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  • 1
    Electronic Resource
    Electronic Resource
    Free-radical-induced mutation vs redox regulation: Costs and benefits of genes in organelles (1996)
    Springer
    Journal of molecular evolution 42 (1996), S. 482-492 
    Details
    ISSN: 1432-1432
    Keywords: Aging ; Chloroplasts ; Mitochondria ; Cell evolution ; Cytoplasmic genomes ; Gene transfer ; Redox regulation ; Free radical mutagenesis ; Nitrogen fixation ; Endosymbiosis ; Mutation frequency ; Uniparental inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The prokaryotic endosymbionts that became plastids and mitochondria contained genes destined for one of three fates. Genes required for free-living existence were lost. Most genes useful to the symbiosis were transferred to the nucleus of the host. Some genes, a small minority, were retained within the organelle. Here we suggest that a selective advantage of movement of genes to the nucleus is decreased mutation: plastids and mitochondria have high volume-specific rates of redox reactions, producing oxygen free radicals that chemically modify DNA. These mutations lead to synthesis of modified electron carriers that in turn generate more mutagenic free radicals—the “vicious circle” theory of aging. Transfer of genes to the nucleus is also advantageous in facilitating sexual recombination and DNA repair. For genes encoding certain key components of photosynthesis and respiration, direct control of gene expression by redox state of electron carriers may be required to minimize free radical production, providing a selective advantage of organelle location which outweighs that of location in the nucleus. A previous proposal for transfer of genes to the nucleus is an economy of resources in having a single genome and a single apparatus for gene expression, but this argument fails if any organellar gene is retained. A previous proposal for the retention of genes within organelles is that certain proteins are organelle-encoded because they cannot be imported, but there is now evidence against this view. Decreased free radical mutagenesis and increased sexual recombination upon transfer to the nucleus together with redox control of gene expression in organelles may now account for the slightly different gene distributions among nuclei, plastids, and mitochondria found in major eukaryote taxa. This analysis suggests a novel reason for uniparental inheritance of organelles and the evolution of anisogametic sex, and may also account for the occurrence of nitrogen fixation in symbionts rather than in nitrogen-fixing organelles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02352278
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  • 2
    Electronic Resource
    Electronic Resource
    Does prey dispersion affect frequency-dependent predation by wild birds? (1997)
    Springer
    Oecologia 111 (1997), S. 292-296 
    Details
    ISSN: 1432-1939
    Keywords: Key words Frequency dependence ; Selective predation ; Bird ; Dispersion ; Density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Despite the fact that the vast majority of natural prey items are dispersed in a non-random manner, few studies of frequency-dependent selective predation have explicitly examined the effect of prey dispersion on selectivity. We examined the effect of prey dispersion on the direction and strength of frequency-dependent selection by wild birds feeding on artificial prey (green or brown pastry baits). In a series of four experimental manipulations, we tested for the occurrence of frequency dependence with two different dispersion patterns (random or clumped). Manipulations were carried out at one of two absolute densities (25 prey m−2 or 100 prey m−2), and were repeated at different sites in Southampton, England and Aljarafe, Spain. Our results suggest that prey dispersion has no effect on either frequency-dependent or -independent preferences. One possible explanation for this is that the birds had virtually complete information about prey frequencies at the relatively high densities used and based their preferences on their overall perception of availability. However, we cannot rule out the possibility that dispersion may influence selectivity when prey are cryptic or available at lower absolute densities. Although there was no effect of dispersion, frequency-dependent selection was, overall, significantly anti-apostatic (i.e. rare baits were more preferred than common baits). This anti-apostatic effect was stronger in Southampton than Aljarafe and stronger at 100 prey m−2 than 25 prey m−2. The differences in the strength of selection between the two locations was interpreted in terms of (i) whether the avian predators foraged in flocks or not, and (ii) the number of different species present (and, consequently, the variation in preference among individual birds).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050237
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of relative plant density and floral morphological complexity on the behaviour of bumblebees (1998)
    Springer
    Oecologia 117 (1998), S. 543-550 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsBombus spp. ; Foraging ; Pollination ; Resource utilisation ; Visitation rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We assessed the combined effects of varying the relative density and the relative floral morphological complexity of plant species on the behaviour of their bumblebee pollinators. Three species of bumblebee (Bombus pascuorum, B. terrestris and B. hortorum) were observed foraging on experimental arrays consisting of pair-wise combinations of four plant species: Borago officinalis, Phacelia tanacetifolia (both with simple flowers), Antirrhinum majus and Linaria vulgaris (both with complex flowers). Plant arrangements consisted of either two simple-flower species, a simple with a complex species or two complex species. The number of plants in each array was constant, while the frequency of each species was manipulated so that it was either rare, equal or common compared with its competitor. Contrary to predictions, rare plants were actually at an advantage in terms of the number of bees attracted per plant. However, rare plants were at a disadvantage in terms of pollen wastage because foragers more often went to a flower of another species after visiting a rare plant. The behaviour of bees on each plant species was further affected by plant floral complexity and the identity of the other species in the array. The three bumblebee species were markedly different in their foraging behaviour and in their responses to varying floral density and complexity. Each species preferred particular flower species. The results are discussed with reference to resource partitioning among bumblebee species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050691
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  • 4
    Electronic Resource
    Electronic Resource
    Floral display size in comfrey, Symphytum officinale L. (Boraginaceae): relationships with visitation by three bumblebee species and subsequent seed set (1998)
    Springer
    Oecologia 113 (1998), S. 502-508 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsBombus spp. ; Foraging ; Comfrey ; Floral display ; Seed set
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The fecundity of insect-pollinated plants may not be linearly related to the number of flowers produced, since floral display will influence pollinator foraging patterns. We may expect more visits to plants with more flowers, but do these large plants receive more or fewer visits per flower than small plants? Do all pollinator species respond in the same way? We would also expect foragers to move less between plants when the number of flowers per plant are large, which may reduce cross-pollination compared to plants with few flowers. We examine the relationships between numbers of inflorescence per plant, bumblebee foraging behaviour and seed set in comfrey, Symphytum officinale, a self-incompatible perennial herb. Bumblebee species differed in their response to the size of floral display. More individuals of Bombus pratorum and the nectar-robbing B.␣terrestris were attracted to plants with larger floral displays, but B. pascuorum exhibited no increase in recruitment according to display size. Once attracted, all bee species visited more inflorescences per plant on plants with more inflorescences. Overall the visitation rate per inflorescence and seed set per flower was independent of the number of inflorescences per plant. Variation in seed set was not explained by the numbers of bumblebees attracted or by the number of inflorescences they visited for any bee species. However, the mean seed set per flower (1.18) was far below the maximum possible (4 per flower). We suggest that in this system seed set is not limited by pollination but by other factors, possibly nutritional resources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050402
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  • 5
    Electronic Resource
    Electronic Resource
    Benign methylmalonic acidemia in a sibship with distal renal tubular acidosis (1998)
    Springer
    Pediatric nephrology 12 (1998), S. 564-566 
    Details
    ISSN: 1432-198X
    Keywords: Key words: Methylmalonic acidemia ; Distal renal tubular acidosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Two male infants born to consanguineous parents were investigated for feeding difficulties in the 1st month of life. Both were found to have distal renal tubular acidosis (dRTA) with hypercalciuria. Nephrocalcinosis was present in the first child but not in the second. Urinary organic acid profile demonstrated an excess of methylmalonic acid (MMA) in both children in the absence of any other organic acid. MMA mutase activity and propionate incorporation were normal. There have been no neurological symptoms in either child. The first child has normal growth and psychomotor development at 4 years. His brother, who also has significant gastro-oesophageal reflux, has failed to thrive and currently requires nasogastric feeding and caloric supplements to maintain weight along the 3rd percentile. Urinary and plasma MMA continue to be raised in both cases. The association of increased urinary and plasma MMA and dRTA presenting in the 1st month of life has not previously been reported and may represent a new syndrome of autosomal recessive inheritance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004670050505
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  • 6
    Electronic Resource
    Electronic Resource
    Protein synthesis by isolated pea mitochondria is dependent on the activity of respiratory complex II (1998)
    Springer
    Current genetics 33 (1998), S. 320-329 
    Details
    ISSN: 1432-0983
    Keywords: Key words Mitochondria ; Protein synthesis ; Succinate dehydrogenase ; Regulation of gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In isolated pea (Pisum sativum L.) mitochondria incorporation of 35S-methionine into newly synthesised proteins was influenced by the presence of site-specific inhibitors of the respiratory electron-transport chain. These effects were not produced by changes in the rate of respiratory electron transport itself nor by changes in ATP concentration. Protein synthesis was inhibited by inhibitors of ubiquinone reduction but not by inhibitors of ubiquinol oxidation. By the use of additional inhibitors at specific sites of the respiratory chain, different oxidation-reduction states were obtained for the different complexes in the electron-transport chain. It was found that electron transport through succinate:ubiquinone oxidoreductase (respiratory complex II) was specifically required for protein synthesis, even when all the other conditions for protein synthesis were satisfied. We suggest that a subunit of complex II, or a component closely associated with complex II, is involved in a regulatory system that couples electron transport to protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002940050343
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  • 7
    Electronic Resource
    Electronic Resource
    Advances in development of medications for alcoholism treatment (1998)
    Springer
    Psychopharmacology 139 (1998), S. 20-33 
    Details
    ISSN: 1432-2072
    Keywords: Key words Pharmacotherapy ; Medications ; Craving ; Comorbidity ; Depression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Over the past decade, research on medications to treat alcohol problem has flourished. Naltrexone and acamprosate are tangible fruits of such endeavors and each has now earned approval in a large number of countries. Recent studies on naltrexone indicate that patient compliance is important if full benefits are to be achieved. Several laboratory studies with human subjects are beginning to elucidate the mechanisms underlying efficacy of naltrexone, as well as explaining variability of response among subpopulations of drinkers. In addition to these two agents, recent investigations have also demonstrated that the antidepressants desipramine, imipramine, and fluoxetine reduce mood-related symptoms and, to some extent, drinking itself in alcoholics who are depressed. Research to date suggests that opioid antagonists and selective serotonin reuptake inhibitors are more effective in reducing alcohol intake when used in combination. Clinical issues, methodology, and directions for future research are also reviewed in this article. In particular, issues addressed include alternative dosage regimens, necessary duration of treatment, employment of medications in combination, integration of pharmacologic agents with behavioral interventions, enhancement of patient compliance, and concurrent treatment of psychiatric comorbidity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002130050686
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  • 8
    Electronic Resource
    Electronic Resource
    Repellent scent-marking of flowers by a guild of foraging bumblebees (Bombus spp.) (1998)
    Springer
    Behavioral ecology and sociobiology 43 (1998), S. 317-326 
    Details
    ISSN: 1432-0762
    Keywords: Key words Tarsal secretion ; Floral rewards ; Pheromone ; Symphytum officinale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have found that foraging bumblebees (Bombus hortorum, B. pascuorum, B. pratorum and B.␣terrestris) not only avoid flowers of Symphytum officinale that have recently been visited by conspecifics but also those that have been recently visited by heterospecifics. We propose that the decision whether to reject or accept a flower is influenced by a chemical odour that is left on the corolla by a forager, which temporarily repels subsequent foragers. Honeybees and carpenter bees have previously been shown to use similar repellent forage-marking scents. We found that flowers were repellent to other bumblebee foragers for approximately 20 min and also that after this time nectar levels in S. officinale flowers had largely replenished. Thus bumblebees could forage more efficiently by avoiding flowers with low rewards. Flowers to which extracts of tarsal components were applied were more often rejected by wild B. terrestris workers than flowers that had head extracts applied, which in turn were more often rejected than flowers that had body extracts applied. Extracts from four Bombus species were equally repellent to foragers. The sites of production of the repellent scent and its evolutionary origins are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002650050497
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  • 9
    Electronic Resource
    Electronic Resource
    Complex formation in plant thylakoid membranes. Competition studies on membrane protein interactions using synthetic peptide fragments (1995)
    Springer
    Photosynthesis research 44 (1995), S. 277-285 
    Details
    ISSN: 1573-5079
    Keywords: light harvesting complex II ; membrane proteins ; macromolecular recognition ; protein phosphorylation ; excitation energy transfer ; energy quenching ; psb H
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thylakoid membranes of pea were used to study competition between extra-membrane fragments and their parental membrane-bound proteins. Phosphorylated and unphosphorylated fragments of light harvesting complex II (LHC II) from higher plants were used to compete with LHC II for interactions with itself and with other thylakoid protein complexes. Effects of these peptide fragments of LHC II and of control peptides were followed by 80 K chlorophyll fluorescence spectroscopy of isolated thylakoids. The phosphorylated LHC II fragment competes with membrane-bound phosphoproteins in the phosphatase reaction. The same fragment accelerates the process of dark-to-light adaptation and decreases the rate of the light-to-dark adaptation when these are followed by fluorescence spectroscopy. In contrast, the non-phosphorylated LHC II peptide does not affect the rate of adaptation but produces results consistent with inhibition of formation of a quenching complex. In this quenching complex we propose that LHC II remains inaccessible to the LHC II kinase, explaining an observed decrease in LHC II phosphorylation in the later stages of the time-course of phosphorylation. The most conspicuous protein which is steadily phosphorylated during the time-course of phosphorylation is the 9 kDa (psbH) protein. The participation of the phosphorylated form of psbH in the quenching complex, where it is inaccessible to the phosphatase, may explain its anomalously slow dephosphorylation. The significance of the proposed complex of LHC II with phospho-psbH is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00048601
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