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  • 1
    Electronic Resource
    Electronic Resource
    Light requirement, phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois (1978)
    Springer
    Planta 141 (1978), S. 15-22 
    Details
    ISSN: 1432-2048
    Keywords: Flowering ; Pharbitis ; Photoperiodic induction ; Phytochrome ; Spectrophotometry (phytochrome)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During an inductive dark period for flowering, changes in phytochrome have been followed in cotyledons of Pharbitis nil seedlings using a spectrophotometric and a physiological technique. There was agreement between the two techniques, both indicating a rapid lowering of the levels of the far-red-absorbing form of the pigment (Pfr) during the first 30–90 min of darkness. Thus, Pfr could provide the cue which signals the beginning of darkness and the length of the critical dark period was, in some instances, correlated with the time of Pfr disappearance. However, there was no correlation with another indicator of photoperiodic time measurement, the time in darkness at which a brief night interruption becomes inhibitory to flowering. These results imply that the transition from light to darkness is not signalled by the disappearance of Pfr. However, the involvement of other photoreceptors seems unlikely. Thus, some mode of phytochrome action other than a simple Pfr-mediated response may be involved in the light/dark-sensing reactions of photoperiodism
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387738
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  • 2
    Electronic Resource
    Electronic Resource
    The relative significance for stem elongation and flowering in Lolium temulentum of 3β-hydroxylation of gibberellins (1993)
    Springer
    Planta 192 (1993), S. 130-136 
    Details
    ISSN: 1432-2048
    Keywords: Lolium ; Gibberellin ; Flowering ; Stem elongation ; 3β-Hydroxylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In previous experiments with many gibberellins (GAs) and GA derivatives applied to Lolium temulentum L., quite different structural requirements were evident for stem elongation on the one hand and for the promotion of flowering on the other. Whereas hydroxylation at carbons 12, 13 and 15 enhanced flowering relative to stem growth, the reverse was the case at carbon 3 (L.T. Evans et al. 1990, Planta 182, 97–106). The significance of hydroxylation at carbon 3 is examined in this paper. The application of inhibitors of 3β-hydroxylation, including C/D-ring-rearranged GAs, reduced stem growth but, in the case of the two acylcyclohexanediones, increased the flowering response when applied on the inductive long day. Later applications of the acylcyclohexanediones, made after floral initiation had occurred, were inhibitory to flowering, suggesting that subsequent inflorescence development requires 3β-hydroxylated GAs. Applications of the 3α-hydroxy epimers of GA1, GA3 and GA4 gave slightly less promotion of flowering in comparison with the 3β-hydroxy GAs, but far less promotion of stem elongation, except in the case of 3-epi-GA4, which was comparable to GA4. The 3α-hydroxy epimer of 2,2-dimethyl GA4 gave less promotion of flowering than its 3β-hydroxy epimer but almost no promotion of stem elongation. The 3α-hydroxy epimers of GA3 and 2,2-dimethyl GA4 did not act as competitive inhibitors of the stem elongation elicited by GA3 and 2,2-dimethyl GA4, respectively. These results extend the differences in GA structure which favour flowering as opposed to stem elongation, and indicate that 3-hydroxylation and its epimeric configuration are of much greater importance to stem elongation than to flower initiation in Lolium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198703
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  • 3
    Electronic Resource
    Electronic Resource
    The differential effects of C-16,17-dihydro gibberellins and related compounds on stem elongation and flowering in Lolium temulentum (1994)
    Springer
    Planta 193 (1994), S. 107-114 
    Details
    ISSN: 1432-2048
    Keywords: Lolium ; Gibberellin ; Flowering ; Day-length ; Stem elongation ; 16,17-dihydro gibberellins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plants of Lolium temulentum L. cv. Ceres grown under short days (SDs) can be induced to initiate inflorescences either by exposure to one long day (LD) or by single applications of some gibberellins (GAs), which also enhance the flowering response to one LD. Single doses of up to 25 μg per plant of C-16, 17-dihydro-GA5 were about as effective as GA5 for promoting flowering after one LD but inhibited stem elongation by up to 40% over three weeks. The promotion of flowering but not the inhibition of elongation by 16, 17-dihydro-GA5 was reduced in SDs or in LDs low in far-red (FR) radiation. With shoot apices cultured in vitro, 16, 17-dihydro-GA5 was more florigenic than GA3 for apices excised after one LD of 14 h or more, but less florigenic for apices excised from plants in shorter days. 16, 17-Dihydro-GA5 was ineffective compared with GA1, GA3 and GA5 for α-amylase production by half-seeds of Lolium, a response concordant with its effect on stem elongation. As with GA5, 16, 17-dihydro derivatives of GA1, GA3, GA20 and several other GAs were more effective for flowering and less effective for stem elongation than the GAs from which they were derived. Hydroxylation at C-17 and/or C-16 generally reduced the effectiveness of 16, 17-dihydro-GA5 for flowering. These results extend the known features of GA structure which favour flowering relative to stem elongation in L. temulentum. Moreover, C-16, 17-dihydro-GA5 mimics, in its daylength- and wavelength-dependence and lack of stem elongation, characteristics of the LD stimulus in L. temulentum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191613
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  • 4
    Electronic Resource
    Electronic Resource
    Light requirement, phytochrome and photoperiodic induction of flowering of Pharbits nil Chois (1978)
    Springer
    Planta 141 (1978), S. 9-14 
    Details
    ISSN: 1432-2048
    Keywords: Flowering ; Pharbitis ; Photoperiodic induction ; Phytochrome ; Spectrophotometry (phytochrome)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The low chlorophyll content of cotyledons of Pharbitis nil grown for 24 h in far-red light (FR) or at 18° C in white light from fluorescent lamps (WL) allows spectrophotometric measurement of phytochrome in these tissues. The Δ(ΔA) measurements utilize measuring beams at 730/802 nm and an actinic irradiation in excess of 90 s. The constancy of the relationship between phytochrome content and sample thickness confirms that, under these conditions of measurement, a true maximum phytochrome signal was obtained. These techniques have been used to follow changes in the form and amount of phytochrome during an inductive dark period for flowering. Following exposure to 24h WL at 18° C with a terminal 10 min red (R), Pfr was lost rapidly in darkness and approached zero in less than 1 h; during this period there was no change in the total phytochrome signal. Following exposure to 24 h FR with a terminal 10 min R, Pfr approached zero in 3 h, and the total phytochrome signal decreased by about half. The relevance of these changes to photoperiodic time measurement is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387737
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  • 5
    Electronic Resource
    Electronic Resource
    Light requirement, phytochrome and photoperiodic induction of flowering of Pharbitis nil Chois (1978)
    Springer
    Planta 141 (1978), S. 1-7 
    Details
    ISSN: 1432-2048
    Keywords: Flowering ; Pharbitis ; Photomorphogenesis ; Photoperiodic induction ; Phytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract For dark-grown seedlings of Pharbitis nil capacity to flower in response to a single inductive dark period was established by 24 h white, far-red (FR) or ruby-red (BCJ) light and by a skeleton photoperiod of 10 min red (R)-24 h dark-10 min R. FR alone was ineffective without a brief terminal (R) irradiation, confirming that the form of phytochrome immediately prior to darkness is a crucial factor for flowering in Pharbitis. The magnitude of the flowering response was significantly greater after 24 h FR or white light (WL) (at 18° C and 27° C) than after two brief skeleton R irradiations, but the increased flowering response was not attributable to photosynthetic CO2 uptake because this could not be detected in seedlings exposed to 24 h WL at 18° C. Photophosphorylation could have contributed to the increased flowering response as photosystem I fluorescence was detectable in plants exposed to FR, BCJ, or WL, but there were large differences between flowering response and photosystem I capacity as indicated by fluorescence. We conclude that phytochrome plays a major role in photoresponses regulating flowering. There was no simple correlation between developmental changes, such as cotyledon expansion and chlorophyll formation during the 24-h irradiation period, and the capacity to flower in response to a following inductive dark period. Changes in plastid ultrastructure were considerable in light from fluorescent lamps and there was complete breakdown of the prolamellar body with or without lamellar stacking at 27 or 18° C, respectively, but plastid reorganization was minimal in FR-irradiated seedlings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387736
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