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1.
INDUCTION OF LEAF UNROLLING BY PHYTOCHROME and ACETYLCHOLINE IN ETIOLATED WHEAT SEEDLINGS 总被引:1,自引:0,他引:1
Abstract-Phytochrome regulates the unrolling of primary leaf sections from 8-day-old dark-grown wheat ( Triticum aeslivum L. cv. Arminda) seedlings. Red light (R)-stimulated unrolling of leaf sections pretreated in 1 m M ethylene-bis-(β-aminoethylether)- N,N,N',N' -tetraacetic acid (EGTA) if 1 m M CaCl2 was added during a 30 min treatment period including and following irradiation. Nifedipine at 1 μ M (a Ca2 +-channel antagonist) applied 10 min before R prevented the R stimulation of leaf unrolling. The Ca2 +-channel agonist Bay K-8644 (1 μ M ) and acetylcholine (ACh, 1 mY M ) stimulated unrolling of leaf sections prewashed in EGTA in darkness, if 1 m M CaCl2 was present in the medium during a 30 min treatment period. Acetylcholine also induced leaf unrolling in the absence of Ca2 + when 100 μ M NaCl was present in the medium. Apart from ACh, only carbamylcholine out of the choline derivatives tested was active in induction of leaf unrolling in the presence of 1 m M Ca2 +. The ACh receptor antagonists, atropine (10 μ M ) AND D-tubocurarine (10 μ M ), nullified the ACh-induced Ca2 +- and Na+-dependent leaf unrolling, respectively. Muscarine and nicotine, agonists of ACh, at 1 μ M stimulated leaf unrolling in the presence of Ca2 + and Na+, respectively. The ACh-induced Ca2 +-dependent leaf unrolling was reduced by 1 μ M Nifedipine, 10 μ M Li+ and 10 μ M "calmodulin" inhibitor, trifluoperazine (TFP), whereas only TFP was active in the reduction of the Na+-dependent ACh-induced leaf unrolling response. It is proposed that leaf unrolling of dark-grown primary wheat leaves can be regulated by phytochrome and by activation of two different types of ACh receptors. 相似文献
2.
NEAR-UV-INDUCED BREAKS IN PHAGE DNA: SENSITIZATION BY HYDROGEN PEROXIDE (A TRYPTOPHAN PHOTOPRODUCT) 总被引:7,自引:0,他引:7
Abstract— Near-UV irradiation of l -tryptophan yields a large number of photoproducts. When this mixture is added to recombinationless ( rec ) mutants of bacteria, the cells are killed. The most toxic component of tryptophan photoproducts has been identified as hydrogen peroxide (H2 O2 ). We now report that both tryptophan photoproducts and H2 O2 sensitize phage DNA to near-UV radiation resulting in enhanced killing as well as enhanced DNA breakages. We conclude that the in situ production of H2 O2 via tryptophan photolysis may be an important biological event. 相似文献
3.
ACTION OF HYDROGEN PEROXIDE ON HUMAN FIBROBLAST IN CULTURE 总被引:6,自引:0,他引:6
Abstract— Human fibroblasts in culture lose the capacity of proliferating when exposed to hydrogen peroxide in the concentration range of 1 to 10 μ M . The toxicity of H2 O2 to xeroderma pigmentosum cells (XP12RO). defective in excision repair of lesions produced by UV-irradiation, was about twice as high as to cells proficient in excision repair (VA13). This compound produces single-strand breaks in intracellular DNA but not in purified DNA. These breaks are in situ physical discontinuities rather than alkali-labile bonds, and their generation occurs at the same extent at 4°C and 37° indicating that they are not produced by an endonuclease. The results favor the hypothesis that H2 O2 reacts in the cell producing a radical species which brings about the formation of DNA single-strand breaks. These breaks are effectively repaired by both XP12RO and VA13 fibroblasts. The possible reason for the lethality of H2 O2 is discussed. 相似文献
4.
Abstract —In vivo participation of singlet excited oxygen (1 O2 , 1 Δ9) in the photodynamic inactivation and induction of genetic changes (gene conversion) in acridine orange-sensitized yeast cells was investigated by using N3 - , an efficient 1 O2 quencher, and D2 O, a known agent for the enhancement of the lifetime of 1 O2 . The addition of N3 - protected the cells from both photodynamic actions. From an analysis of the concentration-dependent protection, about 80% of the induction of the genetic change is explainable on the basis of 1 O2 mechanism. The quantitative estimation of the N3 - protection in the inactivation was not possible because of the sigmoidal nature of the inactivation curve. The replacement of H2 O with D2 O during illumination was effective in enhancing the photodynamic inactivation but almost completely ineffective for the gene conversion induction. The deuterium effect with the cell system was clearly not as large as would be expected from in vitro experiments. This, however, could be explained from the kinetic consideration that natural quenchers of l O2 in the cell would mask the deuterium effect. By experiments with different cell stages it was demonstrated that these two modifying effects were dependent on the intracellular reaction environment. The conclusion is that 1 O2 must be the major intermediate responsible for the photodynamic actions in acridine orangesensitized yeast cells. 相似文献
5.
COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION–I. A LINEAR FOUR STEP MECHANISM 总被引:30,自引:0,他引:30
Abstract— Using isolated chloroplasts and techniques as described by Joliot and Joliot[6] we studied the evolution of O2 in weak light and light flashes to analyze the interactions between light induced O2 precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents either as precursor or as O2 . 2. The number of unstable precursor equivalents present during steady state photosynthesis is ∼ 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final O2 evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, ( S ) successively accumulates four + charges. The S 4+ state produces O2 and returns to the ground state S 0 . 5. Besides S 0 also the first oxidized state S + is stable in the dark, the two higher states, S2+ and S3+ are not. 6. The relaxation times of some of the photooxidation steps were estimated. The fastest reaction, presumably S *1 ← S 2 , has a (first) half time ≤ 200 μsec. The S *2 state and probably also the S *0 state are processed somewhat more slowly (˜ 300–400 μsec). 相似文献
6.
Abstract— In view of the increasing attention to 1 O2 (1 Δg ) participation in the photodynamic action, different types of genetic changes in Saccharomyces cerevisiae by acridine orange sensitization were compared with respect to the response to N3 - , a well known quencher of 1 O2 . The induction of mitotic crossing over with respect to ade 2 locus and mitotic gene conversion at trp 5 locus were suppressed by the addition of N3 - suggesting the involvement of 1 O2 as a major intermediate. However, the induction of reverse mutation at ilv 1 was only slightly suppressed. These results may indicate that there are two types of photodynamic DNA damage; one is produced via 1 O2 and the other via non-1 O2 reaction pathway which lead to mitotic gene conversion and mitotic crossing over, and to mutation, respectively. 相似文献
7.
Ding Wang Thomas Oppenländer Mohamed Gamal El-Din James R. Bolton 《Photochemistry and photobiology》2010,86(1):176-181
The efficacy of UV and vacuum-UV (VUV) disinfection of Bacillus subtilis spores in aqueous suspensions at wavelengths of 172, 222 and 254 nm was evaluated. A Xe2 * excilamp, a KrCl* excilamp and a low-pressure mercury lamp were used as almost monochromatic light sources at these three wavelengths. The first-order inactivation rate constants at 172, 222 and 254 nm were 0.0023, 0.122 and 0.069 cm2 mJ−1 , respectively. Therefore, a 2 log reduction of B . subtilis spores was reached with fluences (UV doses) of 870, 21.6 and 40.4 mJ cm−2 at these individual wavelengths. Consequently, for the inactivation of B . subtilis spores, VUV exposure at 172 nm is much less efficient than exposure at the other two wavelengths, while exposure at 222 nm is more efficient than that at 254 nm, which is probably because triplet energy transfer from DPA to thymine bases at 222 nm is higher than that at 254 nm. This research indicated quantitatively that VUV light is not practicable for microorganism disinfection in water and wastewater treatment. However, in comparison with other advanced oxidation processes ( e.g. UV/TiO2 , UV/H2 O2 or O3 /H2 O2 ) the VUV-initiated photolysis of water is likely more efficient in generating hydroxyl radicals and more effective for the inactivation of microorganisms. 相似文献
8.
Abstract. A model was developed to describe changes in fluence-response kinetics in terms of total phytochrome level (Ptot ), level of the factor X interacting with active phytochrome (Pfr ), Pfr X equilibrium constant, seed sensitivity to Pfr -X interaction, and variation in phytochrome sensitivity within the seed population. Under conditions of stable X levels and stable population variation, the model predicted that a change in any of the other components will result in a parallel fluence-response curve on a probit-logarithmic plot. The linearity of the subsaturation plot is dependent on the ratio of Ptot to X concentrations. The model showed that changes in threshold response fluences can result from many causes other than changes in total phytochrome [Ptot> ]. Changes in response-saturating fluences when maximal germination is less than 100% are predicted to be due to limiting levels of X. Changes in slope of fluence-response curves can be explained by changes in seed population variation by this model. Rumex crispus L. fluence-response data for germination is best explained by this model in terms of neither changes in Ptot nor X levels altering kinetics. 相似文献
9.
Abstract— Previous work obtained from Chinese hamster V-79 cells indicated that, immediately following exposure, UV-induced lesions acted as blocks to elongation of nascent strands, but gradually lost that ability over a 10 h period after exposure to 10 J/m2 . The work reported herein attempted to examine possible cell cycle mediated alterations in the recovery of DNA synthesis. Kinetic incorporation of radiolabeled thymidine studies indicated that there may have been a more rapid recovery of DNA synthesis in cells irradiated in G1 or G2 vs cells irradiated in S phase. DNA fiber autoradiograms prepared from synchronous cells indicated that after irradiation in any phase of the cell cycle, the length of newly synthesized DNA was equal to control lengths 1 h after exposure to 5.0 J/m2 (or 1 h after entering S phase for cells irradiated in G1 or G2 ). This observed recovery was not solely due to an excision process. No cell cycle mediated difference in the number of dimers induced or removed as a function of cell cycle position was observed. These results appear to be consistent with a continuum of effects, with initiation effects dominating the response at low fluences, gapped synthesis at intermediate fluences and elongation inhibition at high fluences. The fluences at which each event dominates may be cell-line specific. 相似文献
10.
Abstract— Survival, UV-photoproducts and germination of UV-irradiated spores of Dictyostelium discoi-deum were studied on two strains,NC–4 andys–13. The spores ofNC–4 are about 35 times more resistant to UV thanys–13 spores at 10% survival. Pyrimidine dimers were formed in UV-irradiated spores in both strains. No photoproducts other than pyrimidine dimers were detected. The formation of pyrimidine dimers in spores was about 2% in both strains at 800 J/m2 . In the germination of spores, the conversion of spores into swollen spores was not affected by UV in both strains, but the emergence of amoebae from the swollen spores was suppressed, which was more distinctive inys–13 spores than inNC–4 spores. The emerged amoebae from the UV-irradiatedNC–4 spores were viable, while those from theys–13 spores were inviable even when they succeeded in emergence. 相似文献
11.
N. J. de Mol G. M. J. Beijersbergen van Henegouwen B. Weeda C. N. Knox T. G. Truscott 《Photochemistry and photobiology》1986,44(6):747-756
The photobinding of radiolabeled psoralen and 8-methoxypsoralen (8-MOP) to biological macromolecules under conditions that affect the lifetime of singlet oxygen (1 O2 ) is reported. These conditions are: increase of 1 O2 lifetime in D2 O and 1 O2 quenching with DABCO. The photobinding to calf thymus DNA was studied in vitro and the covalent photobinding to DNA and other biological macromolecules (RNA, proteins) was also studied in intact bacteria. The results of the DNA photobinding experiments have been related to the induction of genetic damage in a bacterial test system. In addition, laser flash photolysis has been used to measure the effect of D2 O and DABCO on the psoralen and 8-MOP triplet lifetimes. In general D2 O increases the triplet lifetimes and DABCO quenches the triplet states with the probable formation of radicals. The results suggest that the covalent photobinding of 8-MOP to various biological macromolecules in situ is a basis for cell damage occurring at various cellular targets. Analysis of the results of the mutagenicity test suggests that in the presence of D2 O the mechanism of induction of genetic lesions is not changed and therefore largely seems to be independent of singlet oxygen. 相似文献
12.
THE DOSE RESPONSE CURVE IN PHYTOCHROME-MEDIATED ANTHOCYANIN SYNTHESIS IN THE MUSTARD SEEDLING 总被引:6,自引:0,他引:6
Abstract —The dose response curve for light (phytochrome)-induced anthocyanin synthesis was determined in the mustard seedling. The curve gives the amount of anthocyanin (A) synthesized within 24 h as a function of the amount of Pfr * produced by a brief light pulse. The [Pfr ] response curve is composed of two linear parts with very different slopes ( a 1,2 ) connected by a relatively narrow transient range (curved segment). The [Pfr ] response curve extrapolates precisely through zero [Pfr ]. The reciprocity law is valid over the whole range investigated (up to 320 s of irradiation). It is concluded that the initial (or primary) reaction of Pfr (Pfr + X → Pfr X) does not involve any significant cooperativity in the case of phytochrome-mediated anthocyanin synthesis. It is speculated that the linear parts of the [Pfr ] response curve truly reflect the mode of phytochrome action ( A = a 1,2 [Pfr ]; X does not come into play since it is not rate limiting) whereas the curved segment represents a transition of the reaction matrix of Pfr . The large difference between a1 and a2 seems to indicate that the physiological effectiveness of a given amount of Pfr (or Pfr X) is determined by [Pfr ] through a Pfr -induced change in the reaction matrix. 相似文献
13.
Abstract— The sequence of primary events following light absorption by light adapted bacteriorhodopsin (bR570 ) is considered by analyzing recent picosecond absorption and emission data. The analysis is facilitated by theoretical calculations which allow us to characterize the properties of the first excited singlet state. It is concluded that excitation leads to the eventual population of a photochemically important nonfluorescent excited state (I) which decays into a photoproduct (J625 )- In J625 , which is most probably a ground state molecule, the chromophore has undergone a structural change, presumably trans → 13- cis isomerization. It is suggested that the subsequent process
reflects a relaxation of the protein environment involving proton transfer. 相似文献
reflects a relaxation of the protein environment involving proton transfer. 相似文献
14.
Abstract— The Kubelka-Munk theory for diffuse reflectance has been applied to a quantitative study of photochromism in the crystalline state. For three systems investigated it was found possible to assign first order rate constants to the thermal relaxation process and estimate the pre-exponential factor A and the activation energy Ea in Arrhenius equation. For the fading of the red photocolored form, Λmax =490 mμ, of benzaldehyde phenylhydrazone A = 1.4×108 min-1 and Ea = 15.7 kcal mole-1 . For the fading of the blue photocolored form, Λmax =590 mμ, of 2–(2,4-dinitrobenzyl)pyridine A= 5×1014 min-1 Ea =23.3 kcal mole-1 , Cinnamaldehyde semicarbazone showing 'reversed phototropy' has a photoactivated state, Λmax =400 mμ, which in dark is transformed into a strongly absorbing yellow species, Λmax = 430 mμ with A = 14 × 1010 min-1 and Ea = 18.7 kcal mole-1 . 相似文献
15.
J. Zechner G. Köhler N. Getoff I. Tatischeff R. Klein 《Photochemistry and photobiology》1981,34(2):163-168
Abstract— The two main primary photoprocesses (electron ejection and H-atom release) for indole, 5-methoxyindole and N-methylindole in various polar and nonpolar solvents were studied as a function of the excitation energy and were correlated with the corresponding fluorescence quantum yields. In hydrocarbon solvents, N–H bond cleavage is the main primary photoprocess from the 1 Bb band of the substrates with the exception of N-methylindole. In alcohols, both processes are of negligible importance. Hydrated electrons (e− aq ) are ejected from the relaxed singlet states of all three compounds in aqueous solutions with a similar yield for excitation at 280 and 254 nm (1 La and 1 Lb states). The yield increases when the excitation is into the 1 Bb band. The quantum yields of the two primary processes from the higher excited states are generally lower than the fraction of molecules not converting to the fluorescent state. This is explained by an efficient back reaction in competition with a thermally activated radical release from an intermediate state or radical pair formed from the S2 (1 Bb ) state. The non-occurrence of a photoionization energy threshold is discussed. 相似文献
16.
SINGLET OXYGEN FORMATION BY SENSITIZATION OF FUROCOUMARINS COMPLEXED WITH, OR BOUND COVALENTLY TO DNA 总被引:1,自引:0,他引:1
N. J. de Mol G. M. J. Beijersbergen van Henegouwen B. van Beele 《Photochemistry and photobiology》1981,34(6):661-666
Abstract— The formation of singlet molecular oxygen (1 O2 ) by sensitization of the furocoumarins 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) and psoralen complexed with DNA was investigated. From the results it is concluded that 5-MOP complexed with native DNA is able to generate 1 O2 , even in a larger extent than 5-MOP free in solution. Also, with 8-MOP and especially with psoralen, 1 O2 formation by the complexed compound could be observed. The 1 O2 formation sensitized by covalently bound furocoumarin was demonstrated with psoralen as a model compound. 4',5'-Dihydropsoralen, a model compound for the UVA light absorbing 4',5'monoadducts of furocoumarins to DNA, is also able to generate 1 O2 . 相似文献
17.
Ravindra L. Arudi Benon H. J. Bielski Augustine O. Allen 《Photochemistry and photobiology》1984,39(5):703-706
Abstract— During the reaction HO2 + HO2 (or O2 - ) = H2 O2 + O2 in aqueous solution, no luminescence in the region 620–720 nm, expected if the product O2 were formed in a singlet state, could be detected. If any singlet O2 is formed, its yield must be less than 10%. Faint luminescence, sometimes found at shorter wavelengths, was shown to arise from reaction of HO2 with impurities in the reagents present. 相似文献
18.
Kotaro T. Yamamoto William O. Smith Jr ‡ Masaki Furuya‡ 《Photochemistry and photobiology》1980,32(2):233-239
The aggregation of phytochrome purified from etiolated pea ( Pisum satirum cv. Alaska) and rye ( Secale cereale cv. Cougar) tissues was investigated by centrifugation and turbidimetry. Purified pea phytochrome (A669 /A280 = 0.88), if irradiated with red light, became precipitable in the presence of CaCl2 . The precipitation upon red-light irradiation was optimal at a Ca2- or Mg2+ concentration of 10–20 m M , was greater at increased phytochrome concentration or lower pH values, and was inhibited by 0.1 M KG. The precipitated phytochrome slowly became soluble after far-red light exposure.
Turbidity of pea phytochrome solutions after red-light irradiation also increased rapidly in the presence of either Ca2+ or Mg2+ . Far-red light exposure after the red light cancelled the turbidity increase. Rye phytochrome showed less turbidity increase than pea phytochrome and occurred only in the presence of Ca2+ . Partially degraded pea phytochrome produced by endogenous proteases in the extract did not show the turbidity increase. Undegraded pea phytochrome also associated with microsomal fractions under conditions similar to those described above, but the partially degraded phytochrome did not. 相似文献
Turbidity of pea phytochrome solutions after red-light irradiation also increased rapidly in the presence of either Ca
19.
Abstract— A very efficient quenching of singlet oxygen (1 O2 ) by N3 - ions has been applied to the determination of rate constants of reactions of 1 O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3 - and A for 1 O2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N3 - . Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N3 - , the 1 O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined. 相似文献
20.
Mannam Krishnamurthy Ashok K. Mishra Sneh K. Dogra 《Photochemistry and photobiology》1987,45(3):359-364
Abstract— The absorption and fluorescence spectra of indole-4-carboxylic acid in various solvents have indicated that the -COOH group is more planar with respect to the indole ring in the first excited singlet state (S1 ) than in the ground (S0 ) state. Relatively large Stokes' shifts indicate that polarisability and dipole moment of the molecule are increased predominantly upon excitation. Prototropic reactions in the S0 and S1 states are the same. The -COO- and -COOH+2 groups are not coplanar in the S0 , but coplanar in the S1 state. pH-dependent fluorescence spectra have revealed that both protonation and deprotonation of the -COOH group increase the basicity of the molecule upon excitation. 相似文献