Search

A supramolecular triad constructed via axially coordinating imidazole-appended fulleropyrrolidine was shown to be successful model of the photosynthetic antenna-reaction center complex. Efficient energy transfer successfully mimics the combined antenna-reaction center in the natural photosynthesis process.

Research has been conducted on the molecules with the head of precise spacer, shape and label moieties. The synthesis and characterization of these molecules are described.

Research has been conducted on the cyclic electron flow around photosystem I. The hypothesis that the defect in this cyclic electron flow should lead to insufficient (Delta)pH generation has been tested and the results are included.

Research shows that in photosynthetic reaction centers of purple bacteria, conformational changes limit the electron transfer from the reduced primary quinone to the secondary quinone. Further, the electron transfer is not affected by shortening the secondary quinone tail from 50 to 5 carbons but it slows when the quinone position is shifted.

Analysis of the ground-state electronic structures of the 'special pair' bacteriochlorophyll dimer reveals three bacteriochlorophyll species with comparable chemical shifts and one bacteriochlorophyll exhibiting a different shift. Data indicate that the structural changes of the special pair do not impact reorganization energy associated with the charge-transfer process.

Research shows that the properties of P700 are modulated by the hydrogen bond to the 13(sup)1-keto group of chlorophyll a', suggesting that the polarity of the binding pocket influence P700. Furthermore, the oxidation potential of chlorophyll a' is enhanced if the keto group is hydrogen bonded to Thr A739 residue.

Natural neutralization of acidic mining lakes is usually limited by the availability of organic carbon. We investigated whether benthic photosynthesis could contribute to primary production in an acidic mining lake (pH 2.6). The occurrence and light dependence of benthic photosynthesis in the lake was investigated using oxygen microelectrodes. Oxygen microprofiles measured in light and darkness were significantly different, indicating photosynthetic activity. The photic zone was 300 [micro]m thick and the highest photosynthetic activity was found at the sediment surface, which was covered by a dense layer of diatoms. These algae, predominantly Eunotia spp. and Pinnularia obscura, were found to be adapted to low light intensities. The community compensation irradiance was 6.8 [micro]E [m.sup.-2] [s.sup.-1] corresponding to an annual mean compensation depth of 1.8 m, These results imply that 13% of the lake area could have a net efflux of oxygen from the sediment. Even at an irradiance as low as 1.2 [micro]E [m.sup.-2] [s.sup.-1] photosynthetic activity was detected. The relatively low light requirements for benthic photosynthesis in this acidic environment may be due to an efficient absorption of red light, the dominant wavelength available in this ferric iron-rich lake. Our results suggest that benthic photosynthesis can play an important role in the biogeochemistry of acidic mining lakes.

Diatoms are an important functional group of marine phytoplankton because of their role in the fixation of atmospheric carbon dioxide (C[O.sub.2] and transfer of organic carbon to deep waters. Carbon-concentrating-mechanisms, such as active C[O.sub.2] and bicarbonate (HC[O.sup.-.sub.3]) uptake and carbonic anhydrase activity, are believed to be essential to marine photosynthesis, because the main carbon-fixing enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase, is less than half saturated at normal seawater C[O.sub.2] concentrations. On the basis of short-term inorganic [sup.14]C uptake experiments, Tortell et al. (1997; Nature 390: 243-244) recently argued that marine diatoms are capable of HC[O.sup.-sub.3] uptake. However, as discussed herein, the extent of HC[O.sup.-.sub.3] uptake cannot be assessed on the basis of these experiments. Using short-term [sup.14]C[O.sub.2]-disequilibrium experiments, we show that a clone of the marine diatom Phaeodactylum tricornutum takes up little or no HC[O.sup.-.sub.3] even under conditions of severe C[O.sub.2] limitation. Predicting the response of the oceans to increased C[O.sub.2] concentrations will require, among other things, a careful assessment of the extent to which marine algae take up HC[O.sup.-.sub.3] or C[O.sub.2]. Because the plasmalemma of microalgae is gas permeable, all phytoplankton exchange C[O.sub.2] with the growth medium. Experimental results that are merely consistent with HC[O.sup.-.sub.3] uptake are insufficient to prove that HC[O.sup.-.sub.3] uptake is occurring. Our results are in accord with predictions based on stable carbon isotopic fractionation data. Combining isotopic disequilibrium experiments with continuous growth cultures and stable isotope fractionation experiments is a powerful tool for understanding the response of oceanic primary producers to anthropogenic C[O.sub.2] emissions as well as for interpreting paleoceanographic carbon isotope data.

The X-ray absorption fine structure indicates that three di-mu-oxo manganese-manganese motifs may be present in the photosystem II oxygen evolving complex as revealed by the heterogeneity of the S(sub)o state in the 2.7 angstrom manganese-manganese distances.

At least three chlorophyll triplet populations are present in thylakoids that are associated with photosystem II as shown by fluorescence-detected magnetic resonance spectrosopy. The triplets are seen in aerated samples and are formed under nonreducing redox conditions with two generating in the core complex(es) and the other in the external antenna.

Research identifies five unique polypeptides in cyanobacterial photosystem II complex in the HT-3 strain of Synechocystis sp. PCC 6803. The proteins include the SII1638 protein, a homologue of the PsbQ protein, which is present in chloroplast photosystem II complex.

Although there are considerable technical challenges to be overcome during this decade, the prospects for the detection of Earth-like planets (ELPs) orbiting nearby stars are encouraging. If life has developed on some of the ELPs that may be discovered by sophisticated telescope systems, such as the Terrestrial Planet Finder, the detection of photosynthesis is an attractive possibility. Here we discuss the likely preconditions and subsequent events that have led to the occurrence of [O.sub.2]-producing photosynthesis on Earth and then extend this discussion to how this may have occurred on ELPs orbiting in the habitable zone of a variety of main-sequence stars from spectral type F0V to M0V. We point out how the need for liquid water and the need to avoid UV radiation have influenced the evolution of photosynthesis on Earth, how the absorption spectra of the dominant (chlorophyll) photosynthetic pigments may have been determined in natural selection, and how and when the evolution of the ability to use water as an electron donor took place. Models for the photosynthetic productivity of ELPs orbiting at the inner edge of the habitable zone are discussed both from aquatic and land-based photosynthesis, making some allowance for global cloud cover on the ELP. The photosynthetic generation of [O.sub.2] is greatest on cloud-free planets with hot (e.g., F0V) parent stars, though the advantage over cooler stars depends on the fraction of the planet covered by oceans. The low [O.sub.2] generation in ELPs orbiting cooler stars is due to the poor match between the parent star's spectral energy distribution and the assumption of terrestrial pigment properties. We discuss the possibility that a three- or four-photon mechanism might operate on such planets (as opposed to the two-photon system on Earth) and how it could influence the spectral properties of the ELP. We also emphasize the role of tectonic and other geological processes as well as biology in determining the [O.sub.2] level on Earth and on ELPs. Key Words: atmospheres; evolution; Earth; prebiotic environments.

Photosynthetic bacterial reaction centers convert light excitation into chemical free energy. The initial electron transfer leads to the consecutive semireductions of the primary ([Q.sub.A]) and secondary ([Q.sub.B]) quinone acceptors. The [Q.sup.-.sub.A] and [Q.sup.-.sub.B] formations induce proton uptake from the bulk. Their magnitudes ([H.sup.+]/[Q.sup.-.sub.A] and [H.sup.+]/[Q.sup.-.sub.B], respectively) probe the electrostatic interactions within the complex. The pH dependence of [H.sup.+]/[Q.sup.-.sub.A] and [H.sup.+]/[Q.sup.-.sub.B] were studied in five single mutants modified at the L209 site (L209P [right arrow] F,Y,W,E,T). This residue is situated at the border of a continuous chain of water molecules connecting [Q.sub.B] to the bulk. In the wild type (WT), a proton uptake band is present at high pH in the [H.sup.+]/[Q.sup.-.sub.A] and [H.sup.+]/[Q.sup.-.sub.B] curves and is commonly attributed to a cluster of acidic groups situated nearby [Q.sub.B]. In the [H.sup.+]/[Q.sup.-.sub.A] curves of the L209 variants, this band is systematically absent but remains in the [H.sup.+]/[Q.sup.-.sub.B] curves. Moreover, notable increase of [H.sup.+]/[Q.sup.-.sub.B] is observed in the L209 mutants at neutral pH as compared with the WT. The large effects observed in all L209 mutants are not associated with significant structural changes (Kuglstatter, A., Ermler, U., Michel, H., Baciou, L. & Fritzsch, G. Biochemistry (2001) 40, 4253-4260). Our data suggest that, in the L209 mutants, the [Q.sub.B] cluster does not respond to the [Q.sup.-.sub.A] formation as observed in the WT. We propose that, in the mutants, removal of the rigid proline L209 breaks a necessary hydrogen bonding connection between the quinone sites. These findings suggest an important role for structural rigidity in ensuring a functional interaction between quinone binding sites.

Research has been conducted on the meso, meso-linked porphyrin dimer. The incorporation of this dimer as the light-harvesting chromophore into the photosynthetic electron transfer model in constructing ferrocene-meso, meso-linked porphyrin dimer-fullerene triad is reported.

Research has been conducted on the Ca (super)2+ depletion. The structural and functional roles of Ca (super)2+ in the photosynthetic evolution of oxygen have been investigated and are discussed in the article.

Research has been conducted on the S-cycle redox transition of the photosystem II oxygen evolving complex. The pH dependence of this redox transition has been investigated via the electron paramagnetic resonance spectroscopy and the results are reported.

In this study, we used a special measurement geometry with samples placed inside the integrating sphere to address whether significant absorption by aquatic particles exists in the near-infrared (near-IR) spectral region from about 700 to 850 nm. Our tests with inorganic dyes and MgC[O.sub.3] particles showed that placing a small sample (1 cm cuvette) inside a relatively large integrating sphere (15 cm diameter) reduced the scattering error to a negligible level with no adverse effect on the absorption measurement. Our measurements of absorption by various particle suspensions suggest that absorption is generally negligible in the near-IR regardless of the type of particles. We examined four species of phytoplankton, phytodetritus derived from phytoplankton cultures, three samples of natural assemblages of mineral particles that show distinct reddish or brownish color, and three samples of aquatic particles from coastal and inland waters that have varying proportions of organic and inorganic particles., Research into phytoplankton photosynthesis in the near-infrared spectrum between 700 to 850 nm was conducted using inorganic dyes and MgC[O.sub.3] particles. Research results indicate that photosynthesis is generally negligible in the near-infrared spectrum.

Results do not support the temperature dependence theory proposed for the reduction of P680 in photosystem II reactions of photosynthesis. Authors discuss microsecond time scale and nanosecon phase level of proton-coupled electron transfer reactions and the energies these reactions generate to support their claim.

2-Carboxyarabinitol 1-phosphate limits photosynthetic C[O.sub.2] assimilation at low light because it is a potent, naturally occurring inhibitor of ribulose 1,5-bisphosphate carboxylase/oxygenase. Evidence is presented that this inhibitor is derived from chloroplastic fructose 1,6-bisphosphate. First, transgenic plants containing decreased amounts of chloroplastic fructose 1,6-bisphosphate phosphatase contained increased amounts of fructose 1,6-bisphosphate and 2-carboxyarabinitol 1-phosphate and greatly increased amounts of the putative intermediates hamamelose and 2-carboxyarabinitol, which in some cases were as abundant as sucrose. Second, French bean leaves in the light were shown to incorporate [sup.14]C from [sup.14]C[O.sub.2] sequentially into fructose 1,6-bisphosphate, hamamelose bisphosphate, hamamelose monophosphate, hamamelose, and 2-carboxyarabinitol. As shown previously, [sup.14]C assimilated by photosynthesis was also incorporated into 2-carboxyarabinitol 1-phosphate during subsequent darkness.

Results point out that phosphatidylglycerol is indispensable for the structure and function of photosystem reaction center complex and for the structural integrity of the plastoquinone electron acceptor Q(sub)B-binding site. Data show that the lipid deprivation inactivates the electron acceptors in the reaction center.

The S state-dependent chlorophyll fluorescence in the nitric oxide-treated photosystem II exhibits a three-flash downshift, whereas in the electron paramagnetic resonance, the maximum S(sup)-2 signal manifests after the fourth flash. Results suggest that manganese cluster is in a redox state after treatment of photosystem II with nitric oxide.

Results reveal pronounced excitonic interactions between chlorophyll a and b molecules, suggesting that the spectral heterogeneity of a minor photosystem II antenna complex includes contribution of the chlorophyll molecules as well as the contribution from the pigment-protein interactions.

Photosynthetic efficiency of phytoplankton in the Arabian Sea appears to increase during the monsoon period. Nitrate concentrations are elevated and are probably affected by mixed layer depth during this season.

Research has been conducted on the photosynthetic reaction centers. The effect of the identity, energy of the functional substrates and the barriers between the functional substrates on the protein reaction coordinates has been investigated and is described.

Research demonstrates that moderately hydrated photosystem II films in glycerol/water solution, enable measurement of S-state transition difference spectra of the whole water hydroxyl region by Fourier transform infrared spectroscopy. Data indicate that the S-state cycle in these hydrated films is similar to the core samples in solution.

The pigment-protein interactions in the photosystem II antenna protein, Lhcb4, reveal that removal of a any bound cofactor from any sites of the chlorophyll a binding sites, a2, a4, and a5 leads to a loss of bands of the particular chlorophyll molecule and a structural impact on the protein folding.

Research examines the spectral heterogeneity of chlorophylls in the light harvesting complex II of photosynthetic apparatus. Low temperature absorption spectroscopy of a recombinant LHC-II complex reveals that chlorophylls at specific binding sites can be correlated with distinct spectral sub-bands, representing absorption spectra of native and refolded LHC-II complex.

Research has been conducted on the Mn atoms which function as catalysts in the water-oxidizing complex in the PS II oxidizing site. The effect of the PS II proteins' amine groups on the photoligation of the Mn (super)2+ to the apo water-oxidizing complex has been investigated via photoactivation and chemical modification techniques and the results are discussed.

Research has been conducted on the rhenium(I) polypyridine maleimide complexes. The synthesis, photophysical properties and characterization of these complexes have been carried out and the results of the X-ray crystal structure analysis are presented.

We studied relationships between spectral reflectance and photosynthesis of mountain paper birch, Betula papyrifera var. cordifolia (Regel) Fern., leaves from three different elevations on Mt. Mansfield (summit elevation 1339 m above sea level) in the Green Mountains of Vermont, USA. The different reflectance indices we used all suggested progressively increasing stress with increasing elevation. The photochemical reflectance index (PRI) indicated lower photosynthetic radiation use efficiency at higher elevations, the red edge position ([lambda]RE) indicated lower chlorophyll concentrations at higher elevations, and the structure-independent pigment index (SIPI) indicated a higher carotenoid: chlorophyll a ratio at higher elevations. The rate of change in these indices with changes in elevation was much higher than we have observed in our studies of red spruce and balsam fir reflectance along a similar elevational gradient; we take this to be an indicator of the greater susceptibility of paper birch to elevation-related stressors compared to the very stress-tolerant conifers. At all light levels, photosynthesis decreased with increasing elevation; this pattern was most noticeable in the light-saturated rate of photosynthesis ([A.sub.sat]), which was nearly twice as high in low-elevation leaves (17.0 [+ or -] 1.0 [micro]mol*[m.sup.-2]*[s.sup.-1]) than in high-elevation leaves. The quantum yield of photosynthesis ([PHI]) exhibited a similar trend. Furthermore, the highest elevation leaves showed a much sharper transition from the light-limited to the light-saturated part of the light response curve than did the lowest elevation leaves. The photochemical reflectance index was highly correlated with [A.sub.sat] ([r.sup.2] = 0.99) and [PHI] ([r.sup.2] = 0.96). In addition to contributing to our knowledge of the ecophysiology of paper birch along a steep environmental gradient, these results are further evidence of the usefulness of reflectance measures for the rapid and noninvasive detection of plant stress, especially when used in conjunction with direct measurements of photosynthesis. Key words: Betulaceae; Betula papyrifera; elevation; environmental gradient; leaf reflectance; light response curve; mountain paper birch; photosynthesis; stress physiology.

Research has been conducted on the ferredoxin-NADP (super)+ reductase. The distinct forms of this reductase have been expressed in the photosynthetic and nonphotosynthetic plant tissues and the structural and kinetic properties of the nonphotosynthetic isoform examined in defining characteristics related to the tissue-specific function are reported.

Results demonstrate that quenching of chlorophyll fluorescence of the light-harvesting complexes of photosystem II is influenced by protein-protein interactions within thylakoid membranes. The intrasubunit conformational change and intersubunit interactions within the lipid membranes are discussed.

Results demonstrate the presence of 2 beta-carotenes with each arranged in parallel or perpendicular to the membrane plane in the pheophytin modified photosystem II reaction center protein. Data indicate that the 'core' pigments include two Pheo and four Chl, which absorb in the 676-685 nanometer range.

Research has been conducted on the S (sub)3 state of the oxygen-evolving complex in photosystem II. The EPR signal induced by a pH jump to alkaline pH in the S (sub)3 state of this complex has been investigated and the results are discussed.

Research reveals that interrelationships between photosynthesis and respiration in vivo in Synechocystis sp. strain PCC 6803 are evident in terms of differences in succinate levels, the plastoquinone pool redox state, and the NADP reduction state. Data indicate succinate dehydrogenase is the main pathway for electron transfer to plastoquinone pool.

Research demonstrates that the thermodynamic properties of photosystem II core reaction centers of the cyanobacterium Synechocystis sp. PCC 6803 markedly differ from those of bacterial and photosystem I reaction centers.

Research describes interactions between bicarbonate and the Q(sub)B binding site in photosystem II as measured by iron redox-spectra in relation to 0-phenanthroline. Results show that a hydrogen bond network from the non heme iron toward the Q(sub)B pocket involves bicarbonate and histidine D1-215.

Results reveal the dynamic structural changes in the secondary structure of the oxygen evolving complex during successive S-state transitions. Data indicate that the oscillatory pattern of the spectra is due to changes in the amide I and II regions, which reflect the rearrangement of H-bonding partners within photosystem II.

Fourier transform infrared difference spectra show four oscillation patterns for the photosystem II. The flash-induced spectra reveal the individual S-state transitions comprising of symmetric and asymmetric stretching regions of carboxylate groups and amide I region.

Results show that spectral properties and photochemical behavior of xanthophyll pigments are reflections of the individual pigments bound to the light-harvesting complexes. Data on the absorption wavelengths and fluorescence of the bound pigments are discussed.

Results show that illumination at low-temperature generates a mixture of chlorophyll and carotenoid radicals in photosystem II. Data indicate that carotenoid radicals are less stable for recombination while chlorophyll radicals exhibit strong absorption peaks at near-infrared regions. Upon warming the pigments show interconversion between 6 to 120 K.

Results demonstrate that the amino acid changes introduced into the CD-loop region of the photosystem II D2 protein, by combinatorial mutagenesis, result in two charge recombination pathways in photosystem II. Data indicate that the pathways cause changes in the energy gap between redox forms of P680.