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  • Gravitropism (root)  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Cellular specificity of the gravitropic motor response in roots (1997)
    Springer
    Planta 203 (1997), S. S115 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis ; Auxin ; Calcium ; Distal elongation zone ; Gravitropism (root) ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. A number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ), a group of cells located between the meristem and the main elongation, not within the central elongation zone; and (iii) the initiation of differential growth in the DEZ appears to be independent of the establishment of auxin asymmetry. Alternative candidates for mediation of differential growth in the DEZ include calcium ions and protons. Gravi-induced curvature is accompanied by polar movement of calcium toward the lower side of the maize root tip and the DEZ is shown to be particularly sensitive to growth inhibition by calcium. Also, gravistimulation of maize roots causes enhanced acid efflux from the upper side of the DEZ. Evidence for gravi-induced modification of ion movements in the root tip includes changes in intracellular potentials and current flow. It is clear that there is more than one motor region in the root with regard to gravitropic responses and there is evidence that the DEZ itself consists of more than one class of responding cells. In order to gain a more complete understanding of the mechanism of gravitropic curvature, the physiological properties of the sub-zones of the root apex need to be thoroughly characterized with regard to their sensitivity to hormones, calcium, acid pH and electrical perturbations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008099
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  • 2
    Electronic Resource
    Electronic Resource
    The kinetics of abscisic acid action on root growth and gravitropism (1983)
    Springer
    Planta 157 (1983), S. 150-157 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid and root growth ; Acid efflux and root growth ; Aminoethoxyvinylglycine ; Gravitropism (root) ; Phaseic acid ; Pisum (root growth) ; Root growth (hormones) ; Zea (root growth)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using an auxanometer and time-lapse cinematography we have studied the timing of abscisic acid (ABA) effects on elongation, gravitropic curvature, and hydrogen-ion efflux in several cultivars of maize (Zea mays L.). The effect of high concentrations (e.g. 0.1 mM) of ABA on root elongation is triphasic, including 1) a period of promotion lasting approximately 12 h, 2) a subsequent period of increasing inhibition lasting approximately 12h, and 3) gradual recovery to a rate within approximately 80% of the control rate. With lower concentrations of ABA (e.g. 0.1 μM) only the transient promotive phase is seen. Abscisic acid enhances ethylene biosynthesis in roots of maize but suppression of ethylene biosynthesis does not prevent the long-term inhibitory action of ABA on growth. Application of ABA (0.1 mM) to the upper surface of horizontally placed roots accelerates positive gravitropism. Application of ABA to the lower surface retards gravitropism and in some cases causes the roots to curve upward against the direction of gravity. These observations are consistent with our finding that the initial effect of ABA on root elongation is stimulatory. Since root gravitropism is rapid enough to be completed within the stimulatory phase of ABA action, the data argue against hypotheses of gravitropism based upon accumulation of ABA to inhibitory levels on the lower side of a hirizontal root.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393649
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    Paper (German National Licenses)
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