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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 21 (1993), S. 393-401 
    ISSN: 1432-1017
    Keywords: NMR ; β-sheets ; α-helices ; dynamics ; protein-actions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The results of NMR studies using several nuclei indicate that proteins have considerable internal mobility. The most obvious is the mobility of side-chains. This mobility is general on the exterior surfaces but extends internally in a differential way. The functional value of surface mobility concerns both on and off rates of ligand binding (e.g. metal ions and parts of substrates) and protein/protein interactions. The mobility, which indicates that recognition is more in the hand-in-glove class than in the lock-in-key class, makes for a modified view of the specificity of protein interactions. Thus, fast on/off systems cannot be as selective as slower systems. Segmental mobility of proteins is considered in the context of protein secondary structure. The least mobile segments are the β-sheet and the tight β-turn. Mobility is always possible for, but not within, rod-like helices and in loose turns. Many examples are given and the importance of mobility in molecular machines is described. Finally, examples are given of virtually random-coil proteins, segments, and linker regions between domains and the functional value of such extremely dynamic regions of proteins is discussed.
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  • 2
    ISSN: 1420-9071
    Keywords: Morphogenesis and inorganic crystals ; crystal morphology ; amorphous solids ; membrane enzymes ; tubulins ; filamentous structures ; equilibrium growth ; crystals ; acantharia ; radiolaria ; desmids ; loxodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We consider morphogenesis with special references to the development of mineral frameworks, organic filamentous structures and the location of enzymes, including ion-pumps, in membranes. Starting from a description of the morphology of inorganic crystals we analyse so-called equilibrium growth, i.e. growth at constant shape, both outside and inside biological systems. It is shown that an initial small spherical cell in which linear, ordered, inorganic or organic features are built will become distorted. The distortion is due to stresses which affect membrane curvature and consequently rearrange enzymes in membranes. The cell system can rapidly attain a steady-state of development, (‘equilibrium’) growth, of fixed morphology. After a considerable growth period the cell may cease to grow or the steady state may be broken and a transition can then occur to a quite new morphology. Examples are taken mostly from unicellular organisms but the ideas apply to multi-cellular systems.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 27 (1987), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Seeds of Poa trivialis L. were collected from one grassland and two arable habitats. Seeds from the grassland population were less dormant than the arable populations. Distal (upper) seeds were consistently more dormant than proximal (basal) seeds. Dry storage at 4°C and 15°C for 4 weeks after shedding resulted in a slightly greater loss of dormancy than storage at 23°C. Germination was enhanced by subjecting seeds stored at 15°C to repeated hydration and dehydration cycles. Germination of P. trivialis seeds was density-dependent. Germination of distal seeds was particularly impaired at high densities. The ecological implications of these results are discussed in relation to seed survival strategies.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 32 (1983), S. 0 
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In field and screenhouse experiments, pollination of inflorescences of three pearl millet F1 hybrids and two male-sterile (ms) lines with fresh viable pollen 5–8 days after inoculation with a Tolyposporium penicillariae sporidial suspension reduced smut severities significantly compared with inoculated, non-pollinated control plants. Smut development was not significantly reduced in a ms line following pollination of inoculated inflorescences with pollen of low viability. The implications of these findings in developing an effective screening technique for smut resistance and in controlling this disease in pearl millet are discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Weed research 45 (2005), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Field experiments were conducted to quantify the natural levels of post-dispersal seed predation of arable weed species in spring barley and to identify the main groups of seed predators. Four arable weed species were investigated that were of high biodiversity value, yet of low to moderate competitive ability with the crop. These were Chenopodium album, Sinapis arvensis, Stellaria media and Polygonum aviculare. Exclusion treatments were used to allow selective access to dishes of seeds by different predator groups. Seed predation was highest early in the season, followed by a gradual decline in predation over the summer for all species. All species were taken by invertebrates. The activity of two phytophagous carabid genera showed significant correlations with seed predation levels. However, in general carabid activity was not related to seed predation and this is discussed in terms of the mainly polyphagous nature of many Carabid species that utilized the seed resource early in the season, but then switched to carnivory as prey populations increased. The potential relevance of post-dispersal seed predation to the development of weed management systems that maximize biological control through conservation and optimize herbicide use, is discussed.
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  • 6
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Experiments were conducted on linseed (Linum usiãissimum L.) and autumn-sown field bean (Vicia faha L.) to test how well the relative leaf area-based yield loss prediction model of Kropff & Spitters could estimate yield loss due to interference from Stellaria media L. (common chick-weed) or barley (Hordeum vulgare L.) alone or a combination of both S. media and barley. Damage coefficients were calculated for all comparisons. Generally, the model provided a better estimate of yield loss due to interference from barley than from S. media because of both the variability in crop yield response stemming from S. media's plasticity and the generally minor crop yield response to S. media interference. The addition to the model of a parameter accounting for asymptotic yield loss was, generally, not warranted for either S. media or barley in the single-weed species data sets. When both S. media and barley were present as weed species in the crop, the model that fitted the data best for six out of 10 data sets was the one in which a separate damage coefficient was included for both species. There was no evidence that the presence of S. media influenced damage coefficient values for barley. However, in the presence of barley a parameter accounting for asymptotic yield loss was warranted for S. media in the two-weed species model. The combination of the addition of this parameter and the presence or barley affected the values of the damage coefficients for S. media in the two-weed species compared with the single-weed species models. Consequently, it was shown for these two weed species that two-weed species yield loss prediction models parameterized using data from single-weed species experiments generally resulted in different estimates of yield loss in comparison with models parameterized using data from two-weed species experiments.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 27 (1987), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Weeds in a total of 450 fields of winter oilseed rape in nine areas of central southern England were surveyed, just prior to harvest during summer 1985, to identify those that had survived herbicide treatment or had not been sprayed and, thus, were capable of re-infestation or contamination of the harvested crop. Sixty-two species were identified; their levels of infestation were scored and distribution within the field noted. The most frequent species was Galium aparine, which occurred in 57% of fields. Mayweeds (Tripleurospermum inodorum, Matricaria recutita and Anthemis cotula) occurred in 23% of fields and Papaver rhoeas in 21%. All other species occurred in less than 20% of fields, the most prevalent being Sonchus asper(18%). Grassweeds were relatively infrequent, reflecting the widespread use of effective graminicides; the most prevalent was Arena spp., found in 9% of fields. Although most species were distributed throughout the field, Geranium dissection (13%) and Sisymbrium officinale (7%) were virtually confined to field margins (extending 1 m into the crop) and headlands (10m into the crop), respectively. Several species exhibited a well-defined regional distribution; Silene alba was virtually restricted to the most southern counties surveyed, whilst Papaver rhoeas and Viola arvensis were conspicuously absent from the eastern area.
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  • 8
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of reduced-cultivation Systems on weeds in cereals are reviewed. Increasing dependence of these Systems upon Chemical weed control together with changes in the soil physical environment are expected to modify existing weed floras. Annual-grass weeds are likely to remain a problem with the use of minimal cultivations, particularly when early drilling is practised, while hitherto unimportant species may become more prevalent, e.g. Bromus spp. Furthermore, reduced cultivations may encourage the establishment of wind-disseminated species. However, annual dicotyledonous species characteristic of arable land are expected to continue to decline.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Dose–response experiments were conducted in glasshouse pot experiments to investigate the selectivity of oxadiargyl, a recently introduced herbicide, in direct-seeded rice under both aerobic and anaerobic conditions. Crop sensitivity to oxadiargyl was comparatively greater for wet-seeded (anaerobic) than for dry-seeded rice (aerobic). Likewise, greater efficacy against Echinochloa crus-galli (L.) was also observed under anaerobic conditions. These results indicate greater activity of oxadiargyl under anaerobic conditions, but that application pre-sowing with subsequent flooding would reduce selectivity in wet-seeded rice. The results are discussed in relation to rice production in Mediterranean agriculture.
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  • 10
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Differential competitive ability of six winter wheat cultivars and traits that confer such attributes were investigated for a range of seed rates in the presence or absence of weeds for a naturally occurring weed flora in two successive years in split-plot field experiments. Crop height and tillering capacity were considered suitable attributes for weed suppression, although competitiveness is a relative rather than an absolute characteristic. Maris Huntsman and Maris Widgeon were the most competitive cultivars whereas Fresco was the least competitive. Manipulation of seed rate was a more reliable factor than cultivar selection for enhancement of weed suppression, although competitiveness of cultivars Buster, Riband and Maris Widgeon was not enhanced by increased seed rate. Crop densities ranging between 125 and 270 plants m−2 were found to offer adequate weed suppression. Linear relationships were observed between individual and total weed species dry weight and reproductive structures per unit area.
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