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961.
The effects of long-term elevated UV-B on the growth and phenolics of field-grown silver birch (Betula pendula) 总被引:2,自引:0,他引:2
The effects of long‐term elevated UV‐B radiation on silver birch (Betula pendula Roth) seedlings were studied over three growing seasons in an outdoor experiment in Finland started 64 days after germination. One group of seedlings was exposed to a constant 50% increase in UV‐BCIE radiation, which corresponds to 20–25% of ozone depletion; another group received a small increase in UV‐A radiation and a third (the control group) received ambient solar radiation. Changes in growth appeared during the third growing season; the stems of the UV‐B treated seedlings were thinner and their height tended to be shorter compared with that of the control seedlings. In contrast, there were no UV‐B effects on biomass, bud burst, bud dry weights, leaf area, rust frequency index or chlorophyll concentrations in any of the summers. During the three‐year study, the flavonols were significantly increased by the elevated UV‐B only in the first growing season. The responses varied greatly among individual compounds; the most induced were the quercetin glycosides, while the main flavonols, myricetins, were reduced by the UV‐A control treatment. In the second summer phenolic acids, such as 3,4′‐dihydroxypropiophenone‐3‐glucoside, neochlorogenic acid and 5‐coumarylquinic acid, were increased by the UV‐B treatment. In the third year, the constitutive concentrations of phenolics were not affected by the UV‐B treatment. 相似文献
962.
963.
Juan Carlos Berrío Arnoud Boom Pedro José Botero Luisa Fernanda Herrera Henry Hooghiemstra Freddy Romero Gustavo Sarmiento 《Vegetation History and Archaeobotany》2001,10(3):161-174
An environmental reconstruction of the last 10,000 14C years of a frequently flooded wetland ecosystem in the lower Magdalena valley in northern Colombia is presented, on the
basis of a multi-disciplinary study of the sediments of the upper 15 m of the core from Boquillas (74°33'E, 9°7'N; 20 m a.
s. l.). We used the following studies: pollen, lithology, organic structures, clay mineralogy, soil and sediment geochemistry,
and δ13C values. The chronology is based on 13 AMS radiocarbon dates; the humic acid fractions were used in the case of seven samples.
Pollen from local origin (swamps, open grass-rich vegetation, and gallery forest) show the development of the wetland area.
River-transported pollen from a greater distance (dry forest, montane forest, Alnus) show changes in river activity and reflect large-scale changes of climatic conditions in the Momposina basin. From c. 10,010
to 9370 uncal B. P. (zone BQS-Ia) the river system was of high energy, as inferred by the lithological changes. The landscape
was dominated by open grass-rich vegetation with gallery forest along the streams. A marked representation of Alnus and montane forest taxa indicate significant water transport and river dynamics. Climatic conditions were dry. From c. 9370-8430
uncal B. P. (zone BQS-Ib) wetlands were isolated from the main river system, and clayey sediments with kaolinite, smectite
and illite as the main minerals accumulated in a lower-energy environment. Climatic conditions were dry and changes in the
seasonal precipitation favoured the expansion of the gallery forest. From c. 8430 to 8040 uncal B. P. (zone BQS-Ic) low values
of river-transported pollen indicate dry climatic conditions and open vegetation became more abundant. The flooding frequency
of the Boquillas site diminished. From 8040 to 4900 uncal B. P. (zone BQS-Id) the Boquillas site was dominated by open vegetation
with patches of gallery forest along the streams. Supply of river-transported allochthonous pollen (from many sources) was
minimal. Clay minerals from the sediments suggest variable temperature and precipitation. From c. 4900 to 1550 uncal B. P.
)zone BQS-II) the site was within the reach of the main river system as is the case today. Frequent flooding, coinciding with
peaks of river-transported grains of Alnus and high sediment supply, point to high precipitation in the composite catchment area of the Magdalena, Cauca, San Jorge,
and Cesár rivers. High values of phosphorous in the upper part of the core point to the presence of a pre-Hispanic civilization,
approximately from 2000 uncal B. P. onward. Construction of an extensive drainage system allowed irrigation as well as drainage
depending the annual cycle of precipitation. The landscape was significantly modified and allowed an extensive crop production
on a system of raised fields.
Received May 18, 2001 / Accepted June 15, 2001 相似文献
964.
The effects of lateral far-red light (FR) and nutrient supply on the growth and nitrogen accumulation of silver birch (Betula pendula) seedlings were studied with the objective of testing the following hypotheses: (1) silver birch seedlings grow taller in response to increased FR irradiance received from the side; (2) this response is modulated by the nutritional status of the seedlings; and (3) an increase in lateral FR irradiance, and concomitant decrease in red to far-red photon ratio, affects the carbon and nitrogen economies of the seedlings. Two factorial experiments, each with two levels of mineral nutrient availability and two light treatments (background 'white' light with and without additional lateral FR simulating light reflected by neighbours in a sparse canopy) were done with small seedlings. The two experiments differed in PAR irradiance. The results of these experiments were that (1) stem elongation rate was increased by lateral FR addition, (2) there was no interaction between this effect and the nutritional status of the seedlings, and (3) neither whole plant accumulation of nitrogen nor dry weight increment was affected by lateral FR under either mineral nutrient supply regime. 相似文献
965.
Pedro M. Matias Cláudio M. Soares Lígia M. Saraiva Ricardo Coelho José Morais Jean Le Gall Maria Arménia Carrondo 《Journal of biological inorganic chemistry》2001,6(1):63-81
The primary and three-dimensional structures of a [NiFe] hydrogenase isolated from D. desulfitricans ATCC 27774 were determined, by nucleotide analysis and single-crystal X-ray crystallography. The three-dimensional structural model was refined to R=0.167 and Rfree=0.223 using data to 1.8 A resolution. Two unique structural features are observed: the [4Fe-4S] cluster nearest the [NiFe] centre has been modified [4Fe-3S-3O] by loss of one sulfur atom and inclusion of three oxygen atoms; a three-fold disorder was observed for Cys536 which binds to the nickel atom in the [NiFe] centre. Also, the bridging sulfur atom that caps the active site was found to have partial occupancy, thus corresponding to a partly activated enzyme. These structural features may have biological relevance. In particular, the two less-populated rotamers of Cys536 may be involved in the activation process of the enzyme, as well as in the catalytic cycle. Molecular modelling studies were carried out on the interaction between this [NiFe] hydrogenase and its physiological partner, the tetrahaem cytochrome c3 from the same organism. The lowest energy docking solutions were found to correspond to an interaction between the haem IV region in tetrahaem cytochrome c3 with the distal [4Fe-4S] cluster in [NiFe] hydrogenase. This interaction should correspond to efficient electron transfer and be physiologically relevant, given the proximity of the two redox centres and the fact that electron transfer decay coupling calculations show high coupling values and a short electron transfer pathway. On the other hand, other docking solutions have been found that, despite showing low electron transfer efficiency, may give clues on possible proton transfer mechanisms between the two molecules. 相似文献
966.
We demonstrate that an external constant electric field is able to modify the secondary structure of a protein and induce a transition from a β-sheet into a helix-like conformation. This dramatic change is driven by a global rearrangement of the dipole moments at the amide planes. We also predict electric-field-induced modifications of the intermediate states of the protein. 相似文献
967.
968.
Pedro J. Alcolea Ana Alonso Francisco García-Tabares Alfredo Tora?o Vicente Larraga 《PloS one》2014,9(12)
The life cycle of the trypanosomatid Crithidia fasciculata is monogenetic, as the unique hosts of these parasites are different species of culicids. The comparison of these non-pathogenic microorganisms evolutionary close to other species of trypanosomatids that develop digenetic life cycles and cause chronic severe sickness to millions of people worldwide is of outstanding interest. A ground-breaking analysis of differential protein abundance in Crithidia fasciculata is reported herein. The comparison of the outcome with previous gene expression profiling studies developed in the related human pathogens of the genus Leishmania has revealed substantial differences between the motile stages of these closely related organisms in abundance of proteins involved in catabolism, redox homeostasis, intracellular signalling, and gene expression regulation. As L. major and L. infantum agglutinate with peanut lectin and non-agglutinating parasites are more infective, the agglutination properties were evaluated in C. fasciculata. The result is that choanomastigotes are able to agglutinate with peanut lectin and a non-agglutinating subpopulation can be also isolated. As a difference with L. infantum, the non-agglutinating subpopulation over-expresses the whole machinery for maintenance of redox homeostasis and the translation factors eIF5a, EF1α and EF2, what suggests a relationship between the lack of agglutination and a differentiation process. 相似文献
969.
970.