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  • Coleoptile  (6)
  • Springer  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Interaction of gravi- and phototropic stimulation in the response of maize (Zea mays L.) coleoptiles (1988)
    Springer
    Planta 173 (1988), S. 213-220 
    Details
    ISSN: 1432-2048
    Keywords: Coleoptile ; Gravitropism ; Phototropism ; Zea (gravitropism, phototropism)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of gravitropic stimulation upon blue-light-induced first positive phototropism for stimulations in the same (light source and center of gravity opposite to each other) and in opposing directions was investigated in maize cole-optiles by measuring fluence-response patterns. As a result of gravitropic counterstimulation, phototropic bending was transient with maximum curvature occurring 100 min after stimulation. On a horizontal clinostat, however, the seedlings curved for 20 h. Gravistimulation in the opposite direction acted additively upon blue-light curvature. Gravistimulation in the same direction as phototropic stimulation produced a complex behaviour deviating from simple additivity. This pattern can be explained by a gravitropically mediated sensitization of the phototropic reaction, an optimal dependence of differential growth on the sum of photo-and gravistimulation, and blue-light-induced inhibition of gravitropic curvature at high fluences. These findings indicate that several steps of photo-and gravitransduction are separate. Preirradiation with red light desensitized the system independently of applied gravity-treatment, indicating that the site of red-light interaction is common to both transduction chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403013
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  • 2
    Electronic Resource
    Electronic Resource
    Spatial memory during the tropism of maize (Zea mays L.) coleoptiles (1988)
    Springer
    Planta 175 (1988), S. 380-388 
    Details
    ISSN: 1432-2048
    Keywords: Coleoptile ; Gravitropism ; Phototropism ; Polarity, transverse ; Spatial memory ; Zea (tropisms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photo- or gravitropic stimulation of graminean coleoptiles involves the formation of putative tropistic transverse polarities. It had been postulated that these polarities can be extended by stabilization to developmentally active polarities. Such polarities are known from unicellular spores and zygotes of lower plants and regeneration experiments in dicotyledonous plants. In coleoptiles, photo- or gravitropic stimulation results in stability to counterstimulation of equal strength (with only transient bending in the direction of the second stimulus), as a result of a directional memory, if the time interval between both stimuli exceeds 90 min. This directional memory develops from a labile precursor, which is present from at least 20 min after induction. Once it is stable, spatial memory is conserved for many hours. The formation of spatial memory involves at least one step not present in the common tropistic transduction chain. The spatial expression of memory as curvature is restricted to three distinct responses: (i) curving in the direction of the first stimulus (for time intervals exceeding 90 min); (ii) curving in the direction of the second stimulus (for time intervals shorter than 65 min); and (iii) zero-curvature (for time intervals between 65 and 90 min). This can be interpreted in terms of a stable transverse polarity, which is not identical with the putative tropistic transverse polarity, but might be an extension of it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396344
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  • 3
    Electronic Resource
    Electronic Resource
    Phototropism of maize coleoptiles Influences of light gradients (1988)
    Springer
    Planta 176 (1988), S. 212-220 
    Details
    ISSN: 1432-2048
    Keywords: Blue-light receptor ; Coleoptile ; Phytochrome (light gradient) ; Phototropism (bluelight receptor) ; Zea (phototropism)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The lateral fluence-rate gradients in unilaterally irradiated maize (Zea mays L.) coleoptiles were calculated on the basis of the proportions of P fr (far-red-absorbing form of phytochrome) measured spectroscopically in transverse slices of the coleoptiles (top 1 cm). The results showed the occurrence of significant gradients that are wavelength-dependent. The gradient at 449 nm was steeper than those measured at 516, 534 and 551 nm, which were steeper than that measured at 665 nm. The ratios between the sides proximal and distal to the light source were, for example, 1:0.12 (449 nm), 1:0.23 (534 nm), and 1:0.28 (665 nm). Fluence-response curves for coleoptile phototropism (first positive curvature produced by less than 100 s unilateral irradiation) were measured at 449, 516, 534 and 551 nm. Comparison of the threshold fluences indicated that the responsiveness to 551 nm is about 104.8 less than that to 449 nm. Increasing wavelengths led to a decrease in maximal curvature, which correlated with the decrease of the fluence-rate ratios between the proximal and distal sides. Phototropic fluence-response curves were also measured using bilateral irradiation (449 nm). In one set of experiments, the fluence ratio was kept constant (either 1:1/2, 1:1/4 or 1:1/16) and the total fluence was varied, and in the other set the fluence applied to one side was kept constant and the fluence ratio was varied. A simple model based on the assumption that only one photoreaction occurs, and that the response is a function of the difference between the proximal and distal sides in the local photoreceptor action was tested. A fluence-response curve for this local photoreceptor action was calculated based on the fluence-rate ratio and the phototropic fluence-response curve measured for 449 nm. This curve was used, in conjunction with the measured fluence-rate ratios, as a basis for calculating phototropic fluence-response curves for other wavelengths and those for 449 nm obtained with bilateral irradiation. The calculated fluence-response curves showed excellent agreement with the experimental data. It is concluded that the threshold for maize coleoptile phototropism reflects the apparent photoconversion cross-section of the blue-light receptor whereas the maximal curvature depends on the steepness of the light gradient across the coleoptile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392447
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  • 4
    Electronic Resource
    Electronic Resource
    Polarity induction versus phototropism in maize: Auxin cannot replace blue light (1994)
    Springer
    Planta 195 (1994), S. 63-69 
    Details
    ISSN: 1432-2048
    Keywords: Auxin ; Blue light ; Coleoptile ; Microtubule ; Phototropism ; Transverse polarity ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a previous study (Nick and Schäfer 1991, Planta 185, 415–424), unilateral blue light had been shown, in maize coleoptiles, to induce phototropism and a stable transverse polarity, which became detectable as stable curvature if counteracting gravitropic stimulation was removed by rotation on a horizontal clinostat. This response was accompanied by a reorientation of cortical microtubules in the outer epidermis (Nick et al. 1990, Planta 181, 162–168). In the present study, this stable transverse polarity is shown to be correlated with stability of microtubule orientation against blue light and changes of auxin content. The role of auxin in this stabilisation was assessed. Although auxin can induce reorientation of microtubules it fails to induce the stabilisation of microtubule orientation induced by blue light. This was even true for gradients of auxin able to induce a bending response similar to that ellicited by phototropic stimulation. Experiments involving partial irradiation demonstrated different perception sites for phototropism and polarity induction. Phototropism starts from the very coleoptile tip and involves transmission of a signal (auxin) towards the subapical elongation zone. In contrast, polarity induction requires local action of blue light in the elongation zone itself. This blue-light response is independent of auxin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206293
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  • 5
    Electronic Resource
    Electronic Resource
    Induction of transverse polarity by blue light: An all-or-none response (1991)
    Springer
    Planta 185 (1991), S. 415-424 
    Details
    ISSN: 1432-2048
    Keywords: Blue light (polarity induction) ; Coleoptile ; Phototropism ; Polarity (transverse) ; Signal transduction ; Zea (phototropism)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phototropic stimulation induces a spatial memory. This was inferred from experiments with maize (Zea mays L.) coleoptiles involving opposing blue-light pulses, separated by variable time intervals, and rotation on a horizontal clinostat (Nick and Schäfer, 1988b, Planta 175, 380–388). In those experiments, individual seedlings either curved towards the first or towards the second pulse, or they remained straight. Bending, if it occurred, seemed to be an all-or-none response. Intermediates, i.e. plants, bending only weakly, were not observed. In the first part of the present study it was attempted to create such intermediates. For this purpose the strength of the first, inducing, and the second, opposing, pulse was varied. The result was complex: (i) Individual seedlings maintained the all-or-none expression of spatial memory. (ii) However, on the level of the whole population, the time intervals at which a given response type dominated depended on the fluence ratio. (iii) Furthermore, the final curvature was determined by the fluence ratio. These results are discussed in terms of a blue-light-induced transverse polarity. This polarity initiates from a labile precursor, which can be reoriented by an opposing stimulation (indicated by the strong bending towards the second pulse). The strong curvatures towards the first pulse over long time intervals reveal that, eventually, the blue-light-induced transverse polarity becomes stabilised and thus immune to the counterpulse. In the second part of the study, the relation between phototropic transduction and transverse polarity was characterised by a phenomenological approach involving the following points: (i) Sensory adaptation for induction of transverse polarity disappears with a time course similar to that for phototropic sensory adaptataion. (ii) The fluence-response for induction of transverse polarity is a saturation curve and not bell-shaped like the curve for phototropism. (iii) For strong counterpulses and long time intervals the clinostat-elicited nastic response (Nick and Schäfer 1989, Planta 179, 123–131) becomes manifest and causes an “aiming error” towards the caryopsis. (iv) Temperature-sensitivity of polarity induction was high in the first 20 min after induction, then dropped sharply and rose again with the approach of polarity fixation. (v) Stimulus-summation experiments indicated that, for different inducing fluences, the actual fixation of polarity happened at about 2 h after induction. These experiments point towards an early separation of the transduction chains mediating phototropism and transverse polarity, possibly before phototropic asymmetry is formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201066
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  • 6
    Electronic Resource
    Electronic Resource
    Phytochrome-mediated phototropism in maize seedling shoots (1984)
    Springer
    Planta 160 (1984), S. 41-51 
    Details
    ISSN: 1432-2048
    Keywords: Coleoptile ; Mesocotyl ; Phototropism (red and blue light) ; Phytochrome and phototropism ; Zea (phototropism)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Unilateral irradiation with red light (R) or blue light (BL) elicits positive curvature of the mesocotyl of maize (Zea mays L.) seedlings raised under R for 2 d from sowing and kept in the dark for 1 d prior to curvature induction. The fluenceresponse curve for R-induced mesocotyl curvature, obtained by measuring curvature 100 min after phototropic induction, shows peaks in two fluence ranges, designated first positive range (from the threshold to the trough), and second positive range (above the trough). The fluence-response curve for BL is similar to that for R but shifted two orders of magnitude to higher fluences. Blue light elicits the classical first positive curvature of the coleoptile, whereas this response is not found with R. Positive mesocotyl curvature induced by either R or BL is eliminated by R given from above just before the unilateral irradiation, whereas BL-induced coleoptile curvature is not eliminated. The above results collectively offer evidence that phototropic curvature of the mesocotyl is induced by R-sensitive photosystem(s). Mesocotyl curvature in the second positive range is reduced by vertical far-red light (FR) applied after phototropic induction with R, but is not affected by FR applied before R. Unilateral irradiation with FR following vertical irradiation with a high R fluence leads to negative curvature of the mesocotyl. It is concluded that mesocotyl curvature in the second positive range results from a gradient in the amount of the FR-absorbing form of phytochrome (Pfr) established across the plant axis. Mesocotyl curvature in the first positive range is inhibited by vertical FR given either before or after phototropic induction with R. Since the FR used here is likely to produce more Pfr than the very low fluences of R eliciting the mesocotyl curvature in the first positive range, it is assumed that FR reduces the response in this case by adding Pfr at both sides of the plant axis. By rotating seedlings on a clinostat with its axis horizontal, the kinetics of mesocotyl curvature can be studied in the absence of a counteracting gravitropic response. On the clinostat, the R-induced mesocotyl curvature develops after a lag, through two successive phases having different curvature rates, the late phase is slower than the early phase. Negative curvature of the coleoptile can be induced by either R or BL; the BL-induced negative curvature is found at fluences higher than those giving positive curvature. The clinostat experiments show that the negative coleoptile curvature induced by either R or BL is a gravitropic compensation for positive mesocotyl curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392464
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