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  • Abscisic acid and photosynthesis  (1)
  • Osmotic potential  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Auxin action on growth in intact plants: Threshold turgor is regulated (1994)
    Springer
    Planta 193 (1994), S. 44-50 
    Details
    ISSN: 1432-2048
    Keywords: Glycine ; Growth ; Osmotic potential ; Threshold turgor ; Turgor ; Water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The guillotine thermocouple psychrometer allows auxin action on cell enlargement to be investigated in intact plants. Because the technique measures all the physical parameters affecting enlargement in the same plants, close comparisons can be made of the changes brought about by this growth regulator. In etiolated seedlings of soybean (Glycine max L. Merr.), auxin was supplied endogenously by the intact plant or was depleted by removing the apical portion of the stem. We observed that, when stem growth was rapid in the intact plant, the water potential of the growing region was lower than in the nongrowing region but, as growth slowed during auxin depletion, the water potential rose until it became essentially the same as in the nongrowing region. This indicated that gradients in water potential had been induced by the demand for water during rapid growth but had decreased as growth decreased in the auxin-depleted cells. The turgor appeared to rise slightly as growth slowed which is in the wrong direction to account for the growth change unless compensating changes occurred in wall properties and/or synthesis. As growth ceased in the auxin-depleted tissue, the threshold turgor rose until it became nearly the same as the cell turgor, which indicates that auxin affected this wall parameter. The osmotic potential increased slightly, probably because of a dilution of the cell contents by the residual growth occurring after the stem apex (and cotyledons) had been removed. The hydraulic conductance for water was unaffected by auxin status whether it was measured in the whole enlarging region or in individual cortical cells from the region. It was concluded that auxin acts mainly on the metabolism of the cell walls manifested by the change in growth rate and threshold turgor. The other changes were passive responses to the changed growth rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191605
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  • 2
    Electronic Resource
    Electronic Resource
    Very high CO2 partially restores photosynthesis in sunflower at low water potentials (1990)
    Springer
    Planta 181 (1990), S. 378-384 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid and photosynthesis ; Carbon dioxide pressures and photosynthesis ; Gas exchange ; Helianthus ; Photosynthesis and dehydration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We re-examined the question of whether the stomata limit photosynthesis in dehydrated sunflower (Helianthus annuus L.) plants having low leaf water potentials. A gas-exchange apparatus was modified to operate at external CO2 partial pressures as high as 3000 Pa (3%), which were much higher than previously achieved. This allowed photosynthesis and stomatal behavior to be monitored simultaneously at very high CO2 in the same leaf. The data were compared with those from leaves treated with abscisic acid (ABA) where effects on photosynthesis are entirely stomatal. Photosynthesis was inhibited at low water potential and was only slightly enhanced by increasing the external CO2 partial pressure from 34 Pa (normal air) to 300 Pa. Photosynthesis in ABA-treated leaves was similarly inhibited but recovered fully at 300 Pa. In both cases, the stomata closed to the same extent as judged from the average conductance of the leaves. Because the ABA effect resulted from diffusion limitation for CO2 caused by stomatal closure, the contrasting data show that most of the dehydration effect was nonstomatal at low water potentials. When CO2 partial pressures were raised further to 3000 Pa, photosynthesis increased somewhat at low water potentials but not in ABA-treated leaves. This indicates that some nonstomatal component of photosynthesis responded differently in leaves at low water potential and leaves treated with ABA. Because this component was only partially restored by very high CO2, it was likely to be metabolic and was an important source of photosynthetic inhibition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195891
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