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1.
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
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C. J. P. Spruit 《Photochemistry and photobiology》1982,35(1):117-121
Abstract— Rate constants for the formation of Pfr , the far-red-absorbing form of phytochrome, from photochemical intermediates, have been measured in vivo in a number of plants. Two first order processes were observed, the slowest of which has been studied in detail. In pea epicotyl hooks, the rate constants proved dependent on temperature as well as on composition of the gas phase. A transition point was observed at about—2°C. Above this temperature the Arrhenius activation energy is 61 ± 6 kJ/mol, below the transition temperature 200 + 17 kJ/mol. The data correspond to half lives of between 0.4 and 0.2 s in an atmosphere of oxygen at 20°C, depending upon the species of plant. In oxygen-free atmospheres, the rates are between 1.7 and 1.9 times as fast. The data prove that, on the time scale relevant to the usual type of photomorphogenetic experiments, the occurrence of phytochrome intermediates generally can be neglected. Exceptions to this generality are formed by experiments involving continuous or very rapidly intermittent exposures to very high light intensities. Under these conditions the steady state fraction of Pfr may be considerably lower than calculated from the spectroscopic data for the pigment and the light sources. 相似文献
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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
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A photodelay in chlorophyll- a and -b accumulation is observed in mustard ( Sinapis alba L.) cotyledons during the first 3 h after the onset of white light even at medium light fluxes (3500 lx). A pretreatment of two red light pulses or a 12 h far-red light pretreatment, both operating through phytochrome. prevent the photodelay completely. This is a specific phytochrome effect since'it can be separated from the effects of phytochrome on the rates during pre-steady state and steady state phases of chlorophyll accumulation in saturating white light. Thus, photostability of chlorophyll in nature is a photoresponse mediated through phytochrome. 相似文献
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以含磷较低的铁合金作底液,以钼酸铵为显色剂,用磷钼蓝光度法测定铁合金中的磷。磷钼蓝的摩尔吸光系数为7.8×10~5L/(mol·cm),与磷钼黄光度法、氟化钠-氯化亚锡还原磷钼蓝光度法相比,测定灵敏度有不同程度的提高。该方法用于实际样品分析,结果准确、可靠。 相似文献
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LEE H. PrattYukio SMMAZAKIT†Yasunori Inoue†Masaki Furuya† 《Photochemistry and photobiology》1982,36(4):471-477
Phototransformation of the red-absorbing form of phytochrome (Pr) to the far-red-absorbing form (Pfr) was followed with a custom-built transient spectrum analyzer. Large phytochrome, which consisted of approximately 120000-dalton monomers, was immunopurified or conventionally purified from etiolated oat (Avena sativa L., cv. Garry) shoots. Phototransformation was initiated by exciting Pr with a 115-mJ, 600-ns half-width, 655-nm laser pulse. Absorption spectra were recorded on a microsecond time scale at predetermined times after the flash. It has been reported earlier that flash excitation of large oat Pr produces a transformation intermediate with maximum absorbance near 700 nm in a difference spectrum and that this intermediate decays by two kinetically distinct reactions. Difference spectra for these two reactions are indistinguishable. Both show bleaching centered at 690 nm with no detectable associated absorbance increase between 570 and 830 nm. Subsequent appearance of absorbance at 724 nm, which presumably but not necessarily represents the appearance of Pfr, had earlier been shown to occur by two kinetically distinct reactions for large oat phytochrome. Data presented here indicate in addition the occurrence of a third, slower reaction. Difference spectra for the two faster reactions are indistinguishable, both with maxima near 728 nm and minima near 650 nm. The difference spectrum for the slowest component, however, was qualitatively different exhibiting a maximum near 722 nm with no corresponding minimum. About 15-20% of the absorbance increase at 724 nm occurred by this slowest reaction, which exhibited a half-life of 3 s at 25°C and a Q10 of 1.2 for immunopurified and 1.5 for conventionally purified phytochrome. The percentage occurring by this reaction was independent of temperature over the range studied (1-25dEC). For immunopurified phytochrome the enthalpy of activation, Gibbs free energy of activation, and entropy of activation of this slowest reaction were found to be about lOkJ-mol-1, 75kJ.mol-1, and -220 J.mol-1 K-1, respectively, and for conventionally purified phytochrome 25kJ.mol-1, 75kJ.mol-1and —170 J.mol-1 K-1, respectively. The thermodynamic characteristics of this reaction indicate that it may involve a significant ordering of the protein moiety as it transforms to Pfr. 相似文献
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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
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A custom-built modulated split-beam spectrophotometer has been used to measure the absorbance of tissue samples and purified phytochrome whilst exposing the sample to actinic 633 nm laser radiation at fluence rates approaching those of daylight. This approach has allowed the direct observation of the accumulation of phytochrome photoconversion intermediates at high fluence rates. At ca 1250 μmol m?2 s?1 upwards of 35% of the total phytochrome was present in the form of photoconversion intermediates in tissues of maize, sunflower and tomato. In other tissues tested (wheat, bean and Amaranthus) and in purified oat phytochrome, rather smaller levels of intermediates accumulated. Upon “lights-off” only a proportion of the accumulated intermediates decayed to far-red absorbing phytochrome (Pfr), the remainder appearing as the red-absorbing form (Pr). Difference spectra suggested that, at high light levels, Pr may be reformed via a photochemical back-conversion of an intermediate in the Pr—Pfr pathway, although the involvement of intermediates in the Pfr—Pr pathway cannot be excluded. The implications of the results for the ecological function of phytochrome are discussed. 相似文献
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Abstract— In vitro phosphorylation of some polypeptides was affected in extracts obtained from 5-and 6-day-old plants irradiated with 5 min of red light. The phosphorylation of 55 kDa polypeptide in both 5- and 6-day-old plants, a 60 kDa, and 76 kDa polypeptide in 6-day-old plants and 70 kDa, 67 kDa polypeptide in 5-day-old plants was stimulated by red light. This effect was reversible by far-red light. The extent of stimulation by red light and reversal by far-red light varied for different polypeptides. No differential effect of red and far-red light was seen on the phosphorylation of 94 and 40 kDa polypeptides. In fact, phosphorylation of 94 kDa polypeptide in 6-day-old plants decreased on red light irradiation. These results show that the phosphorylation or dephosphorylation of some proteins is affected by phytochrome and the effect of light is also dependent on the age of the plant. 相似文献
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Abstract— Phototransformation from the red-absorbing form of phytochrome (Pr) to the far-red-absorbing form occurs via at least two reaction stages. We report here on the photoactivity of the intermediates present during these two stages, as detected with 114/118-kdalton Avena phytochrome by a transient spectrum analyzer with two actinic lasers of microsecond duration. Flash activation of intermediates present during the first stage results in their photoconversion back to Pr within the time resolution provided by the analyzer, which is 10 μs. Since these intermediates are present within 60 ns of excitation of Pr (Cordonnier et al. , 1981), a single flash of ms duration as used here should yield a photostationary equilibrium between them and Pr. The proportion of Pr converted to intermediates by a single saturating flash is estimated to be about 30%. Flash activation of intermediates present during the second stage converts them to another transient intermediate stage, which decays thermally to Pr within 2 ms. 相似文献
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THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—III. MEASUREMENT AND CALCULATION OF PHYTOCHROME PHOTOEQUILIBRIA 总被引:1,自引:0,他引:1
Abstract— Phytochrome photoequilibria have been measured in dark-grown Phaseolus uulgaris L . and Cucurbita pepo I . hypocotyl hooks which had been exposed to various natural and artificial radiation sources. Mean phytochrome photoequilibria ( φ ) varied from 0.20 within a wheat canopy to 0.54 above, although lower values were occasionally observed in densely shaded areas. Greater variation in phyto chrome photoequilibria and lower levels of Pfr were recorded within a sugar beet canopy. The range of photoequilibria was φ= 0.04 in dense shade to φ= 0.54 above the canopy. Photoequilibrium was achieved within 5 s in mid-day sunlight and approximately 30 s in dense canopy shade.
A close correlation was found between φ and the ratio of the quantum flux in the red and far-red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.
The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants. 相似文献
A close correlation was found between φ and the ratio of the quantum flux in the red and far-red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.
The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants. 相似文献
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The strong effect of light pretreatments on the synthesis of chlorophyll-a and-b in the shoot of Sorghum vulgare (kept under saturating white light) can be attributed to phytochrome only. No specific blue light effect was found. The phytochrome system appears to function perfectly normally under these conditions. Escape from reversibility is not detectable up to approximately 40 min after the onset of an inductive red light pulse. Thereafter, escape is fast, being completed at approximately 2.5 h after the inductive light pulse. 相似文献
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Abstract— The yellow color of 9,10-phenanthrenequinone in alcohol solution is bleached under the influence of exciting radiation in a band of wavelengths extending from the ultraviolet to the visible green. The bleaching is due to a photoreduction of the quinone yielding 9,10-dihydroxyphenanthrene. In the presence of certain divalent metal ions, irradiation of the quinoid material results in a blue-green long lived intermediate which may be further photo-reduced to the colorless 9,10-diol. The blue-green photo-intermediate is a cation-semiquinone complex. 相似文献
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分光光度法测定铝合金中锰的不确定度评定 总被引:1,自引:0,他引:1
对分光光度法测量铝合金中锰含量的测量不确定度进行评定,分析了测量过程中不确定度的主要来源,如测量重复性、溶液浓度、溶液体积、试样溶液定容体积、分取溶液体积等,并对各不确定度分量进行了量化.对锰含量为0.80%~2.00%的铝合金,置信水平为95%时,测量结果的扩展不确定度为0.02%. 相似文献