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Govindjee

Publications and source records attributed to Govindjee.

At least 19 recordsLinked to original sources
PubMed2006

Celebrating 20 years of historical papers in Photosynthesis Research.

This editorial has four goals: (1) to inform the readers of 'Photosynthesis Research' about the past of the 'Historical corner'; which began 20 years ago; (2) to encourage photosynthesis researchers and historians of science to contact me for publishing papers of historical interest; these include: (a) Obituaries and Tributes; (b) historical papers on current and past discoveries and controversies; (c) history of research in specific laboratories, or in specific countries, or at specific conferences; (d) Personal perspectives (not discussed any further); (3) to encourage researchers not to discard, but to save correspondence and data of their discoveries for the future historians by donating them to their Archives, when appropriate (not discussed any further); and (4) to reinforce to the readers that the concept of two-light reaction and two-pigment system was already there in 1959. I mention here three key papers presented at the IXth International Botanical Congress, held at Montreal Canada (in August, 1959) prior to the famous April 9, 1960 paper by Robert Hill and Fay Bendall on the 'Z-scheme' of photosynthesis, that was based on thermodynamic and energetic considerations.

History, 20th Century↗
PubMed2005

Chlorophyll a fluorescence induction kinetics in leaves predicted from a model describing each discrete step of excitation energy and electron transfer associated with Photosystem II.

Chlorophyll a fluorescence induction (FI) is widely used as a probe for studying photosynthesis. On illumination, fluorescence emission rises from an initial level O to a maximum P through transient steps, termed J and I. FI kinetics reflect the overall performance of photosystem II (PSII). Although FI kinetics are commonly and easily measured, there is a lack of consensus as to what controls the characteristic series of transients, partially because most of the current models of FI focus on subsets of reactions of PSII, but not the whole. Here we present a model of fluorescence induction, which includes all discrete energy and electron transfer steps in and around PSII, avoiding any assumptions about what is critical to obtaining O J I P kinetics. This model successfully simulates the observed kinetics of fluorescence induction including O J I P transients. The fluorescence emission in this model was calculated directly from the amount of excited singlet-state chlorophyll in the core and peripheral antennae of PSII. Electron and energy transfer were simulated by a series of linked differential equations. A variable step numerical integration procedure (ode15s) from MATLAB provided a computationally efficient method of solving these linked equations. This in silico representation of the complete molecular system provides an experimental workbench for testing hypotheses as to the underlying mechanism controlling the O J I P kinetics and fluorescence emission at these points. Simulations based on this model showed that J corresponds to the peak concentrations of Q(-)AQB (QA and QB are the first and second quinone electron acceptor of PSII respectively) and Q(-)AQ(-)B and I to the first shoulder in the increase in concentration of Q(-)AQ(2-)B. The P peak coincides with maximum concentrations of both Q(-)AQ(2-)B and PQH2. In addition, simulations using this model suggest that different ratios of the peripheral antenna and core antenna lead to differences in fluorescence emission at O without affecting fluorescence emission at J, I and P. An increase in the concentration of QB-nonreducing PSII centers leads to higher fluorescence emission at O and correspondingly decreases the variable to maximum fluorescence ratio (F v/F m).

Chlorophyll↗
PubMed2004

Discoveries in oxygenic photosynthesis (1727-2003): a perspective.

We present historic discoveries and important observations, related to oxygenic photosynthesis, from 1727 to 2003. The decision to include certain discoveries while omitting others has been difficult. We are aware that ours is an incomplete timeline. In part, this is because the function of this list is to complement, not duplicate, the listing of discoveries in the other papers in these history issues of Photosynthesis Research. In addition, no one can know everything that is in the extensive literature in the field. Furthermore, any judgement about significance presupposes a point of view. This history begins with the observation of the English clergyman Stephen Hales (1677-1761) that plants derive nourishment from the air; it includes the definitive experiments in the 1960-1965 period establishing the two-photosystem and two-light reaction scheme of oxygenic photosynthesis; and includes the near-atomic resolution of the structures of the reaction centers of these two Photosystems, I and II, obtained in 2001-2002 by a team in Berlin, Germany, coordinated by Horst Witt and Wolfgang Saenger. Readers are directed to historical papers in Govindjee and Gest [(2002a) Photosynth Res 73: 1-308], in Govindjee, J. Thomas Beatty and Howard Gest [(2003a) Photosynth Res 76: 1-462], and to other papers in this issue for a more complete picture. Several photographs are provided here. Their selection is based partly on their availability to the authors (see Figures 1-15). Readers may view other photographs in Part 1 (Volume 73, Photosynth Res, 2002), Part 2 (Volume 76, Photosynth Res, 2003) and Part 3 (Volume 80 Photosynth Res, 2004) of the history issues of Photosynthesis Research. Photographs of most of the Nobel-laureates are included in Govindjee, Thomas Beatty and John Allen, this issue. For a complementary time line of anoxygenic photosynthesis, see H. Gest and R. Blankenship (this issue).

Journal Article↗
PubMed2004

Celebrating the millennium: historical highlights of photosynthesis research, part 3.

This paper introduces the third and final part of the 'millennium celebrations of historical highlights of photosynthesis research.' Part 1 (308 pages) was published in October 2002 as Vol. 73 of the journal Photosynthesis Research, and Part 2 (458 pages) was published in July 2003 as Vol. 76. Here, we recognize particularly the work of three major contributors to our understanding of photosynthesis: Roger Stanier (1916-1982); Germaine Cohen-Bazire (Stanier) (1920-2001); and William Arnold (1904-2001). We also introduce the historical papers contained in this volume; consider the legacy of Alfred Nobel (1833-1896); and identify Nobel prizes of special relevance to understanding the capture, conversion, and storage of light energy in both anoxygenic and oxygenic photosynthesis.

Journal Article↗
PubMed2004

A list of photosynthesis conferences and of edited books in photosynthesis.

This paper is a general appendix to the three parts of 'Celebrating the millennium - historical highlights of photosynthesis research' (Photosynthesis Research, Vols~73(2002), 76(2003), 80(2004)). The major part of this paper includes a comprehensive list of most of the edited volumes on research in the area of photosynthesis. However, I begin this paper by describing selected conferences, related to photosynthesis, held in USA, during 1935-1965, followed by the 1963 International Colloquim held in Gif-sur-Yvette, France (René Wurmser (1890-1993), President); and the 2nd Western European Congress (1965), held in the Netherlands, under the leadership of Jan B. Thomas (1907-1991), both these European conferences being the precursors of the first International Congress on Photosynthesis (1968), organized by Helmut Metzner (1925-1999) at Freudenstadt, Germany. A list of the subsequent international photosynthesis congresses is available in Govindjee and David Krogmann (this issue).

Journal Article↗
PubMed2003

Negative feedback regulation is responsible for the non-linear modulation of photosynthetic activity in plants and cyanobacteria exposed to a dynamic light environment.

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I approximately const.+sin(omegat), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance omega and several upper harmonic components (2omega, 3omega and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation, suggesting a regulation limited to PSII. Strong upper harmonic modes were also found in the kinetics of the non-photochemical quenching (NPQ) of chlorophyll fluorescence, of the P700 redox state and of the CO(2) assimilation in tobacco (Nicotiana tabaccum) exposed to harmonically modulated light. They are ascribed to negative feedback regulation of the reactions of the Calvin-Benson cycle limiting the photosynthetic electron transport. We propose that the observed non-linear response of photosynthesis may also be relevant in a natural light environment that is modulated, e.g., by ocean waves, moving canopy or by varying cloud cover. Under controlled laboratory conditions, the non-linear photosynthetic response provides a new insight into dynamics of the regulatory processes.

Adaptation, Physiological↗
PubMed2003

Celebrating the millennium - historical highlights of photosynthesis research, Part 2.

This paper is an introduction to Part 2 of our celebrations of the historical highlights of photosynthesis research. Part 1 was published in October 2002 as Volume 73 of Photosynthesis Research. After a brief introduction, we recognize two giants in the field: Cornelis B. van Niel (for anoxygenic photosynthesis), and Robert Hill (for oxygenic photosynthesis). This is followed by recognition of a 1960 book by Hans Gaffron, and a multi-authored book edited by W. Ruhland and André Pirson, and inclusion in the appendix of a list of selected books. Our celebration is enhanced by the inclusion of beautiful paintings of cells by Antoinette Ryter. After introducing all the historical papers contained in this volume, we honor Louis N. M. Duysens, one of the greatest biophysicists of our time, and finally we dedicate this volume to a great scientist, humanist and peacemaker: Eugene I. Rabinowitch. [12pt] 'Annihilating all that is made To a green thought in a green shade' - Andrew Marvell (1621-1678), The Garden (1681).

Journal Article↗
PubMed2002

A list of personal perspectives with selected quotations, along with lists of tributes, historical notes, Nobel and Kettering awards related to photosynthesis.

The history of photosynthesis research can be found in original papers and books. However, a special history is available from the prefatory chapters and the personal perspectives of various researchers who published them in several journals over the last 40 years. We have compiled a list of such perspectives published since 1964. Selection is not easy, especially of authors who were not directly engaged in photosynthesis research; some are included for their special insights related to central issues in the study of photosynthesis. Our journal, Photosynthesis Research, contains other valuable historic data in the occasional tributes, obituaries and historical notes, that have been published. Lists of these items are included. This article ends by listing the Nobel prizes related to photosynthesis and the Kettering Awards for Excellence in Photosynthesis Research. Wherever possible, a web page address is provided. The web page addresses have been taken from the article 'Photosynthesis and the Web: 2001' by Larry Orr and Govindjee, available at http://www.life.uiuc.edu/govindjee/photoweb and at http://photoscience.la.asu.edu/photosyn/ photoweb/default.html.When I find a bit of leisureI trifle with my papers.This is one of the lesserfrailities.'- Horace, Satires I, IV.

Journal Article↗
PubMed2001

The polyphosphate bodies of Chlamydomonas reinhardtii possess a proton-pumping pyrophosphatase and are similar to acidocalcisomes.

Acidocalcisomes are acidic calcium storage compartments described initially in trypanosomatid and apicomplexan parasites. In this work, we describe organelles with properties similar to acidocalcisomes in the green alga Chlamydomonas reinhardtii. Nigericin and NH(4)Cl released (45)Ca(2+) from preloaded permeabilized cells, suggesting the incorporation of a significant amount of this cation into an acidic compartment. X-ray microanalysis of the electron-dense vacuoles or polyphosphate bodies of C. reinhardtii showed large amounts of phosphorus, magnesium, calcium, and zinc. Immunofluorescence microscopy, using antisera raised against a peptide sequence of the vacuolar type proton pyrophosphatase (H(+)-PPase) of Arabidopsis thaliana which is conserved in the C. reinhardtii enzyme, indicated localization in the plasma membrane, in intracellular vacuoles, and the contractile vacuole where it colocalized with the vacuolar proton ATPase (V-H(+)-ATPase). Purification of the electron-dense vacuoles using iodixanol density gradients indicated a preferential localization of the H(+)-PPase and the V-H(+)-ATPase activities in addition to high concentrations of PP(i) and short and long chain polyphosphate, but lack of markers for mitochondria and chloroplasts. In isolated electron-dense vacuoles, PP(i)-driven proton translocation was stimulated by potassium ions and inhibited by the PP(i) analog aminomethylenediphosphonate. Potassium fluoride, imidodiphosphate, N,N'-dicyclohexylcarbodiimide, and N-ethylmaleimide also inhibited PP(i) hydrolysis in the isolated organelles in a dose-dependent manner. These results indicate that the electron-dense vacuoles of C. reinhardtii are very similar to acidocalcisomes with regard to their chemical composition and the presence of proton pumps. Polyphosphate was also localized to the contractile vacuole by 4',6-diamidino-2-phenylindole staining, suggesting, with the immunochemical data, a link between these organelles and the acidocalcisomes.

Acids↗
PubMed2001

Photosynthesis and the web: 2001.

First, a brief history of the Internet and the World Wide Web is presented. This is followed by relevant information on photosynthesis-related web sites grouped into several categories: (1) large group sites, (2) comprehensive overview sites, (3) specific subject sites, (4) individual researcher sites, (5) kindergarten through high school (K-12) educational sites, (6) books and journals, and, 7) other useful sites. A section on searching the Web is also included. Finally, we have included an appendix with all of the web sites discussed herein as well as other web sites that space did not allow. Readers are requested to send comments, corrections and additions to gov@uiuc.edu.

Journal Article↗
PubMed2000

Global spectral-kinetic analysis of room temperature chlorophyll a fluorescence from light-harvesting antenna mutants of barley.

This study presents a novel measurement, and simulation, of the time-resolved room temperature chlorophyll a fluorescence emission spectra from leaves of the barley wild-type and chlorophyll-b-deficient chlorina (clo) f2 and f104 mutants. The primary data were collected with a streak-camera-based picosecond-pulsed fluorometer that simultaneously records the spectral distribution and time dependence of the fluorescence decay. A new global spectral-kinetic analysis programme method, termed the double convolution integral (DCI) method, was developed to convolve the exciting laser pulse shape with a multimodal-distributed decay profile function that is again convolved with the spectral emission band amplitude functions. We report several key results obtained by the simultaneous spectral-kinetic acquisition and DCI methods. First, under conditions of dark-level fluorescence, when photosystem II (PS II) photochemistry is at a maximum at room temperature, both the clo f2 and clo f104 mutants exhibit very similar PS II spectral-decay contours as the wild-type (wt), with the main band centred around 685 nm. Second, dark-level fluorescence is strongly influenced beyond 700 nm by broad emission bands from PS I, and its associated antennae proteins, which exhibit much more rapid decay kinetics and strong integrated amplitudes. In particular a 705-720 nm band is present in all three samples, with a 710 nm band predominating in the clo f2 leaves. When the PS II photochemistry becomes inhibited, maximizing the fluorescence yield, both the clo f104 mutant and the wt exhibit lifetime increases for their major distribution modes from the minimal 205-500 ps range to the maximal 1500-2500 ps range for both the 685 nm and 740 nm bands. The clo f2 mutant, however, exhibits several unique spectral-kinetic properties, attributed to its unique PS I antennae and thylakoid structure, indicating changes in both PS II fluorescence reabsorption and PS II to PS I energy transfer pathways compared to the wt and clo f104. Photoprotective energy dissipation mediated by the xanthophyll cycle pigments and the PsbS protein was uninhibited in the clo f104 mutant but, as commonly reported in the literature, significantly inhibited in the clo f2; the inhibited energy dissipation is partly attributed to its thylakoid structure and PS II to PS I energy transfer properties. It is concluded that it is imperative with steady-state fluorometers, especially for in vivo studies of PS II efficiency or photoprotective energy dissipation, to quantify the influence of the PS I spectral emission.

Chlorophyll↗
PubMed2000

Greening of intermittent-light-grown bean plants in continuous light: thylakoid components in relation to photosynthetic performance and capacity for photoprotection.

Phaseolus vulgaris (cvv. Windsor longpod and snap bean) plants, etiolated during germination, were exposed to intermittent light (2 min light every 2 hr) for up to 68 hr and then transferred to continuous white light. On transfer of the plants to continuous light (100 photons mumol m-2 s-1, 24 degrees C), the quantum yield of oxygen evolution increased two-fold in about 30 hr. The chlorophyll content per unit leaf area or unit fresh weight increased dramatically, but the fresh weight per unit leaf area was relatively constant. The changes were expressed on the basis of fresh weight or leaf area. On this basis, the contents of photosystem (PS) I and II increased in continuous light, by a factor of 3 and 8, respectively. While the chlorophyll b content and the contents of apoproteins of light-harvesting chlorophyll-protein complexes (LHCIIb, CP29, CP26 and CP24) increased markedly, neither the total carotenoid content nor the de-epoxidation state of the xanthophylls [ratio of zeaxanthin(Z) + antheraxanthin(A) to (Z + A + violaxanthin) was about 0.4)] responded significantly on transfer to continuous light. The fast rise of the flash-induced electrochromic signal (delta A518) was well correlated with the increases in PS I and PS II reaction centres, and with chlorophyll b and total carotenoid contents. The increase in the quantum yield of oxygen evolution during greening in continuous light is attributed to a more balanced distribution of excitation energy between the two photosystems, facilitated by the increased number of PS II units, the increased antenna size of each unit and the enhancement of grana formation. The chloroplast in intermittent light was found to contain abundant xanthophyll cycle pigments and the psbS gene product, presumably adequate for photoprotection in continuous light as soon as chlorophyll a/b- protein complexes are synthesized. The results suggest that greening in continuous light is accompanied by adjustments that include enhanced quantum efficiency of photosynthesis and development of a capacity for harmless dissipation of excess excitation energy.

Fabaceae↗
PubMed1998

Inorganic anions induce state changes in spinach thylakoid membranes.

The role of cations in excitation energy distribution between the two photosystems of photosynthesis is well established. This paper provides evidence, for the first time, for an important role of anions in the regulation of distribution of absorbed light energy between the two photosystems. Inorganic anions caused redistribution of energy more in favour of photosystem I, as judged from measurements of chlorophyll a fluorescence transients, rates of electron transport in low light and 77 K fluorescence emission spectra: the Fv/Fm ratio was decreased by inorganic anions even in the presence of DCMU, the PS II electron transport was decreased whereas PS I electron transport was increased and the F735 (77 K emission from PS I)/F685 (77 K emission from PS II) ratio was increased. Such changes were observed with inorganic anions having different valencies (Cl- , SO4(2-), PO4(3-)): the higher the valency of the inorganic anion, the more the energy transferred towards PS I. Change in the valency of the inorganic anions thus regulates distribution of absorbed light energy between the two photosystems. However, organic anions like acetate, succinate, and citrate caused no significant changes in the Fv/Fm ratio, and in rates of PS I and PS II electron transport, showing their ineffectiveness in regulating light energy distribution.

Anions↗
PubMed1998

Loss of inhibition by formate in newly constructed photosystem II D1 mutants, D1-R257E and D1-R257M, of Chlamydomonas reinhardtii.

Formate is known to cause significant inhibition in the electron and proton transfers in photosystem II (PSII); this inhibition is uniquely reversed by bicarbonate. It has been suggested that bicarbonate functions by providing ligands to the non-heme iron and by facilitating protonation of the secondary plastoquinone QB. Numerous lines of evidence indicate an intimate relationship of bicarbonate and formate binding of PSII. To investigate the potential amino acid binding environment of bicarbonate/formate in the QB niche, arginine 257 of the PSII D1 polypeptide in the unicellular green alga Chlamydomonas reinhardtii was mutated into a glutamate (D1-R257E) and a methionine (DQ-R257M). The two mutants share the following characteristics. (1) Both have a drastically reduced sensitivity to formate. (2) A larger fraction of QA- persists after flash illumination, which indicates an altered equilibrium constant of the reaction QA-QB<-->QA QB-, in the direction of [QA-], or a larger fraction of non-QB centers. However, there appears to be no significant difference in the rate of electron transfer from QA- to QB. (3) The overall rate of oxygen evolution is significantly reduced, most likely due to changes in the equilibrium constant on the electron acceptor side of PSII or due to a larger fraction in non-QB centers. Additional effects on the donor side cannot yet be excluded. (4) The binding affinity for the herbicide DCMU is unaltered. (5) The mutants grow photosynthetically, but at a decreased (approximately 70% of the wild type) level. (6) The Fo level was elevated (approximately 40-50%) which could be due to a decrease in the excitation energy transfer from the antenna to the PSII reaction center, and/or to an increased level of [QA-] in the dark. (7) A decreased (approximately 10%) ratio of F685 (mainly from CP43) and F695 (mainly from CP47) to F715 (mainly from PSI) emission bands at 77 K suggests a change in the antenna complex. Taken together these results lead to the conclusion that D1-R257 with the positively charged side chain is important for the fully normal functioning of PSII and of growth, and is specially critical for the in vivo binding of formate. Several alternatives are discussed to explain the almost normal functioning of the D1-R257E and D1-R257M mutants.

Animals↗
PubMed1997

Modification of the photosystem II acceptor side function in a D1 mutant (arginine-269-glycine) of Chlamydomonas reinhardti.

Bicarbonate anions have a strong positive influence on the electron and proton transfers in photosystem II (PS II). It has been suggested that bicarbonate binds to the non-heme iron and the QB binding niche of the PS II reaction center. To investigate the potential amino acid binding environment of bicarbonate, an arginine residue (R269) of the D1 protein of PS II of Chlamydomonas reinhardtii was mutated into a glycine; our characterization of the resultant mutant (D1-R269G) shows that both the TyrD+ and QA- Fe2+ EPR signals are substantially reduced and assembly of the tetranuclear Mn is lost (R.S. Hutchison, J. Xiong, R.T. Sayre, Govindjee, Biochim. Biophys. Acta 1277 (1996) 83-92). In order to understand the molecular implications of this mutation on the electron acceptor side of PS II, we used chlorophyll (Chl) a fluorescence as a probe of PS II structure and function, and herbicide binding as a probe for changes in the QB binding niche of PS II. Chl fluorescence measurements with the heterotrophically grown D1-R269G mutant cells (or thylakoids), as compared to that of the wild type, show that: rate of electron transfer from QA to the plastoquinone pool, measured by flash-induced Chl a fluorescence decay kinetics, is reduced by - 17 fold; the minimum Chl a fluorescence yield when all QA- is oxidized, is elevated by 2 fold; the level of stable charge separation as inferred from variable Chl fluorescence is reduced by 44%; binary oscillation pattern of variable Chl a fluorescence obtained after a series of light flashes is absent, indicative of the loss of functioning of the two-electron gate on the PS II acceptor side; 77 K PS II Chl a fluorescence emission bands (F685 and F695) are reduced by 20-30% (assuming no change in the PS I emission band). Thermoluminescence data with thylakoids show the absence of the S2QA- and S2QB- bands in the mutant. Herbicide 14C-terbutryn binding measurements, also with thylakoids, show that the QB niche of the mutant is significantly modified, at least 7-8 fold increased terbutryn dissociation constant is shown (220 nM in the mutant versus 29 nM in the wild type); the PS II sensitivity to bicarbonate-reversible formate inhibition is reduced by 5 fold in the mutant, although the formate/bicarbonate binding site still exists in the mutant. This suggests that D1-R269 must play some role in the binding niche of bicarbonate. On the basis of the above observations, we conclude that the D1-R269G mutation has not only altered the structure and function of PS II (QB niche being abnormal), but may also have a decreased net excitation energy transfer from the PS II core to the reaction center and/or an increased number of inactivated reaction center II. We also discuss a possible scenario for these effects using a recently constructed three dimensional model of the PS II reaction center.

Animals↗
PubMed1997

Mutagenesis of the D-E loop of photosystem II reaction centre protein D1. Function and assembly of photosystem II.

The sequence connecting alpha-helices D and E of the D1 protein in photosystem II (PSII) is longer than that found in the corresponding loop of the L subunit in the rhodobacterial reaction centre. This sequence was mutated in order to determine its role in oxygenic photosynthesis. Site-specific mutants, including point mutations and deletions of different size, of the PEST-like region and the putative cleavage area in the D-E loop of the D protein were constructed in Synechocystis sp. PCC 6803. The effects of mutations on the functional and structural properties of PSII and turnover of the D1 protein were examined. Our results demonstrate that deletion of either the PEST-like sequence (deltaR225-F239) or the putative cleavage region (deltaG240-V249, deltaR225-V249) of the D1 protein resulted in severe perturbations on the function of the QB electron acceptor of PSII. However, PSII centres of the mutant with deleted PEST region remained functional enough to support autotrophic growth whereas deletions of the putative cleavage region prevented autotrophic growth. Although enhanced degradation rates of the mutant D1 proteins under low-light growth conditions demonstrate that neither the PEST-like sequence nor the putative cleavage region are required for D1 proteolysis, it became clear that the extension in the D-E loop of the D1 protein is essential for proper PSII assembly and photoautotrophic growth. Moreover, modifications of the D-E loop resulted in transcriptional activation of the psbA gene, indicating that neither light intensity, as such, nor the activity of the electron transfer chain are the only determinants in regulation of psbA gene transcription.

Amino Acid Sequence↗
PubMed1997

Comparison of Different Effects of Chloroacetates on Electron Transports in PS II and in the Reaction Center of Rb. sphaeroides 601.

Chloroacetates displayed different effects on electron transports in the photosynthetic reaction center of purple bacteria (Rb.sphaeroides 601) and in the photosystem II (PS II) of higher plants. Decays of chlorophyII a fluorescence measured after actinic flashes show that chloroacetates inhibit the electron transport from Q(A)(-) to Q(B) (Q(B)(-)) and the equilibrium between Q(A)(-)Q(B) (Q(B)(-)) and Q(A)Q(B)(-) (Q(B)(2-)), acting on electron transport as well as proton transduction. The study on PSII electron transport indicates another inhibition site of chloroacetate at the oxidation side of PSII. Chloroacetates up to 500 mM have no inhibition on the DCPIPH(2) right curved arrow MV electron transport in the RS601's chromatophores. Dissociation constants of OP and trichloroacetates from RS601 reaction center were assessed to be 1.1x10(-3) M and from Dixon curve respectively. The differences on aspects of structures and functions between RS601 reaction center and PS II were discussed.

Journal Article↗