ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06168.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Green plants, after illumination, emit light at times far too long to be fluorescence. This delayed light is closely connected with the process of photosynthesis and seems to be one of the few ways of studying the first steps in that process. In this paper we argue that there are at least 3 or maybe 4 mechanisms producing delayed light. (1) The delayed light in the range of 1–100 msec seems to come from the recombination of electrons and holes. The photosynthetic unit must absorb 2 quanta for this process. (2) At longer times the delayed light can come from thermal fluctuations lifting an electron from the level of ferredoxin to that of chlorophyll. The unit need only absorb 1 light quantum for this kind of delayed light. (3) Similarly, a part of the long‐time delayed light comes from the untrapping of holes. (4) A part of the delayed light emitted at times longer than a few minutes seems to involve molecular oxygen. Finally, we shall describe a new phenomenon involving the effect of electric fields on chloroplasts, that we feel will be helpful in understanding the untrapping mechanisms of delayed light produ

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06169.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—How does a plant convert electronic excitation of chlorophyll into stable chemical potential? The time scales of fluorescence (10‐‐9sec) and steady‐state enzymatic turnover (10–2sec) indicate that energy storage must be involved. Millisecond delayed singlet emission from chlorophyll allows measurement of metastable energy storage at Photoreaction II. Activation of noncyclic electron transport results in more rapid decay and in increase of emission at 10‐‐3sec, both effects being inhibited by the poison DCMU. These results can be explained by at least three different models of the reaction center: the oxidized chlorophyll model, the chlorophyll triplet model, and the two‐quantum elec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06170.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Destruction of the oxygen‐evolving activity of chloroplasts by treatment with 0.8MTris‐HC1 results in an extremely rapid dark decay of millisecond delayed light. Addition of electron acceptors such K3Fe(CN)6or NADP+does not change the decay characteristics of this msec delayed light. Artificial electron donors such as DPC partially restore the msec delayed emission to the slowly decaying situation which is found in control chloroplasts. Addition of electron acceptors to this photochemically competent system results in more rapid decay and in an increase of emission at 1 msec, as in control chloroplasts. We suggest on the basis of the delayed light data that Tris treatment induces a rapid side reaction which uselessly dissipates the oxidizing and reducing power which is stored by Photoreaction II. Artificial electron donors allow the Tris‐poisoned photoreaction to store energy long enough for utilization of the energy by normal photosynthetic reactions, as shown by the flattening of the delayed light curves. In the restored system the normal reactions of electron transport are thus able to compete with the Tris‐induced side reaction. This interpretation is supported by the finding that the restored system requires higher exciting intensities for saturation of NADP+reduction than the contr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06171.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—A simple apparatus using a He‐Ne laser and a rotating sector gives repetitive light pulses with rise and fall times of a few μsec and intensities of up to 0.65 W/cm2. Fluorescence during the actinic pulse and luminescence following it (after 20 μsec) may be recorded and compared. Sampling of the suspension of photosynthetic cells or chloroplasts by intermittent flow permits the averaging of 25 such measurements. WithChlorella, the fast (30 μsec) and the medium (30 msec) components of luminescence do not saturate at the same light intensity. The former saturates in the same range as the photochemical fluorescence rise, whereas the latter saturates at higher intensities. Under a variety of conditions, the decay of luminescence intensity is always strongly polyphasic. Analysis of the kinetics discloses a dependency with the log concentration of the hypothetical precursor, suggesting a connection of luminescence with electrochemical phenomena. The shape of the luminescence integral, as well as the light saturation pattern, suggests another kind of interpretation, in terms of several pools, possibly two of equal size. In the presence of hydroxylamine, only one pool is seen. The stimulating effect of preillumination is only observed for the medium component. However, a stimulation of short duration also exists for the fast component. The problems of number of pools, mechanism, and stimulation are briefly dis

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06172.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The behavior of glow curves and of ferricyanide‐induced luminescence in photo‐synthetic bacteria is consistent with a model in which light is emitted when electrons return to oxidized reaction center chlorophyll from the primary acceptor. A number of observations can be explained if it is assumed that the chromatophore membrane potential provides part of the activation energy for the process. The model is tested by inducing light emission by the generation of potassium diffusion potentials in preilluminatedChromatiumchromatop

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06173.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—New results are presented on the emission of oxygen by algae and chloroplasts illuminated by a sequence of short saturating flashes. These results favor the four‐state hypothesis of Kok and co‐workers, in which formation of oxygen requires the accumulation of four oxidants produced by four successive photoreactions. Deactivation of the more oxidized precursor states in the dark is studied under different conditions of preillumination. Our results suggest that both a one step and a two step mechanism of deactivation exist. In order to understand the biological significance of Kok's parameter α—the fraction of photochemical centers unable to react on each flash (“misses”)‐we study reoxidation of acceptorQafter one flash by fluorescence techniques. It appears that a fraction ofQ‐is reoxidized by a back reaction which cancels the effect of the preilluminating flash and is probably responsible for the misses. The results of some luminescence experiments are also reported. These experiments demonstrate that delayed emission of light is associated with the deactivation of states S2andS3. It is possible that excitons produced by deactivation can be reabsorbed by active photochemical centers, which can modify considerably the deac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06174.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—A quantitative analysis is made of a linear 4‐step model for photosynthetic O2evolution in which each photochemical trapping center or an associated enzyme cycles through 5 oxidation states (S0, S1, S2, S3, S4). The overall reaction is:S0→ S4, S4→ S0+ O2, wherekd= rate of dark reaction. Based on data obtained with isolated chloroplasts, four aspects were considered: (1) The two perturbations which damp the oscillation of the O2flash yield in a flash sequence given after a dark period‐(a) a failure rate (α) of the trapping centers in the photochemical conversion (‘misses’) and (b) double effective excitations in a fraction (8) of the centers which are in the S0andS1states (‘double hits’). Best fit with the experimental data is obtained for α= 0.1, β=0.05. (2) The kinetics and the mechanism of deactivation—the loss of + charges (O2precursors) in the dark. The momentary distribution of the four oxidation states (S0‐‐S3) in a sample can be computed from the O2yields of four consecutive flashes with corrections for a and β. The time course of the various states in the dark following specific preilluminations reveals that deactivation proceeds in single equivalent steps: S3→S2, S2,→S1. S1, itself stable in the dark, is the end product of deactivation. The ground stateS0cannot be formed by deactivation in the dark but is only formed during illumination. (3) The various ratios [S0]/[S1] which can be observed in a sample after deactivation following different preilluminations with flashes or continuous light. (4) The transients of the O2evolution rate in weak continuous light as observed after deactivation with or without flash preillumination. In all instances satisfactory agreement is found between the observations a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06175.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Incubating spinach chloroplasts with various chaotropic agents results in inhibition of photosynthetic electron transport between water and Photosystem II similar to the inhibition caused by washing chloroplasts with a high concentration of Tris buffer. Partial restoration of NADP photoreduction and fluorescence of variable yield is achieved by adding hydroquinone or Mn2+, either of which donates electrons to Photosystem II in the inhibited chloroplasts. The inhibitory treatments cause the release of Mn from its bound state in the chloroplast, thus allowing the measurement of the ESR signal of Mn2+. The ESR measurement is used to follow the photooxidation of Mn2+as it donates electrons to photosystem I

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06176.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—The use of sodium dodecyl sulfate to dissociate photosynthetic membranes followed by standard fractionation techniques yields chlorophyll‐proteins and reaction center complexes with molecular weights of 500,000 or less. Much about the structure and function of photo‐synthetic unitsin vivocan be deduced from the properties of the isolated complexes. The Bchl‐protein from green bacteria is approximated by an incompletely filled sphere ˜ 80 Â in diameter consisting of four identical subunits. The five Bchl molecules in each subunit are 14 to 20Â apart. The related Chla‐proteins from a blue‐green alga and various eukaryotic plants may have similar structural characteristics. The Chla‐protein from a blue‐green alga contains one molecule of P700 per 60–90 Chlamolecules. The quantum requirement for P700 oxidation is 2.6 or less. The midpoint potential in various preparations ranges from 0.38 V to 0.42 V. Green algae and higher plants yield a Chla‐protein similar to that from the blue‐green alga; in addition they yield another Chl‐protein (mol. wt. = 2–3×104) which contains an equal amount of Chlaand Chlb. These two Chl‐proteins account for most of the chlorophyll in these organisms. Two photosynthetic bacteria (Rhodopseudomonas viridisandChromatium) yield protein complexes containing Bchl, carotenoid, and bound cytochromes. The reaction center complex fromR. viridiscontains P960 (Em,8=0.39 to 0.42 V), cytochrome 558 (Em,8=0.33 V) and cytochrome 553 (Em,7=—0.02 V). Quantum requirements for P960 and C558 oxidation are ˜2.2 and 3.0, respectively. Complex A fromChromatiumcontains Bchl 890, P883, cytochrome 556 (Em,8= 0.34 V) and cytochrome 552 (Em,7=˜0.04 V). The quantum requirement for C556 oxidation is about 15. Both high‐ and low‐potential cytochromes can donate electrons to the reaction center chlorophyll present in either complex. This fact supports the idea that only one kind of photochemical reaction center functions in photosynthetic bacteria. An hypothesis about the nature of the photosynthe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06177.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY