a lower metal uptake capacity in B-strain cells. Cells of Z strain, preexposed to low concentrations of either Hg2+ (1.5 μM) or Cd2+ (50 μM) for several generations showed improved heavy metal tolerance (greater cell density and viability) together with similar metal uptake capacity. Because Cd2+ preadaptation but not Hg2+ pretreatment induced a significant increase in the content of acid-soluble thiols, the data suggest the existence of different mechanisms of heavy metal detoxification in Euglena. The fact that Z-strain cells showed a greater Cd2+ uptake under all the conditions assayed suggests that Z strain would be more suitable for bioremediation of polluted waters.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 47 (1991), S. 616-619 
    ISSN: 1420-9071
    Keywords: Flavonoids ; glutathione S-transferase ; quercetin ; rat liver cytosol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The inhibitory potencies of different flavonoids for rat liver cytosolic glutathione S-transferase activity varied over 30-fold, depending on the pattern of hydroxylation, the presence of a C-2, C-3 double bond and the substitution of a hydroxyl group with a sugar moiety. Kinetic inactivation studies of the enzyme with the inhibitor quercetin revealed a non-competitive profile versus both glutathione and 1-chloro-2,4-dinitrobenzene.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 28 (1972), S. 364-364 
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Résumé La qualité de la lumière a modifié le passage de l'eau dans les cellules épidermiques des pétioles deTaraxacum officinale. L'irradiation par du rouge sombre a augmenté la rapidité avec laquelle l'eau entre dans la cellule et la lumière rouge clair a renversé cet effet.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Helgoland marine research 49 (1995), S. 467-487 
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A detailed analysis is presented of the main contributions, both local and international, to the fields of oceanography and fishery sciences resulting from exploratory cruises carried out on the continental shelf off Argentina over the last 100 years. The end of the 19th century is chosen as a starting point for this analysis as it marks the beginning of active marine research by Argentinian scientists and an accumulation of information on Antarctic and Subantarctic organisms in foreign journals. Mention is also made of previous contributions derived from the classic expeditions and global circumnavigational voyages during the 18th and 19th centuries. Although the aims of those were not always strictly oceanographic, they rendered significant information to this field of knowledge. In the early years, references arose mainly from the particular geographic situation of the Argentinian shelf, a necessary passage in the navigation routes to the Pacific Ocean, and later on the way to Antarctica. Sources of information are divided into four categories: (a) foreign scientific projects in the area; (b) investigation by Argentinian scientists and research vessels; (c) joint projects between Argentinian and foreign institutions; and (d) contributions from sources other than oceanographic cruises (commercial navigation, maritime weather reports, satellite images, etc.). The analysis includes an updated and classified bibliographical list of the main contributions to the fields of oceanography and fishery sciences derived from those sources, published either in international or local journals or appearing as technical and internal reports. The motivations, objectives and main achievements of foreign surveys and programmes in the area and their impact on local scientific progress are discussed. The early sixties mark a turning point in the evolution of international research in the area. The creation of biological stations along the Argentinian coast, and the support given to the pooling of human resources set the basis for the development of bilateral programmes. Similar progress in Brazil and Uruguay led to the outgrowth of regional activities. Joint scientific efforts described in this analysis include the programmes carried out by the research vessels of Germany (“Walther Herwig”, “Meteor”), Japan (“Kaiyo Maru”, “Orient Maru”, “Shinkai Maru”), Poland (“Professor Siedlecki”), Russia (“Evrika”, “Dimitry Stefanov”) and the USA (“Vema”, “Atlantis II”), the achievements of which are a landmark in the evolution of marine science in the aea.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 41 (1998), S. 1-5 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Linear, low molecular weight poly(2-furyl)methylene sulfide was obtained bubbling hydrogen sulfide by through aqueous furfuraldehyde solutions. The product was soluble in chloroform and acetone. Characterization was carried out by elemental analysis, IR, NMR 1H and 13C (DEPT) techniques. Evidence for the presence of OH and SH terminal groups was found. This fact points to a plausible mechanism through the initial formation of unstable α-hydroxythiols. A scheme for the polymerization mechanism is offered.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    GeoJournal 7 (1983), S. 229-246 
    ISSN: 1572-9893
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography
    Notes: Abstract The oil discoveries in Southern Mexico are now thought to be linked in one vast field a geological blessing that could catapult Mexico as the world's second largest oil producer. However, after six years of oil boom it is now clear that this does not mean, by itself, a blessing for Mexico. Current experience leaves no doubt that Mexico's problems can not be solved only by oil exports. Initially, oil was the ‘key of development’ that the government had envisioned. Rapid economic growth created almost four million jobs in five years. The sharp rise in oil prices in 1980 brought in far larger revenues as expected and the government launched an expensive industrialization programme and overspent. Nevertheless, Mexico ran into problems in 1981 when worldwide demand for oil began to fall. By that time Mexico had lost many of its costumers and an estimated $10 thousand million in total revenues. The slump in worldwide oil demand damaged Mexico's ambitious development plan. Because solutions to the country's troubles hinge on economic recovery, the government has already taken some pragmatic steps to shore up the slumping economy. The government haltered refinery expansion and public works projects even in the oil industry. However, its most immediate problem, its huge foreign debt owned mostly to American lenders, leaves little space for optimism. The initial recovery period will take at least 18 months. What went wrong? How could Mexico fall into its worst financial crisis in spite of the oil revenues?
    Type of Medium: Electronic Resource
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