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51.
The initial (F0), maximal (FM) and steady-state (FS) levels of chlorophyll fluorescence emitted by intact pea leaves exposed to various light intensities and environmental conditions, were measured with a modulated fluorescence technique and were analysed in the context of a theory for the energy fluxes within the photochemical apparatus of photosynthesis. The theoretically derived expressions of the fluorescence signals contain only three terms, X=J2p2F/(1–G), Y=T/(1–G) and V, where V is the relative variable fluorescence, J2 is the light absorption flux in PS II, p2F is the probability of fluorescence from PS II, G and T are, respectively, the probabilities for energy transfer between PS II units and for energy cycling between the reaction center and the chlorophyll pool: F0=X, FM=X/(1–Y) and FS=X(1+(YV/(1–Y))). It is demonstrated that the amplitudes of the previously defined coefficients of chlorophyll fluorescence quenching, qP and qN, reflect, not just photochemical (qP) or nonphotochemical (qN) events as implied in the definitions, but both photochemical and nonphotochemical processes of PS II deactivation. The coefficient qP is a measure of the ratio between the actual macroscopic quantum yield of photochemistry in PS II (41-1) in a given light state and its maximal value measured when all PS II traps are open (41-2) in that state, with 41-3 and 41-4. When the partial connection between PS II units is taken into consideration, 1-qP is nonlinearily related to the fraction of closed reaction centers and is dependent on the rate constants of all (photochemical as well as nonphotochemical) exciton-consuming processes in PS II. On the other hand, 1-qN equals the (normalized) ratio of the rate constant of photochemistry (k2b) to the combined rate constant (kN) of all the nonphotochemical deactivation processes excluding the rate constant k22 of energy transfer between PS II units. It is demonstrated that additional (qualitative) information on the individual rate constants, kN-k22 and k2b, is provided by the fluorescence ratios 1/FM and (1/F0)–(1/FM), respectively. Although, in theory, 41-5 is determined by the value of both k2b and kN-k22, experimental results presented in this paper show that, under various environmental conditions, 41-6 is modulated largely through changes in k
N, confirming the idea that PS II quantum efficiency is dynamically regulated in vivo by nonphotochemical energy dissipation.Abbreviations Chl
chlorophyll
- F0, FM and FS
initial, maximal and steady-state levels of modulated Chl fluorescence emitted by light-adapted leaves
- PS I and II
photosystem I and II
- qP and qN
(previously defined) photochemical and nonphotochemical components of Chl fluorescence quenching 相似文献
52.
We present here an improvement to the analysis of oxygen evolution with four sigma coefficients (4-S) by computing z, the sum of the S-state probabilities, which was introduced earlier (Delrieu and Rosengard 1987, Biochim Biophys Acta 892: 163–171). We demonstrate that z is equal to the ratio of two consecutive Mean Y (the estimation of the steady state oxygen production based on local properties) found by three sigma analysis. The quantity z is useful for computing double-hits, and for showing the inactivation/activation processes of PS II complexes. Three sigma analysis assumes z=1 exactly; since this is not verified, it is argued that four sigma analysis is closer to the real workings of the water oxidizing complex. Oxygen evolution can then be interpreted in the frame of a modified Kok's model where the sum of the probabilities equals z. We therefore suggest that the closer fitting of four sigma analysis to oxygen production data is not simply due to an extra, unnecessary variable, but to the fact that PS II complexes can be inactivated and reactivated under flashing light. Finally, in order to facilitate the use of four sigma analysis, a computer program is made available upon request. 相似文献
53.
A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS II and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, FVFM, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and FVFM ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.Abbreviations FM
maximum total fluorescence
- F0
initial fluorescence
- FV
maximum variable fluorescence
- PS
Photosystem
- QA, QB
primary and secondary electron acceptors of Photosystem II 相似文献
54.
Summary Irradiation of the principal photosystem II light-harvesting chlorophyll-protein antenna complex, LHC II, with high light intensities brings about a pronounced quenching of the chlorophyll fluorescence. Illumination of isolated thylakoids with high light intensities generates the formation of quenching centres within LHC II in vivo, as demonstrated by fluorescence excitation spectroscopy. In the isolated complex it is demonstrated that the light-induced fluorescence quenching: a) shows a partial, biphasic reversibility in the dark; b) is approximately proportional to the light intensity; c) is almost independent of temperature in the range 0–30°C; d) is substantially insensitive to protein modifying reagents and treatments; e) occurs in the absence of oxygen. A possible physiological importance of the phenomenon is discussed in terms of a mechanism capable of dissipating excess excitation energy within the photosystem II antenna.Abbreviations chla
chlorophyll a
- chlb
chlorophyll b
- F0
fluorescence yield with reaction centers open
- Fm
fluorescence yield with reaction centres closed
- Fi
fluorescence at the plateau level of the fast induction phase
- LHC II
light-harvesting chlorophyll a/b protein complex II
- PS II
photosystem II
- PSI
photosystem I
- Tricine
N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine 相似文献
55.
Varda Mann Ilana Ekstein Hilde Nissen Carrie Hiser Lee Mclntosh Joseph Hirschberg 《Plant molecular biology》1991,17(3):559-566
We have cloned and analyzed the sugar-beet mitochondrial gene for cytochrome oxidase subunit II (coxII). The sugar-beet and its deduced amino acid sequence were compared to its homologouscoxII gene sequences from both monocot and dicot plants. It was found to be highly conserved (89–95%) compared to homologue in other plant species. The 780 bp coding sequence of the sugar beetcoxII gene is interrupted at position 383 by a 1463 bp intron. This intron contains an additional 107 bp sequence that is not found in any of the plantcoxII genes studied thus far. The structure of the intron suggests that a large intron existed in an ancestralcoxII gene before monocots and dicots diverged in evolution. Three CGG codons in the sugar-beetcoxII coding sequence align with conserved tryptophan residues in the homologous gene of other species, suggesting that RNA editing takes place also in sugar-beet mitochondria. In 13 out of 24 codons ofcoxII mRNA that were found to be edited in four other plants, the sugar-beet gene already utilizes the edited codons. This phenomenon may indicate that the mitochondrial genome in sugar-beet is phylogenetically more archaic relative to these plants. An additional sequence of 279 bp that is identical to the first exon ofcoxII was identified in the mtDNA of the sugar-beet. This pseudo-gene is transcribed and its existence in the mitochondrial genome is unexplained. 相似文献
56.
Y. Umebachi 《Amino acids》1992,2(1-2):181-187
Summary Papiliochrome II is a pale yellow pigment of butterflies and consists of one molecule each ofL-kynurenine and N--alanyldopamine (NBAD). The aromatic amino nitrogen of kynurenine is bonded to the-carbon of NBAD. There are isomers IIa and IIb which show opposite circular dichroism. The-alanine contents of IIa and IIb were determined and the molar ratio of IIa to IIb has proved to be 1.17. The IIa and IIb were decomposed toL-kynurenine and N--alanylnorepinephrine (NBANE) by being heated in water at 80°C for 30 min. In both IIa and IIb, circular dichroism of the NBANE showed the same positive peak at 280 nm. The NBANE were further decomposed to-alanine and norepinephrine (NE) by being heated in 1 N HC1 at 100°C for 2 hr. The NE was submitted to enantioseparation and has proved to be a racemic mixture in both cases of IIa and IIb. These results are discussed in the light of the enzymic synthesis of IIa and IIb. 相似文献
57.
A phosphorylated analogue of DSIP at Ser7 has been shown to exist endogenously by immunochemical studies. An enzyme which could phosphorylate DSIP has not yet been identified. In the present study, we examined DSIP as a substrate for in vitro phosphorylation by casein kinase II. DSIP was phosphorylated by the enzyme with apparent Km and Vmax values of 20 mM and 90.9 nmol/min/mg protein, respectively. Both ATP and GTP were utilized as phosphoryl donors. Phosphorylation of DSIP was inhibited by heparin and enhanced by spermine. These results demonstrate that DSIP can serve as a possible substrate for casein kinase II in vitro. 相似文献
58.
Production and characterization of alloantisera specific for bovine class II major histocompatibility complex antigens 总被引:1,自引:0,他引:1
Ten alloantisera defining five major histocompatibility complex (MHC) class II specificities of the bovine lymphocyte antigen (BoLA) complex were produced and characterized. Eight antisera defining four of the specificities were generated by immunizing cattle with class I compatible-class II incompatible lymphocytes. The alloantiserum defining the fifth class II specificity was produced by skin implant immunization. A pregnancy serum specific for one of the class II specificities was also identified. The class II antigens recognized by these antisera were designated 'Dx' antigens to indicate that they are BoLA-D region antigens encoded by one or more undetermined class II loci. The molecules identified by the alloantisera are heterodimers composed of a 34-kd alpha and a 26- to 28-kd beta chain, and are expressed on B-lymphocytes but not on resting T-lymphocytes. In family studies the BoLA-Dx antigens segregated in linkage with the BoLA-A locus alleles. Most of the BoLA-A alleles present in the Cornell Holstein herd at a high frequency were found to exist in gametic association with two or more serologically defined class II haplotypes. On the basis of a population study it was determined that three pairs of class I and class II alleles (w10-Dx4, w31-Dx5, and c3-Dx2) were present in the Cornell herd at significantly increased frequencies. 相似文献
59.
J. T. Keltjens J. M. H. Hermans G. J. F. A. Rijsdijk C. Van der Drift G. D. Vogels 《Antonie van Leeuwenhoek》1988,54(3):207-220
F430 is the prosthetic group of the methylcoenzyme M reductase of methanogenic bacteria. The compound isolated from Methanosarcina barkeri appears to be identical to the one obtained from the only distinctly related Methanobacterium thermoautotrophicum. F430 is thermolabile and in the presence of acetonitrile or C10
in4
sup-
two epimerization products are obtained upon heating; in the absence of these compounds F430 is oxidized to 12, 13-didehydro-F430. The latter is stereoselectively reduced under H2 atmosphere to F430 by cell-free extracts of M. barkeri or M. thermoautotrophicum. H2 may be replaced by the reduced methanogenic electron carrier coenzyme F420.Abbreviations CH3S-CoM
methylcoenzyme M, 2-methylthioethanesulfonic acid
- HS-CoM
coenzyme M, 2-mercaptoethanesulfonic acid
- F430
Ni(II) tetrahydro-(12, 13)-corphin with a uroporphinoid (III) ligand skeleton
- 13-epi-F430 and 12,13-di-epi-F430
the 12, 13- and 12, 13-derivatives of F430
- 12, 13-didehydro-F430
F430 oxidized at C-12 and C-13
- coenzyme F420
7,8-didemethyl-8-hydroxy-5-deazaflavin derivative
- coenzyme F420H2
reduced coenzyme F420
- MV+
methylviologen semiquinone
- HPLC
high-performance liquid chromatography 相似文献
60.
Absorption changes at 325 nm (delta A325) induced by 15 ps laser flashes (lambda = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (PI QA-) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 x 10(14) photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (delta A closed 325) from those in open RCs (delta A open 325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo- with a time constant of about 350 +/- 100 ps. 相似文献