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  • 1
    Electronic Resource
    Electronic Resource
    Uptake and decarboxylation of indole-3-acetic acid during auxin-induced growth in lupin hypocotyl segments (1994)
    Springer
    Planta 193 (1994), S. 224-231 
    Details
    ISSN: 1432-2048
    Keywords: Acid-growth theory ; ATPase ; auxin (uptake, decarboxylation) ; Growth (auxin induced) ; Lupinus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The elongation growth of etiolated hypocotyl segments of lupin (Lupinus albus L.) was stimulated by acid pH (4.6 versus 6.5) and by IAA for periods of up to 4 h. After this time, the segments were unable to grow further. In the presence of an optimal IAA concentration (10 μM), acid pH increased the growth rate but had no effect on final growth. With suboptimal IAA (0.1 μM), however, acid pH increased growth in a more than additive way, suggesting a synergistic action between the two factors. This synergism may be explained by the increased IAA uptake and decarboxylation seen at an acid pH. These results reinforce the view that the effects of low pH and IAA on growth are not independent. Vanadate inhibited growth and also IAA uptake and decarboxylation. This inhibitor, therefore, probably inhibits growth not only by decreasing ATPase-mediated acidification but also by decreasing H+-dependent IAA uptake from the apoplasm. This dependence of IAA uptake on ATPase may be mediated by apoplasmic acidification. The amount of IAA decarboxylated increased when the assay conditions favored the growth of segments, indicating that IAA could be destroyed by decarboxylation during the auxin-induced growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192534
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  • 2
    Electronic Resource
    Electronic Resource
    CO2 Exchange in soil algal crusts occurring in the trachypogon savannas of the Orinoco Llanos, Venezuela (1991)
    Springer
    Plant and soil 135 (1991), S. 233-244 
    Details
    ISSN: 1573-5036
    Keywords: CO2 exchange ; soil algal crust ; Trachypogon savannas ; water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract CO2 exchange between the atmosphere and soil algal crusts of the Trachypogon savannas of the Orinoco Llanos has been analyzed using an open gas exchange system. These savannas encompass a wide range of physiognomic types, from herbaceous communities to savanna woodlands. A maximum CO2 flux of 0.207 mg m-2 s-1 was measured in the crusts of the Guanipa savannas, while in the other examined crusts (0.035–0.105 mg m-2 s-1) the flux was similar to values reported for terrestrial algae. The CO2 flux data were statistically fitted to the photosynthetically active radiation by a logarithmic relationship, and the photosynthetic efficiencies of the crusts were compared. The activation energy calculated for the CO2 fixation indicates that limitations by diffusion and photochemical processes were excluded in the Guanipa crusts (above 12 kcal mole-1), whereas they were evident in the other crust studied. An optimum CO2 incorporation as a function of the crust water potential was established and carbon gain strategies were proposed on the basis of the results and characteristics of the habitats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010911
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    Paper (German National Licenses)
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