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  • 1
    ISSN: 1432-1939
    Keywords: Lycopersicon esculentum ; Biomass partitioning ; Plant stress responses ; Hormonal regulation ; Plant hormone mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract It has been suggested that abscisic acid (ABA) regulates a centralized response of plants to low soil resource availability that is characterized by decreased shoot growth relative to root growth, decreased photosynthesis and stomatal conductance, and decreased plant growth rate. The hypothesis was tested that an ABA-deficient mutant of tomato (flacca; flc) would not exhibit the same pattern of down-regulation of photosynthesis, conductance, leaf area and growth, as well as increased root/shoot partitioning, as its near isogenic wild-type in response to nitrogen or water deficiency, or at least not exhibit these responses to the same degree. Plants were grown from seed in acid-washed sand and exposed to control, nutrient stress, or water stress treatments. Additionally, exogenous ABA was sprayed onto the leaves of a separate group of flc individuals in each treatment. Growth analysis, based on data from frequent harvests of a few individuals, was used to assess the growth and partitioning responses of plants, and gas exchange characteristics were measured on plants throughout the experiment to examine the response of photosynthesis and stomatal conductance. Differences in growth, partitioning and gas exchange variables were found between flc and wild-type individuals, and both nutrient and water treatments caused significant reductions in relative growth rate (RGR) and changes in biomass partitioning. Only the nutrient treatment caused significant reductions in photosynthetic rates. However, flc and wild-type plants responded identically to nutrient and water stress for all but one of the variables measured. The exception was that flc showed a greater decrease in the relative change in leaf area per unit increase of plant biomass (an estimate of the dynamics of leaf area ratio) in response to nutrient stress—a result that is opposite to that predicted by the centralized stress response model. Furthermore, addition of exogenous ABA to flc did not significantly alter any of the responses to nutrient and water stress that we examined. Although it was clear that ABA regulated short-term stomatal responses, we found no evidence to support a pivotal role for ABA, at least absolute amounts of ABA, in regulating a centralized whole-plant response to low soil resource availability.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: SUMMARY1. The plasma calcium and magnesium concentrations of sheep have been manipulated by feeding liquid diets with various calcium and magnesium concentrations.2. When the magnesium status of the diet was low, both plasma calcium and magnesium concentrations declined, but the decline in calcium was much more rapid and extensive when the content of calcium in the diet was also low. This loss of calcium control in magnesium deficiency was attributed to end-organ resistance to parathyroid hormone.3. Correlation between plasma and CSF calcium and magnesium concentrations indicated that convulsions occurred when CSF magnesium and plasma calcium concentrations declined.4. The neurological mechanisms likely to be responsible for the induction of these convulsions are discussed and the factors precipitating convulsions in magnesium deficiency and epilepsy are compared.
    Type of Medium: Electronic Resource
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