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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 4 (1981), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. It is widely believed that the root cap participates in geotropism by acting both as a sensor of the direction of gravity and as a source of at least one regulator of root growth, which may be abscisic acid (ABA). It has been suggested that this regulator accumulates within the prospective concave (or lower) half of the root and there causes a retardation of growth that brings about bending. A re-examination of the evidence upon which this inhibitor hypothesis of geotropic control is based reveals that (1) it is derived almost entirely from microsurgical studies and the deductions from such experiments still require corro-orations from analyses of inhibitor content and action; (2) the evidence that ABA is the inhibitor seems poor at present; (3) in maize and lentil, two well-studied species, geocurvature is probably a consequence of accelerated growth within the prospective convex (or upper) half rather than inhibited growth within the concave (or lower) half; (4) the geotropic signal from the cap may be one that redirects a pre-existing basipetal flow of inhibitor away from the upper
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 96 (1996), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Dark-grown shoots of tubers of the aquatic monocot Potamogön pectinatus L. elongated more strongly in anaerobic than aerobic solutions over 5 days. The response was located in the stem rather than the leaf. Anaerobic carbon dioxide (CO2) production was similar to that in aerobic conditions. Approximately half the anaerobic stem extension was attributed to acidification of the submerging medium by respiratory CO2. Sparging with an anaerobic gas mixture of nitrogen and hydrogen to remove dissolved CO2 inhibited stem elongation and prevented acidification of the medium. Similarly, supplying CO2 anaerobically promoted stem elongation while acidifying the medium. Carbon dioxide was also active on aerobic shoots. The effect of CO2 on anaerobic stem extension could be mimicked with an acidic buffer. Anaerobic stem extension was inhibited by exogenous abscisic acid (ABA), while gibberellic acid and the gibberellin-biosynthesis inhibitor paclobutrazol proved inactive. Exogenous indole-3-acetic acid promoted stem extension in the absence of oxygen. A strong gravitropic response by anaerobic stems of P. pectinatus was inhibited by the auxin-efflux inhibitor naphthylphthalamic acid.
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  • 3
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Soil flooding reduced stomatal conductance (gs) and slowed transpiration, CO2 uptake and leaf elongation in Ricinus communis within 2–6 h. These flood-induced responses developed further over the next 21 h. They were not associated with increased delivery of abscisic acid (ABA) in xylem sap. Instead, ABA delivery from flooded roots decreased 6-fold within 3 h, and remained low thereafter. Root hydraulic conductance (Lp) was depressed 47% below control values within 2 h of soil flooding, and declined further during the next 21 h. The smaller Lp temporarily decreased leaf water potentials (ΨL) by up to −0.4 MPa, and caused visible wilting 3 h into the flooding treatment at 80% relative humidity. Consequently, ABA concentrations in the shoot were increased, as indicated by analyses of phloem sap. Wilting, fall in ΨL and a reduction in gs were delayed for 6 h when 0.6 MPa pneumatic pressure (technical maximum) was applied to the roots. In flooded plants, phloem sap ABA concentrations returned to normal after 24 h. The initial stomatal closure, caused by soil flooding in R. communis, is attributed to decreased leaf hydration arising from the reduced LP of oxygen-deficient roots. Continued stomatal closure and slow leaf expansion beyond 24 h were presumably achieved by non-hydraulic means.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 46 (1979), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The production of ethylene by a mutant form of tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) with diageotropic shoot growth was compared with that from non-mutant, upright plants. No difference in the rate of production by segments of petiole or stem apex was observed. The amounts of ethylene produced by excised segments of petiole from diageotropic and upright plants in response to wounding were also comparable.When the roots of either kind of plant were exposed to anaerobic conditions, the production of ethylene increased in the petioles; in ordinary plants this was associated with epinastic curvature, while in diageotropic plants the direction of shoot extension became reorientated from the horizontal to a more upright position. Exogenous ethylene gas had similar effects.These results support the view that the mutant has a modified response mechanism to gravity and to ethylene rather than an abnormally slow rate of ethylene production in the shoot. Since applying inhibitors of ethylene action to non-mutant, upright plants did not induce diageotropism, endogenous ethylene seems unlikely to play a significant role in maintaining their upright orientation.The roots of both kinds of plant produced large amounts of ethylene, although the rate for diageotropic roots was about 37% less than that of roots from normal plants. Application of indol-3-ylacetic acid increased the production of ethylene by all roots but those from mutant plants were less responsive.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 52 (1981), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Previous studies have shown increases in the concentration of ethylene in the soil and roots of plants when the soil is water saturated (flooded). In Zea mays L. this occurs in association with an overall reduction in growth but without extensive foliar senescence and in conjunction with the development of an adventitious root system. We have assessed the possibility that ethylene may be involved in these responses to flooding. Mixtures of the gas in air were therefore supplied to the roots and stem-base of Z. mays growing in nutrient solution.Seven or 14 d exposure to ethylene (1 or 5 νl 1−1) inhibited seminal root elongation and growth in dry weight and accelerated the emergence of adventitious roots, although their final length and dry weight were depressed. Leaf extension was inhibited by 0.1,1.0 or 5.0 μl 1−1 ethylene around the roots; leaves extending rapidiy at the start of treatment were the most sensitive. Final shoot fresh and dry weights were depressed by the gas but tie shootrroot dry weighl ratio and percentage dry matter were not affected greatly. Leaf chlorosis was not observed but the concentration of phosphorus in the shoots was 26 to 31% below normal.When aeration of the nutrient solution was stopped, the concentration of dissolved oxygen declined and the concentration of ethylene in the roots increased. Similar changes occur in response to soil flooding. Root and shoot growth was slowed by non-aeration although the shootroot dry weight ratio remained unchanged. The phosphorus concentration of the shoots was depressed but there was little chlorosis or leaf death. The similarity in these respects between the effects of ethylene and non-aeration suggests that in flooded Z. mays, ethylene contributes to their development by accelerating the emergence of adventitioos roots, inhibiting phosphorus accumulation in the shoots and by a non-toxic inhibition of plant growth.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. We have examined the widely held theory that ethanol toxicity is a prime cause of the injury and death of plants in soil flooded with water. The tests were made on peas (Pisum sativum L.) at the early flowering or fruiting stages, when they are known to be severely injured by flooding.Supplying ethanol in aerobic or anaerobic nutrient solution at similar concentrations to those we found in flooded soil (up to 3.9 mol m−3) or in the xylem sap of flooded pea plants (up to 2.1 mol m−3) caused no injury. One hundred times these concentrations gave little extra effect and failed to simulate flooding injury. Isolated leaf protoplasts and detached leaves were also resistant to damage by ethanol at these concentrations.Other published measurements of ethanol concentrations in flooded plants are similar to or less than those we report for pea plants. Exceptions include root nodules and germinating pea seeds. Reports by others of responses to applied ethanol in a wide variety of circumstances confirm that in flooded plants the amounts are probably too small to explain the observed injury. Alternative mechanisms are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 225 (1970), S. 1019-1022 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Natural leaf fall is triggered by increased ethylene production in senescing cells close to abscission ...
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  • 8
    ISSN: 1432-2048
    Keywords: Aerenchyma ; Ethylene ; Gas space ; Oxygen and gas-space formation ; Roots, adventitious ; Silver ions ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have studied the role of ethylene in accelerating the lytic formation of gas spaces (aerenchyma) in the cortex of adventitious roots of maize (Zea mays L.) growing in poorly aerated conditions. Such roots had previously been shown to contain increased concentrations of ethylene. Ten day-old maize plants bearing seminal roots and one whorl of emerging adventitious roots were grown in nutrient solution bubbled with air, ethylene in air (0.1 to 5.0 μl l−1), or allowed to become oxygen-deficient in nonaerated (but not completely anaerobic) solution. Additions of 0.1 μl l−1 ethylene or more promoted the formation of aerenchyma, with lysis of up to 47% of the cortical cells. The effects of non-aeration were similar to those of exogenous ethylene. When silver ions, an ethylene antagonist, were present at low, non-toxic concentrations (circa 0.6 μM), aerenchyma formation was prevented in ethylene treated roots and in those exposed to oxygen deficiency. Silver ions also blocked the inhibiting effect of exogenous ethylene on root extension. By contrast, the suppression of aerenchyma formation by silver ions under oxygendeficient conditions was associated with a retardation of root extension, indicating the importance of aerenchyma for root growth in poorly aerated media. Rates of production of ethylene by excised roots were stimulated by a previous non-aeration treatment. The effectiveness of Ag+ in inhibiting equally the action on cortical cells of exogenous ethylene and of non-aeration, supports the view that gas space (aerenchyma) formation in adventitious roots ‘adpted’ to oxygendeficient environments is mediated by increased concentrations of endogenous ethylene. The possibility that extra ethylene could arise from increased biosynthesis of a precursor in root tissues with a restricted oxygen supply is discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Planta 129 (1976), S. 273-274 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A delay of 20 to 30 min precedes a rapid increase in the production of ethylene when segments are excised from the petioles of tomato plants. Measurements made during this early phase may be better estimates of production by petioles on the intact plant than those made at later times.
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  • 10
    ISSN: 1573-5087
    Keywords: gas chromatography ; nitrogen/phosphorus detector ; 1-aminocyclopropane-1-carboxylic acid (ACC) ; soil flooding ; root-shoot communication ; xylem sap ; environmental stress ; Lycopersicon esculentum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The Lizada and Yang method, commonly used for analyzing 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of the plant hormone ethylene, is subject to interference and lacks internal standards. The use of combined gas chromatography-mass spectrometry (GC-MS) overcomes these shortcomings but the method is expensive and unavailable to many laboratories. We describe an alternative physico-chemical method using a capillary column gas chromatograph fitted with a standard nitrogen/phosphorus detector. After forming the N-benzoyl n-propyl derivative, measurements of ACC concentrations in extracts of leaves and in xylem sap of tomato plants using the nitrogen/phosphorus detector were within 10% of those obtained by GC-MS. Concentrations in plants grown in well-drained soil were approximately 0.16 nmol g−1 fresh weight (leaves) and 0.04–0.01 mmol m−3 (sap). Flooding the soil for 48–72 h increased these values approximately 9-fold.
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