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1.
Abstract— The kinetics of phytochrome phototransformation from the red-absorbing form (Pr ) to the far-red-absorbing form (Pfr ) in vivo at 22°C were studied using a double flash apparatus with 1-ms flashes. Photoconversion by simultaneous flashes of red light saturates at a low Pfr level, indicating the possible attainment of a photoequilibrium between the excitation of Pr and the photoreversion of intermediates in the course of the I-ms flashes. At saturation energy, simultaneous flashes resulted in about 50% as much Pfr as was produced by saturating irradiation with 5 s red light. Intermediates of the phototransformation pathway were analysed by separating two red or a red and a far-red flash by variable dark intervals. In both plants phototransformation intermediates with half-lives < 1 ms occur, but they are too short-lived to characterize by our method. The subsequent intermediates have half-lives of about 7 ms and 150 ms in A vena , 2 ms and 10 ms in Mougeotia. The conversion from Pr to Pfr seems to be completed 1 s after the red flash in Avena. In the alga Mougeotia , Pfr formation seems to be finished within only 50 ms after the inducing red flash. The kinetics obtained from physiological and spectrophotometric experiments with Avena mesocotyls are almost identical. These observations indicate that the physiological response corresponds directly to the amount of Pfr produced and not to phototransformation intermediates or "cycling" between Pr and Pfr . 相似文献
2.
Abstract— Slow destruction of the far-red-absorbing form of phytochrome (Pfr ), which has been observed in light-grown oat and maize, occurs in light- and dark-grown Amaranthus, Pharbitis , and Brassica seedlings as well. Destruction of Pfr in these seedlings shows two phases: if a high level of Pfr is produced in dark-grown seedlings, the destruction is fast in the beginning and then slows after a low Pfr level has been reached. Slow Pfr destruction is predominant in light-grown tissue. 相似文献
3.
Abstract— Irradiation of the Pr form of phytochrome in the presence of flavin mononucleotide (FMN) which absorbs the actinic blue light yields Pfr at a rate greater than that in the absence of FMN. The actinic blue light absorbed by FMN enhances the phototransformation of Pr via the energy transfer from the former to the latter. On the other hand, the photoreversion of Pfr was inhibited by the presence of FMN when illuminated with blue light. The lack of photo-enhancement of the reversion of Pr , by blue light suggests that the Pfr chromophore (acceptor) transition dipole is virtually perpendicular to the FMN transition dipole, as the result of a chromophore reorientation in the Pr →Pfr phototransformation. The fact that blue light absorbed by flavin preferentially enhances the forward phototransformation of phytochrome while inhibiting the reversion may have an important implication in the high irradiance responses in plants in terms of a preferential accumulation of Pfr by blue light excitation. 相似文献
4.
Abstract— In epicotyl tissue of Pisum , irradiation of Pr at – 196°C forms a stable product P698 , whereas Pfr forms a stable product P650 . On warming P698 , dark transformation to Pr predominates. On warming P650 to – 70°C an intermediate P690 is formed which bleaches on further warming to –10°C. When tissue is cooled to –196°C during actinic irradiation, difference spectra for subsequent warming to –10°C indicate that Pr , Pfr and an intermediate P710 are formed from weakly absorbing intermediates. Complete photoconversion of Pr to Pfr is not possible at temperatures below –5°C. As the temperature is reduced, the amount of Pfr produced from Pr decreases, while P710 increases. P710 can be photoconverted at –20°C and above, ultimately forming Pr , but in contrast to Pfr it is not photoconvertible at –196°C. 相似文献
5.
Abstract— Not only the spectral distribution of the light source determines the relative proportion of phytochrome in the Pfr (Pr ) form, the Pfr /Ptot -ratio also depends strongly on the fluence rate of the irradiation. This dependence has been observed in the cotyledons of etiolated mustard seedlings for blue light of fluence rates below 20 Wm-2 . It has also been observed for white light and seems to be a characteristic of the phytochrome system resulting from the involvement of phytochrome thermal reactions as well as Pr Pfr photoconversions. The fluence rate dependence of Pfr /Ptot -ratios can be used to analyze the characteristic transformations of the phytochrome system. Phototransformations together with a fast thermal transformation (τ½ ⋍ 3min) are consistent with the results obtained for blue and white light. 相似文献
6.
Rodger D. Scurlock Silvia E. Braslavsky Kurt Schaffner 《Photochemistry and photobiology》1993,57(4):690-695
Abstract— The phototransformation of native (124 kDa)oat phytochrome, Pr Pfr , Has been studied at 10C by two laser/ two-color flash photolysis. the overall Pr Pfr reaction yield did not vary with temperature within the range4–21C. Foloeing the excitation of Pr with a single 15 ns laser flash at 650nm, the formation of Pfr was quantitavely measured in a time-resolved experiment in the presence of a second 8 ns laser flash at 710 nm delayed from the initial flash. the second laser flash causes at 1.0 s after the initial laser flash a depletion of the uintermediate I700 as welll as a reduction of the Pfr absorption at 730 nm. The depletion of I700 correlates quantitavely with the reduction of Pfr formation. The absorpton spectra of I700 and of the following intermendiate, Ibi , were calculated assuming that the amount of Pr , which is photoconverted by a single laser, equals the amount of Pfr formed. 相似文献
7.
PHYTOCHROME INTERMEDIATES IN VIVO– III KINETIC ANALYSIS OF INTERMEDIATE REACTIONS AT LOW TEMPERATURE
Abstract— Kinetic experiments have provided evidence for a series of light and dark reactions of phytochrome intermediates at low temperature in Pisum epicotyl tissue. A photoequilibrium exists between Pr and P698 , and between Pfr and P650 . A dark reversion of P698 Pr and P650 pfr at –70°C has been demonstrated. When cooled to 70°C under incandescent light, most of the phytochrome in the tissue is driven into photochemically unreactive intermediates. About 2% of the phytochrome remains as weakly absorbing intermediates that form Pr and Pfr in darkness. A scheme is presented for phytochrome phototransformation in vivo. 相似文献
8.
Tohru Sugimoto Yasunori Inoue Hideo Suzuki Masaki Furuya 《Photochemistry and photobiology》1984,39(5):697-702
Abstract— The changes in the chromophore structure of pea phytochrome during phototransformation in vitro from the red-light-absorbing form (Pr ) to the far-red-light-absorbing form (Pfr ), and from Pfr to Pr , were analysed in terms of wavelength and oscillator strength of absorption, using the zero-differential overlap approximation of the molecular orbital theory for electrons. The effect of a point-charge and a point-dipole on the optical absorption of phytochromobilin intermediates were examined using the stationary perturbation theory for degenerate states. The results indicate that the cis-trans photoisomerization of the pyrrole ring D, if any, occurred within 10 μs after a laser-flash excitation of the phytochrome, and that the conformations of phytochromobilin and the protein moiety of phytochrome were not significantly changed during the period of examination of phototransformation in either direction. 相似文献
9.
MODE OF COACTION OF PHYTOCHROME AND BLUE LIGHT PHOTORECEPTOR IN CONTROL OF HYPOCOTYL ELONGATION 总被引:4,自引:0,他引:4
Abstract The rate of hypocotyl longitudinal growth in seedlings of Sesamum indicum L. is strongly inhibited by continuous blue light (cBL)† and slightly by continuous far-red light while continuous red light (cRL) or red light pulses are hardly effective from 60 h after sowing onwards. Between 36 and 60 h after sowing the growth rate responds to red light pulses the effect of which is fully reversible by long wavelength far-red light. When seedlings are kept in cBL for 3 days and then treated with red light hypocotyl growth rate responds strongly. However, RL effectiveness decreases with time after transfer from BL to RL. BL → darkness transfer experiments with different levels of Pfr established at the beginning of darkness show that after a BL pretreatment phytochrome (Pfr ) alone is capable of fully controlling growth rate. When white light (WL) is given no BL effect is detectable in weak WL. Only high light fluxes maintain a typical BL growth rate. At medium WL fluxes elongation rate returns gradually to the dark rate. The simplest explanation of the data is that light absorbed by a separate BL photoreceptor is necessary to maintain responsivity to Pfr . With increasing age of the seedlings the requirement for BL increases strongly. On the other hand, brief light pulses—given to demonstrate photoreversibility of phytochrome—remain equally effective provided that responsivity to Pfr exists. 相似文献
10.
Silvia E. Braslavsky † J. Ioan Matthews † Hans J. Herbert † Jacob de Kok† Carel J. P. Spruit Kurt Schaffner† 《Photochemistry and photobiology》1980,31(4):417-420
Abstract— Irradiation of small phytochrome from oat in its Pr form with 15 ns laser pulses of different wavelengths(605–655 nm) gave rise to a difference absorption with maxima at 400 and 685 nm for the first detectable transient. Bleaching of a 660 nm band was observed, non-recuperable up to 1 ms. The transient absorption has a lifetime of 70±15 μs at 273 K. The transient is tentatively identified as lumi-R and the conformation of its chromophore is postulated to be more extended than that of Pr . A deviation from the exponential decay of the lumi-R absorption at 284 and 300 K and the lack of observable enhancement of the far-red absorption within 1 ms are interpreted in terms of the appearance of still other intermediates on this time scale between lumi-R and Pfr phytochrome. 相似文献
11.
ON THE PHYSIOLOGICAL SIGNIFICANCE OF DARK REVERSION OF PHYTOCHROME IN THE MUSTARD SEEDLING 总被引:1,自引:0,他引:1
Abstract —We present physiological evidence using the threshold control of lipoxygenase synthesis† by Pfr in the mustard seedling (LOG response) that there is no dark reversion of phytochrome
which would be relevant for this response. Such Ptr which can be detected with the lipoxygenase response disappears exclusively through degradation with a half-life of 45 min at 25°C. De novo synthesis of P*r in the hypocotylar hook takes place at a constant rate (zero order rate constant) irrespective of the level of Pr or P*tot , i.e. there is no detectable feedback control of Pr synthesis during the period of experimentation. The data of the present paper are consistent with a quantitative phytochrome model (Scheme 1) which has been advanced and treated quantitatively in the companion paper (Oelze-Karow and Mohr, 1976). 相似文献
which would be relevant for this response. Such Ptr which can be detected with the lipoxygenase response disappears exclusively through degradation with a half-life of 45 min at 25°C. De novo synthesis of P*
12.
In the blue spectral region, the phototransformation difference spectrum of oat phytochrome extracted as Pfr differs from that of phytochrome extracted as Pr . The difference absorbance maximum for phytochrome extracted as Pfr is at 420 nm, while that extracted as Pr is at 412 nm. The phototransformation difference spectrum measured in the blue in oat coleoptile tips without inner leaves, corresponds very well with that of phytochrome as extracted in its Pfr form. There is, however, a slight apparent attenuation of the blue difference band relative to those in the red-far-red. In coleoptile tissue containing inner leaves, the blue difference band is relatively even more highly attenuated. A similar attenuation is observed in the blue, in the protochlorophyllide to chlorophyllide phototransformation difference spectrum. In the spectrum measured with excised coleoptile without inner leaves, there is a small attenuation, while in coleptile tissue with inner leaves the attentuation is nearly 9-fold. These data suggest that the observed attenuation is probably artifactual. Neither instrumental non-linearity nor fluorescence induced by the measuring beam could explain the observed attenuation. It is suggested that the observed attenuation is probably mainly the result of wavelength dependent scatter amplification, the amplification in the blue being attenuated by the high background absorption of other pigments in this region. 相似文献
13.
Thomas Brandlmeier Harald Lehner Wolfhart Rüdiger† 《Photochemistry and photobiology》1981,34(1):69-73
Abstract— The circular dichroism spectra of oat phytochrome were recorded. Qualitatively, the same spectra were found for large (360 kilodaltons) and small (60 kilodaltons) phytochrome. Quantitative CD data were reported for small Pr and Pfr (photoequilibrium mixture with 20% Pr ) in tris buffer (native state) and in acid urea (denatured state). Further, the CD spectra of a phytochromobilinpeptide in acid solution with and without urea were recorded. Differences between the data in native and denatured state are discussed. 相似文献
14.
COMPARATIVE PHOTOCHEMICAL ANALYSIS OF HIGHLY PURIFIED 124 KILODALTON OAT and RYE PHYTOCHROMES in vitro 总被引:3,自引:0,他引:3
J. Clark Lagarias John M. Kelly Karen L. Cyr William O. Smith Jr 《Photochemistry and photobiology》1987,46(1):5-13
Abstract A direct comparison of the photochemical interconversions between red (Pr -) and far-red (Pfr -) absorbing forms of highly-purified 124 kDa oat and rye phytochromes under identical experimental conditions was performed. In two different buffer systems at 5°C, the quantum yields for the Pr to Ptr and Pfr to Pr phototransformations under constant red and far-red illumination, φ r and φfr respectively, were determined to be 0.152-0.154 and 0.060-0.065 for oat preparations and 0.172-0.174 and 0.074-0.078 for rye preparations. These values as well as the wavelength dependence of the photoequilibrium produced under continuous illumination throughout the visible and near-ultraviolet spectrum were based on the absorption spectra of the two phytochrome preparations and revised molar absorption coefficients. The molar absorption coefficients were estimated by quantitative amino acid analysis and shown to be identical for the two monocot phytochromes (i.e. 132 mM −1 cm−1 at the red absorption maximum for the Pr form). Because these measurements were performed under identical experimental conditions, including buffer, temperature, light fluence rate, and instrumentation, the differences observed must reflect structural features inherent to the two different monocotyledonous phytochromes. 相似文献
15.
CONTROL BY PHYTOCHROME OF EXTENSION GROWTH and POLAROTROPISM IN CHLORONEMATA OF Funaria hygrometrica
Abstract— The photocontrol of extension growth and polarotropism has been investigated in chloronemata of the moss Funaria hygrometrica Hedw. When grown on a 12/12 h light/dark cycle, chloronemata show light-stimulated diurnal variations in elongation rate with no evidence of a circadian rhythm. Regulation of elongation by a low energy, photoreversible phytochrome mechanism was demonstrated by brief red (R) and far red (FR) irradiations given either at the end of the day (EOD) or 6 h later as a night break (NB). Night break irradiation with polarised R caused polarotropic reorientations of chloronemal growth also through a FR-reversible, low energy phytochrome mechanism. Such transformations of Pr to Pfr were accompanied by a 90° shift in the orientation of the phytochrome chromophore. Microbeam irradiation indicated that the phytochrome chromophores involved in both responses were predominantly, if not entirely, located in the tip of the apical chloronemal cell. 相似文献
16.
The dichroic orientation of phytochrome observed both in the phytochrome-mediated phototropism in Adiantum protonemata and in the phytochrome-mediated chloroplast movement in Mougeotia were analyzed in terms of the orientation of the transition moment associated with the long-wavelength absorption band, assuming that phytochrome, associated with the plasma membrane, rotates around the normal to the membrane. The orientation of the long-wavelength transition moment of the phytochrome chromophore was calculated using the zero-differential overlap approximation of the molecular orbital theory for ir-electrons. The results indicate that the orientation of the long-wavelength transition moment mainly changes later than 2 ms after red light excitation of Pr , and that the different dichroic orientations of Pr and Pfr can be attributed to the change in the angle of the long-wavelength transition moment of phytochrome with the plasma membrane from 18o to 72o during phototransformation. 相似文献
17.
Hypocotyl elongation in mustard (Sinapis alba L.) seedlings is known to be controlled by phytochrome (Pfr ) through a threshold response. This phytochrome-mediated threshold response was studied in detail with the following results: (i) The Pfr threshold value required to suppress hypocotyl growth is much lower (0.03% Prr , based on total phytochrome in the hypocotyl at 36 h after sowing = 100%) than those threshold valued observed previously in threshold control by hook phytochrome of appearance of 'potential capacity for photophosphorylation' and lipoxygenase appearance in the mustard cotyledons (1.25% Ptr , based on total phytochrome in the hypocotyl at 36 h after sowing = 100%). This probably explains why hypocotyl elongation is so extremely sensitive to light, (ii) The Pfr threshold value controlling hypocotyl growth is a system constant, independent of total phytochrome content, developmental age and actual growth rate, (iii) Threshold control of hypocotyl elongation is unaffected by the removal of the cotyledons and half of the hook. However, removal of the whole hook totally eliminates any light control over the residual hypocotyl growth, (iv) After termination of the threshold control, the hypocotyl growth rate immediately returns to precisely that found in untreated dark control even though the partial growth rates of the different parts of the hypocotyl are quite different, relative to their dark controls. Obviously, the organ grows as an integrated unit.
It is concluded that the all-or-none threshold control over hypocotyl growth is exerted from the plumular hook. It appears that the hook can send off phytochrome all-or-none signals in both directions, to the cotyledons and to the hypocotyl. 相似文献
It is concluded that the all-or-none threshold control over hypocotyl growth is exerted from the plumular hook. It appears that the hook can send off phytochrome all-or-none signals in both directions, to the cotyledons and to the hypocotyl. 相似文献
18.
Abstract— The phototransformation of phytochrome ( Pr ) to its physiologically active form (Pfr ) can be best described by a tautomeric proton shift in ring A without a substantial con formational change of the chromophore. The electronic aspect of this transformation is discussed. 相似文献
19.
Abstract— The photooxidation of octaethyl-2, 3-dihydrobilindione ( 2 ) as a model for the Pr -chromophore has been studied in acidic methanol. When 2 is titrated with HCl to the cation and irradiated under N2 with an excess of I2 , violin and rhodin type pigments are formed bearing methoxy-substituents at either C-4,5 or C-15,16, respectively. The reaction is slowed down as compared to neutral conditions, it is no longer regioselective at the C-5 methine bridge, and the formation of dimers is suppressed. From the data of this and earlier chemical model studies on the photooxidation of 2 , and the known properties of phytochrome, a reaction for the Pr → Pfr phototransformation is suggested, in which the chromophore is attacked by the protein moiety in a sequence of oxidation and nucleophilic substitution, which may lead to a primary redox signal for the physiological response. 相似文献
20.
PHYTOCHROME INTERMEDIATES IN VIVO-I. EFFECTS OF TEMPERATURE, LIGHT INTENSITY, WAVELENGTH AND OXYGEN ON INTERMEDIATE ACCUMULATION 总被引:3,自引:0,他引:3
Abstract— Accumulation of weakly absorbing phytochrome intermediates has been demonstrated in Pisum epicotyl tissue under conditions of pigment cycling using a quasi-continuous measuring spectrophotometer. An action spectrum shows 690–700 nm to be the most efficient wavelength range in this process. Difference spectra for the decay of intermediates maintained by 690 nm light show that, if the experiment is done at 0°C, only Pfr is formed. At – 11°C, intermediates decaying to Pr can also be observed. At – 20°C, Pr is produced as well as a pigment with peak absorption at 710nm. Kinetic analysis of intermediate decay at – 11°C reveals that at least two intermediates are maintained by 690 nm light. The level of intermediate maintained by incandescent light at 0°C was 25% higher in air than in nitrogen. 相似文献