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  • Articles  (158)
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  • 1995-1999  (158)
  • Biology  (151)
  • Natural Sciences in General  (18)
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  • Articles  (158)
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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 27 (1996), S. 111-133 
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Resource polymorphism in vertebrates is generally underappreciated as a diversifying force and is probably more common than is currently recognized. Research across diverse taxa suggest they may play important roles in population divergence and speciation. They may involve various kinds of traits, including morphological and behavioral traits and those related to life history. Many of the evolutionary, ecological, and genetic mechanisms producing and maintaining resource polymorphisms are similar among phylogenetically distinct species. Although further studies are needed, the genetic basis may be simple, in some cases under the control of a single locus, with phenotypic plasticity playing a proximate role in some taxa. Divergent selection including either directional, disruptive, or frequency-dependent selection is important in their evolution. Generally, the invasion of "open" niches or underutilized resources requiring unique trophic characters and decreased interspecific competition have promoted the evolution of resource polymorphisms. Further investigations centered on their role in speciation, especially adaptive radiation, are likely to be fruitful.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Treatment with supplementary UV-B resulted in decreases in transcripts of the photosynthetic genes Lhcb and psbA and concomitant increase in transcripts of two pathogen-related genes, PR-1 and PDF1·2, in Arabidopsis thaliana. UV-B exposure caused increases in jasmonic acid (JA) levels and ethylene production. UV-B treatment of jar1 and etr1-1 mutants, which are insensitive to JA and ethylene, respectively, showed that the increase in PR-1 transcripts was dependent on ethylene and PDF1·2 transcripts on both JA and ethylene. In contrast, the down-regulation of photosynthetic transcripts was independent of both compounds. Previous studies have indicated a role for reactive oxygen species (ROS) in the UV-B-induced down-regulation of the photosynthetic genes and up-regulation of PR-1 genes. Here we have shown that ROS are also required for the UV-B-induced up-regulation of PDF1·2 genes. The results indicate that the effects of UV-B on the three sets of genes are mediated through three distinct signal transduction pathways which are similar, but not identical, to pathways initiated in response to pathogen infection. In addition, the increased sensitivity of both jar1 and etr1-1 mutants to UV-B radiation, as compared with wild-type plants, indicated that intact JA and ethylene signal pathways are required for defence against UV-B damage.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Many plant species are sensitive to changes in the seasons, especially with regard to their reproductive behaviour. Sexual or vegetative reproductive structures are often only formed at times of the year when days are sufficiently long, or short. Plants perceive daylength in the leaves, but reproductive changes occur in shoot apices in response to the movement of signals throughout the plant. There is good evidence that phytochrome A is an essential component of the daylength-sensing mechanism in long-day plants, and preliminary evidence suggests a potential interaction between phytochrome C and daylength sensitivity in short-day plants. The sensitivity of reproductive processes to photoperiodic control is directly altered by photoreceptor action, particularly in the case of phytochrome B, which has a major influence on whether flowering or tuberization occurs under non-inductive conditions in both long- and short-day plants, but is not involved in daylength measurement. The signals which move from leaves to the sites of reproductive development are not known, but there is good evidence that gibberellins may be important and some preliminary indication that brassinosteroids might also be involved in photoperiodic signalling.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Experiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far-red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night-break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night-break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo-period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is described.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Supplementary UV-B was shown to lead to a decrease in transcripts encoding the photosynthetic genes Lhcb and psbA and a concomitant increase in transcripts encoding three acid-type pathogenesis-related proteins, PR-1, PR-2 and PR-5, in Arabidopsis thaliana. UV-B radiation has been reported to lead to the generation of reactive oxygen species (ROS). Here we report that ROS are required for UV-B-induced down-regulation of the photosynthetic genes and up-regulation of PR genes, as the addition of antioxidants before UV-B treatment resulted in a marked reduction in the effect of UV-B on both sets of genes. Rises in ROS are frequently accompanied by increases in salicylic acid (SA) accumulation. UV-B treatment of transgenic NahG Arabidopsis plants, which are unable to accumulate SA, showed that the increase in PR transcripts, but not the decrease in photosynthetic transcripts, was dependent on the increase in SA. In addition, a 3 d exposure to UV-B radiation resulted in a 7-fold increase in SA levels. Oxidant treatment of NahG plants indicated that ROS could not up-regulate PR genes in the absence of SA accumulation; however, the down-regulation of photosynthetic transcripts was unchanged from that in wild-type plants. The results indicate that the effects of UV-B on the two sets of genes are mediated through two distinct signal tranduction pathways. One pathway is ROS-dependent but SA-independent and mediates the down-regulation of photosynthetic genes. The other is SA- and ROS-dependent and mediates the up-regulation of the acidic-type PR genes.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The relationship between UV-B-induced changes in gene expression and carbohydrate levels in pea seedlings has been investigated. The effect of supplementary UV-B radiation on the transcript abundance for two photosynthetic genes, photosynthesis, respiration and the levels of carbohydrates was determined in fully expanded leaves of 17-d-old pea seedlings under high (HL: 350 μmol m−2 s−1) and low (LL: 150 μmol m−2 s1) light. Supplementary UV-B caused down regulation of the photosynthetic genes in green leaves under LL and to a lesser extent under HL. In contrast to previous studies, UV-B radiation resulted in a decrease in glucose levels rather than an increase under LL. Sucrose and starch levels were not affected until longer exposure. Effects of UV-B on carbohydrate levels were, however, minimal under HL. The effects on transcript levels were most marked under LL and therefore could not be attributed to elevated carbohydrate levels. Comparison of UV-B effects on carbohydrates in source (leaf) and sink (green buds) organs indicated that changes in carbohydrates in response to UV-B are probably indirect and arise from effects of UV-B on photosynthesis in source organs.
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  • 7
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Two percent of the residents of Bengkala, Bali, have profound, congenital, neurosensory, nonsyndromal deafness due to an autosomal recessive mutation at the DFNB3 locus. We have employed a direct genorne–wide disequilibrium search strategy, allele–frequency–dependent homozygosity ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature genetics 21 (1999), S. 347-349 
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Sound is a well-understood, physical phenomenon. How we perceive sound and make sense of complex auditory stimuli is a different matter altogether. Genetic approaches, however, have provided a powerful strategy to dissect auditory function and to some extent, overcome the challenge posed by the ...
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  • 9
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Neural tissue transplantation has become an alternative treatment for Parkinson's disease (PD)1,2 and other neurodegenerative disorders. The clinical use of neural grafts as a source of dopamine for Parkinson's disease patients, although beneficial, is associated with logistical and ethical issues. ...
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  • 10
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Genomic mismatch scanning (GMS) is a technique that enriches for regions of identity by descent (IBD) between two individuals without the need for genotyping or sequencing. Regions of IBD selected by GMS are mapped by hybridization to a microarray containing ordered clones of genomic DNA from ...
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