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  • 1
    ISSN: 1600-065X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary:  Parasitic protozoa of the genus Leishmania have provided a useful perspective for immunologists in terms of host defense mechanisms critical for the resolution of infection caused by intracellular pathogens. These organisms, which normally reside in a late endosomal, major histocompatibility complex (MHC) class II+ compartment within host macrophages cells, require CD4+ T-cell responses for the control of disease. The paradigm for the CD4+ T-helper 1 (Th1)/Th2 dichotomy is largely based on the curing/non-curing responses, respectively, to Leishmania major infection. However, this genus of parasitic protozoa is evolutionarily diverse, with the cutaneous disease-causing organisms of the Old World (L. major) and New World (Leishmania mexicana/ Leishmania amazonensis) having diverged 40–80 million years ago. Further adaptations to survive within the visceral organs (for Leishmania donovani, Leishmania chagasi, and Leishmania infantum) must have been required. Consequently, significant differences in host–parasite interactions have evolved. Different virulence factors have been identified for distinct Leishmania species, and there are profound differences in the immune mechanisms that mediate susceptibility/resistance to infection and in the pathology associated with disease. These variations not only point to interesting features of the host–pathogen interaction and immunobiology of this genus of parasitic protozoa, but also have important implications for immunotherapy and vaccine development.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants respond to Cd by synthesising phytochelatins (PC) and similar S-rich peptides which are important in alleviating Cd toxicity. The hypothesis that S nutrition influences the sensitivity of plants to Cd was examined by measuring the growth, PC and Cd content of wheat plants (Triticum aestivum cv. Condor) grown at 10–1000 µM S with and without 30 µM Cd. In the absence of Cd, 100 µM S was marginally S-limiting. Cd severely inhibited root growth at 100 µM S but the concentrations of PC, Cd–PC complexes and Cd in the root were similar to those of plants grown at 1000 µM S which exhibited no evidence of Cd toxicity. Plants grown at low S (10 and 30 µM) contained lower concentrations of Cd. However, they produced very low amounts of PC and were very sensitive to Cd. At 10–300 µM S (but not at 1000 µM), Cd enhanced the concentration of S in the root. The data are consistent with a model in which plants preferentially allocate S to PC synthesis. When S was marginally limiting (100 µM), the S supply was sufficient for PC synthesis but not root growth, effectively causing Cd-induced S deficiency. This did not occur at high S (1000 µM). Conversely, at low S (10 and 30 µM), the synthesis of PC2–PC4 was decreased by 87 and 66%, respectively, thereby resulting in decreased Cd uptake while also making the plants especially sensitive to Cd.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 109 (2000), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Although cyanide has long been recognized as a co-product of ethylene synthesis, little attention has been given to its potential physiological and molecular roles. In the present work, the long-term effects of cyanide on growth and development were observed in Arabidopsis thaliana. Two days after a single 20-min application of cyanide, plants demonstrated visible signs of stress. Long-term detrimental effects on growth and photosynthetic capabilities were noted, including low chlorophyll accumulation and stunted growth. Because of the relationship between cyanide and ethylene production, we chose to evaluate the results of cyanide treatment on genes encoding proteins involved in ethylene synthesis. We have found that only the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene, ACS6, is rapidly activated in response to cyanide treatment, while other ACS genes were unaffected. This same gene has previously been shown to be transcriptionally activated in response to touch and other environmental stimuli. Cyanide was capable of activating ACS6 transcription within 10 min of treatment, and the amount of transcript correlated positively with the cyanide dosage. Due to the toxic nature of cyanide, plant in vivo concentrations are generally maintained lower than 10 μM, but can increase under certain stresses. In the present work, we observed that physiologically relevant concentrations as low as 1 μM HCN, considered metabolically ‘safe’, were capable of initiating ACS6 transcription. ACS6 transcripts were not substantially reduced as a result of multiple cyanide treatments, which is in contrast with the effects of mechanical stimulation on transcription. Our results suggest a relationship between cyanide production during ethylene synthesis and the molecular control of ethylene synthesis. This work corresponds with earlier experiments that have demonstrated that ethylene and cyanide can elicit some similar physiological responses. It is possible that cyanide may play an active role in ethylene regulation under conditions where rapid cyanide accumulation occurs. Since cyanide can rapidly activate ethylene synthesis, it is possible that it is involved in the positive-feedback regulation of ethylene that occurs in some plant tissues.
    Type of Medium: Electronic Resource
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