Green Plant Photosynthesis Research Articles

Spectral properties of chlorophyll a monolayers in the presence of an exogenous electron donor and acceptor.

Chlorophyll a monolayers are studied at a nitrogen-water interface in the presence of a reducing or oxidizing agent: sodium ascorbate and benzyl viologen, respectively. Absorption spectra of the films are measured directly on the aqueous surface. With the aid of a computer, fourth derivative and difference spectra are determined. In the presence of ascorbate, a bathochromic shift of the absorption maximum to 693 nm can be induced as compared to 683 nm for a chlorophyll monolayer without any additives. In the presence of ascorbate, chlorophyll species at 676, 712 and 750 nm (present in a pure chlorophyll monolayer) are decreased or diminished. Illumination causes no change in the position of these absorption maxima; however, there is an increase of the absorbance of the main red absorption band. In the presence of benzyl viologen there is a hypsochromic shift of the red absorption maximum to 679 nm. Chlorophyll species at 670, 694, 712 and 740 nm (present in pure chlorophyll monolayers) are decreased or diminished upon addition of benzyl viologen. Upon illumination, there is a decrease in absorbance at 686 nm. It appears that the redox reagents induce the formation of specific chlorophyll aggregates, in the interfacial system, which might be analogous to the various chlorophyll species observed in green plant photosynthesis.

The relationship of CO 2 assimilation pathways and photorespiration to the physiological quantum requirement of green plant photosynthesis

The quantum requirement of green cells for CO 2 fixation has been evaluated and discussed in view of the recent discovery of photorespiration and of multiple biochemical pathways for photosynthetic CO 2 fixation. The reported quantum requirement of algae generally is near 9 quanta per CO 2 fixed. It is suggested that the high CO 2 concentrations and low O 2 concentrations used for these algae experiments would have completely suppressed photorespiration and, therefore, the minimum number of quanta required to fix 1 CO 2 molecule was correctly determined in these experiments. With higher plant leaves, when measurements are made under physiological environments, quantum requirements range from about 12 to 20 quanta per CO 2 fixed. It is suggested that these physiological quantum requirements are higher because photorespiration is functional in these leaves and that photorespiration requires energy. The energy requirement of photorespiration was derived using biochemical models of leaf photosynthesis combining photorespiration with specific biochemical pathways for CO 2 fixation. The calculated physiological quantum requirements for C 3, C 4 and CAM plant photosynthesis are 13, 15 and 17 respectively. The literature values on quantum requirements correspond well with these biochemical models of net photosynthesis. However, it was concluded that the biochemical models fail to give a complete description of photosynthesis in plants using the C 4-dicarboxylic acid cycle.

Green plant photosynthesis. Upconversion or not?

Green plant photosynthesis. Upconversion or not?

Tripartite model for the photochemical apparatus of green plant photosynthesis.

Equations for fluorescence and the rates of photochemistry of photosystem I and photosystem II are derived from a photochemical model for the photosynthetic apparatus that includes the various interactions of the light-harvesting chlorophyll a/b complex with photosystem I and photosystem II as specific photochemical rate constants. The degree of coupling between photosystem II and the chlorophyll a/b complex which is expressed as a product of two probability terms plays a central role in this three-pigment system. The cycling of excitation energy back and forth between photosystem II and the chlorophyll a/b complex increases the exciton density in both arrays of chlorophyll according to a simple analytical expression in the equations. These equations of the tripartite model provide new and credible insights into the photochemical apparatus of photosynthesis.

Inhibition of spinach-leaf phosphofructokinase by 2-phosphoglycollate

A considerable amount of the CO? fixed during photosynthesis in green plants is utilised for the synthesis of starch in chloroplasts. The possibility that the subsequent degradation of this starch might involve formation of triose phosphates which can be easily exported to the cytoplasm [ 1 J was recently strengthened by the detection, in this laboratory, of phosphofructokinase activity in chloroplasts [2] . Experiments described in this communication have confirmed that phosphoglycollate, a proposed intermediate of photorespiration, inhibits the activity of spinach-leaf phosphofructokinase. Strong inhibition of the chloroplast enzyme may significantly hinder the degradation of chloroplast starch during daylight hours.

Experimental examination of the “energy upconversion” theory for green plant photosynthesis

Spinach chloroplasts, dark adapted for periods of three days to three months, yield P700(+) formation (electron spin resonance signal 1) on the first as well as the following flashes in an actinic series of xenon light flashes of 10 mus duration. These data are in contradiction with the prediction of the "energy upconversion" theory [F. K. Fong (1975) Appl. Phys. 6, 151-156] that only the second flash would be effective.

Electron spin resonance spectrum of species “X” which may function as the primary electron acceptor in Photosystem I of green plant photosynthesis

Purified Photosystem I particles from spinach when reduced with 10 mM dithionite at pH 9 exhibited a 50% light reversible-ESR Signal 1 ( P-700 +) at about 10 K. It was possible to show by signal-averaging techniques that a light-reversible ESR spectrum concomitant with the reversible Signal 1 can be observed with approximate principal g factors at g = 2.07, g = 1.86 and g = 1.75.

Protein-Protein interactions of light-harvesting pigment protein from spinach chloroplasts. I. Ca 2+ binding and its relation to protein association

The role of divalent cations in the regulation of the distribution of excitation energy between the two photosystems involved in green plant photosynthesis has led us to search for a better understanding of how such phenomena might occur at the molecular level. Since small changes in orientation of and distance between pigment molecules could greatly affect the distribution of excitation energy, we have decided to study the effects of ions on the light-harvesting pigment protein from spinach chloroplasts. The light-harvesting pigment protein is shown to have two types of binding sites for Ca 2+. Binding studies and analytical ultracentrifugation indicate that site I ( K d = 2.5 μM, n = 1.5−4.0 μmol Ca 2+ bound/mg chlorophyll) is lost as the protein associates. Site II ( K d = 32 μM, n = 9.5 μmol Ca 2+/mg chlorophyll) is not affected by the association of the protein. This site is responsible, however, for a further divalent cation-dependent association of the protein. The possible role of this protein in grana stacking and control of spillover is discussed.

The electric generator in the photosynthesis of green plants. II. Kinetic correlation between protolytic reactions and redox reactions

In a preceding paper (Junge, W. and Ausländer, W. (1974) Biochim. Biophys. Acta 333, 59–70), we attributed the four protolytic reactions at the outer and the inner side of the functional membrane of photosynthesis to the protolytic properties of the redox components, water, plastoquinone and the terminal acceptor. The experimental evidence presented was conclusive except for one argument. The rate of the protolytic reactions as detected by the dye cresol red after a short flash of light was considerably slower than the rate of the corresponding redox reactions. In this communication it is demonstrated that the rate of proton uptake from the outer phase of the functional membrane is slowed down by a diffusion barrier for protons which shields the redox reaction sites at the outer side of the membrane against the outer aqueous phase. This barrier can be lowered by sand grinding the chloroplasts, by digitonin treatment and by uncoupling agents. At the extreme the barrier can be practically eliminated to yield rates of proton uptake matching the rates of the corresponding redox reactions. This gives conclusive evidence that the electrochemical potential difference which light induces across the functional membrane of photosynthesis is generated by a vectorial electron-hydrogen transport system as postulated by Mitchell (e.g. (1966) Biol. Rev. 41, 445–502).

Flash photolysis — electron spin resonance studies of the dynamics of photosystem I: III temperature dependence of the decay of signal I

Summary Using the technique of flash photolysis — electron spin resonance (FPESR), we have confirmed that a portion of the ESR Signal I (P700) of Photosystem I in green-plant photosynthesis responds reversibly to light at low temperatures. In the temperature range 150K to 270K the decay of Signal I follows a normal first-order Arrhenius behavior with an activation energy of 5.5 ± 0.5 kcal mole −1 . Below ∼150K most of the light-induced signal is “frozen in”; however, 10–30% of the Signal responds reversibly to light and exhibits a decay halflife of ∼0.8s. This halflife is temperature independent from 5K to 150K. This phenomenon is interpreted in terms of a quantum-mechanical tunnelling model for the reverse electron transfer in the reaction center of Photosystem I.

Photoselection studies on the orientation of chlorophyll aI in the functional membrane of photosynthesis

The orientation of chlorophyll a I in the functional membrane of photosynthesis in green plants is studied by a photoselection technique. On excitation of an isotropic suspension of isolated spinach chloroplasts with a linearly polarized flash of light linear dichroism of the absorption changes of chlorophyll a I (wavelengths 705 and 430 nm) is observed. The dichroism is maximum for excitation at wavelengths greater than 690 nm, medium at excitation into the blue band of the chloroplast absorption spectrum, and it is small if excitation goes into all red transition moments above 600 nm. This reflects the degree of order between the transition moments of the antennae system around Photosystem I. We conclude as to a higher order between the transition moments at the long-wavelength end of the spectrum in comparison with a lower degree of order between the transition moments belonging to the intervall from 600 to 680 nm. This confirms the results of other authors which were obtained with oriented chloroplasts. However, the photoselection approach avoids characteristic artifacts which may affect linear-dichroism studies with oriented membranes. A quantitative interpretation of the observed photoinduced dichroism of chlorophyll a I to yield the orientation of the respective porphyrin rings in the membrane is not feasible yet due to the absence of specific information on the symmetry properties of the antennae system and on the geometry of the chlorophyll a I aggregate. Under the assumption of a circular degenerate antennae system a rather flat inclination of chlorophyll a I has to be expected.

A kinetic model of the primary back reaction in photosynthesis of green plants

A model is proposed to explain the nonexponential decay kinetics of the primary back reaction of photosystem II and of delayed light in green plants. This model assumes that the primary back reaction is due to the recombination of the primary oxidized photoproduct Z + and the primary reduced photoproduct Q − which are embedded in a fixed position in the reaction center. The formation of a singlet exciton in the bulk chlorophyll molecules as a reaction intermediate is assumed possible. The basic assumption made in this model is that Q − and Z + can cause changes in its surrounding environment to such an extent that it can affect the structure of its neighboring centers. Using this model, the rate of the primary back reaction was calculated and was found to agree well with the experimental kinetic data of Bennoun (1970) . Also, theoretical curves of the kinetics of delayed light in the seconds region, of thermoluminescene and of chemiluminescence were calculated and were also found to agree well with experimental data. Glow curves and the fluorescence versus excitation light intensity curve were also discussed as further means of studying the primary back reaction.

The electric generator in photosynthesis of green plants. I. Vectorial and protolytic properties of the electron transport chain

Light induces the generation of an electrochemical potential difference across the functional membrane of photosynthesis of green plants. Experimental results on the electrochemical phenomena have been largely interpreted in terms of a vectorial alternating electron hydrogen transport system as originally hypothesized by Mitchell. We asked whether or not the reaction coordinate of the electron transport crosses the membrane, and whether or not the protolytic reactions at either side of the membrane can be understood from the protolytic properties of the redox components involved. For this we studied the flash-light-induced protolytic reactions in the outer and the inner aqueous phase of the chloroplast inner disk membranes. Four sites of protolytic reactions were identified, two at either side of the membrane. One of these sites had to be attributed to the reduction of the terminal electron acceptor at the outer side of the membrane. Evidence is presented for the coupling of the other sites to the oxidation of water at the inner side of the membrane, to the reduction of plastoquinone at the outer side and its oxidation at the inner side, respectively. These results support Mitchell's hypothesis for the generation of an electrochemical potential difference by a vectorial electron transport system.

Monovalent cation-induced inhibition of chlorophyll a fluorescence: Antagonism by divalent cations

Salts of monovalent cations at concentrations less than 10 m m and buffers such as tricine were found to increase spillover from Photosystem II to Photosystem I in green plant photosynthesis as measured by a decrease in chlorophyll a fluorescence at room temperature. At 77 °K, they increased the fluorescence emission at 735 nm relative to the bands at 685 and 693 nm indicating that Photosystem I was receiving a greater part of the excitation energy. Divalent cations and monovalent cations at concentrations greater than 10 m m reversed the fluorescence changes.

On the orientation of chlorophyll- aI in the functional membrane of photosynthesis

Light induced redox reactions in photosystem I in photosynthesis of green plants are indicated by absorp tion changes with maxima at 430 nm and 705 nm. These negative going absorption changes have been attributed to the rapid photooxidation of a special chlorophyll namedP 700 [l] or chlorophyll-u1 [2] . The extremely rapid oxidation of this pigment [3] contributes to the extremely rapid generation of an electric potential difference across the functional membrane of photosynthesis [4-61. Thus the reaction path of the oxidation is likely to be vectorial in the membrane. We studied the orientation of the porphyrin ring of chlorophyll-a1 in the membrane, hoping for a better understanding of the structural conditions of the electric potential generation. Several models for the location and the orientation of this pigment have been discussed in the literature, However, it is obvious that they could not be substantiated by the present resolving power of electron microscopy and X-ray scattering for photosynthetic membranes. Moreover, model studies on the orientation of chlorophylls in bimolecular lipid membranes [7, 8 J cannot be used for conclusions by analogy as to the orientation of chlorophyll-a*, which is distinguished from the bulk chlorophylls by its reactivity and its spectroscopic properties. In principle it should be possible to obtain the desired information from studies on the linear dichroism of this pigment in membranes which are oriented with respect to the lab system. Various attempts to orient the submicroscopic inner membranes of chloroplasts have been reported. The most recent ones were based

Simultaneous quantitative comparison of the optical changes at 700 nm (p700) and electron spin resonance signals in system I of green plant photosynthesis.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSimultaneous quantitative comparison of the optical changes at 700 nm (P700) and electron spin resonance signals in system I of green plant photosynthesisJoseph T. Warden and James R. BoltonCite this: J. Am. Chem. Soc. 1973, 95, 19, 6435–6436Publication Date (Print):September 1, 1973Publication History Published online1 May 2002Published inissue 1 September 1973https://doi.org/10.1021/ja00800a046RIGHTS & PERMISSIONSArticle Views25Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (270 KB) Get e-Alerts Get e-Alerts

The presence of P700 in chloroplast fragments prepared by short time incubation with Triton X-100

A procedure was recently described by R. Malkin ( Biochim. Biophys. Acta, 253 (1971) 421) by which fragments having Photosystem II activity could be derived from chloroplasts. These fragments could photoreduce NADP + but were completely devoid of P700, thus giving considerable support to the new “Three-Light-Reaction” scheme in green plant photosynthesis. The results presented here show that the Triton chloroplast fragments still contain approximately 30 to 40% initial P700 as assayed by EPR and difference spectroscopy. The failure to detect P700 in the earlier publication, either by chemical or photochemical assay, was because of the lack of plastocyanin in the reaction medium. This electron carrier is necessary for the reduction of P700 by ascorbate in the Triton fragments. The photoreduction of methyl viologen or NADP + by these fragments with ascorbate as electron donor in the presence of plastocyanin is shown to be a Photosystem I reaction. The maximal Photosystem I activity is about 35% of that of the starting material. The fragments exhibit an increased EPR Signal II.

Quantum Accumulation in Photosynthetic Oxygen Evolution

Three independent methods have been used to determine the size of the quantum accumulation unit in green plant photosynthesis. This unit is defined as that group of pigment molecules within which quantal absorption acts must take place leading to the evolution of a single O(2) molecule. All three methods take advantage of the nonlinearity of oxygen yield with light dose at very low dosages. The experimental values of this unit size, based on an assumed model for the charge cooperation in O(2) evolution, ranging from 800 to 1600, suggest that there is either limited energy transfer between energy-trapping units or chemical cooperation among oxygen precursors formed in several neighboring energy-trapping units. Widely diffusible essential precursors to molecular oxygen are ruled out by these results. Inhibition studies show that O(2) evolution is blocked when 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) is added to chloroplasts after two preliminary flashes and before a third flash which would have yielded O(2) in the absence of DCMU. This experiment is interpreted as evidence that the site of DCMU inhibition is on the oxidizing side of system II. Pretreatment of chloroplasts with large concentrations of Tris, previously believed to destroy O(2) evolution by blocking an essential reaction in the electron chain between water and system II, may be alternately interpreted as promoting the dark reversal of the system II light-induced electron transfer.

Simultaneous optical and electron spin resonance detection of the primary photoproduct P700 in green plant photosynthesis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSimultaneous optical and electron spin resonance detection of the primary photoproduct P700 in green plant photosynthesisJoseph T. Warden and James R. BoltonCite this: J. Am. Chem. Soc. 1972, 94, 12, 4351–4353Publication Date (Print):June 1, 1972Publication History Published online1 May 2002Published inissue 1 June 1972https://doi.org/10.1021/ja00767a058RIGHTS & PERMISSIONSArticle Views37Altmetric-Citations40LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (368 KB) Get e-Alerts Get e-Alerts

Analysis of photosystem II using particle II preparation<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>. I. Experimental evidence supporting the idea of the involvement of two light reactions in photosystem II of green plant photosynthesis

Analysis of photosystem II using particle II preparation<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>. I. Experimental evidence supporting the idea of the involvement of two light reactions in photosystem II of green plant photosynthesis