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  • Avena  (3)
  • Coleoptile  (3)
  • Springer  (6)
  • 1990-1994  (2)
  • 1980-1984  (4)
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  • Springer  (6)
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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of phytochrome kinetics in light-grown Avena sativa L. seedlings (1983)
    Springer
    Planta 157 (1983), S. 392-400 
    Details
    ISSN: 1432-2048
    Keywords: Avena ; Phytochrome destruction ; Phytochrome synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phytochrome content, the rate of phytochrome accumulation after a light/dark transition and the rate of phytochrome destruction after a 1.5 d reaccumulation period in darkness were measured in light grown Avena sativa L. seedlings. The results using spectrophotometrical methods (Norflurazon treated seedlings) and the radio-immunoassay (RIA) (green seedlings) were almost identical. The rate of phytochrome synthesis was analysed by measuring the activity of poly(A+)-RNA coding for the phytochrome apoprotein. It was demonstrated that the rate of phytochrome synthesis is different in light and in dark. These results were confirmed by measuring the incorporation of radioactive label in vivo. Five minutes red (and 5 min far-red) light strongly reduces the rate of phytochrome synthesis. Even after prolonged dark periods only 50% of the initial rate of phytochrome synthesis is recovered for light and dark grown seedlings which received one red light pulse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397196
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Phytochrome-controlled extension growth of Avena sativa L. seedlings (1982)
    Springer
    Planta 154 (1982), S. 224-230 
    Details
    ISSN: 1432-2048
    Keywords: Avena ; Coleoptile growth ; Mesocotyl growth ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of Pfr, the far-red light absorbing form of phytochrome (e.g., by [Pfr]≈0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by Pfr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to Pfr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by Pfr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of Pfr established at the onset of darkness rather than by the actual Pfr level present during the growth period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387868
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  • 6
    Electronic Resource
    Electronic Resource
    Phytochrome-controlled extension growth of Avena sativa L. seedlings (1982)
    Springer
    Planta 154 (1982), S. 231-240 
    Details
    ISSN: 1432-2048
    Keywords: Avena ; Phytochrome ; Coleoptile growth ; High irradiance reaction ; Light and growth ; Mesocotyl growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fluence rate response curves for light-induced inhibition of mesocotyl growth and promotion of coleoptile growth in etiolated Avena sativa L. (cv. Victory) were developed. The irradiation time was 24 h. Fluence rates between 10-6 and 105 nmol m-2s-1 and 30 wavelengths between 563 and 1,093 nm were used. The main conclusions are as follows: 1. Both organs exhibit a low fluence rate response as well as a high fluence rate response. 2. The mesocotyl response is more sensitive to light than the coleoptile response. 3. The low fluence rate response of the mesocotyl shows a threshold of sensitivity at about 10-7 nmol m-2s-1 (i.e., total fluence of 5·10-2 nmol m-2 during the experiment) in the red and a saturation (about 70% inhibition of growth) at 10-4 nmol m-2s-1 (50 nmol m-2). 4. The action spectrum for the low fluence rate response parallels the Pr absorption spectrum. Alterations induced by screening are discussed. 5. The action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (Pr→Pfr) up to about 800 nm. Between 800 and 1,093 nm the photoconversion cross-section is only weakly dependent on wavelength. 6. The action spectrum for the high fluence rate response shows a broad peak in the red, a trough at 723 nm, and a sharp peak at 740–750 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387869
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