Little is known of the physiological and biochemical mechanisms underlying competitive interactions between alien invasive grasses and native taxa, and how these are affected by resource supply. Consequently, this study compared photosystem II (PS II) function, photosynthetic gas and water exchange, enzyme and pigment concentrations, flowering and biomass accumulation in an indigenous geophyte, Tritonia crocata (L.) Ker. Gawl., grown in monoculture and admixed with the alien grass, Lolium multiflorum Lam., at different levels of water and nutrient supply. Diminished stomatal conductances were the primary cause of reduced net C02 assimilation rates, and consequent biomass accumulation in T. crocata admixed with L. multiflorum at all levels of water and nutrient supply with one exception. These corresponded with decreased soil water contents induced presumably by more efficient competition for water by L. multiflorum, whose biomass was inversely correlated with soil water content. Biochemical impairments to photosynthesis were also apparent in T. crocata admixed with L. multiflorum at low levels of water and nutrient supply. These included a decline in the density of working photosystems (reaction center per chlorophyll RC/ABS), which corresponded with a decreased leaf chlorophyll a content and a decreased efficiency of conversion of excitation energy to electron transport (¥0 / l-^o), pointing to a reduction in electron transport capacity beyond QA~, a decline in apparent carboxylation efficiency and Rubisco content. At low nutrient levels but high water supply, non-stomatal induced biochemical impairments to photosynthesis (decreased RC/ABS, chlorophyll a and Rubisco content) were apparent in T. crocata admixed with L. multiflorum. These attributed to a reallocation of fixed carbohydrate reserves to floral production which increased significantly in T. crocata under these conditions only and associated with a corresponding reduction in the mass of its underground storage organ (bulb). The results of this study did not support the hypothesis that under conditions of low water and low nutrient supply invasive annual grasses would have a lesser impact on the growth and physiology of native geophytes than under resource enriched conditions that favor growth of these grasses. Unresolved is whether resource limitation and allelopathic mechanisms functioned simultaneously in the inhibition of the native geophyte by the alien grass. / Thesis (M. Environmental Science (Ecological Remediation and Sustainable Utilisation))--North-West University, Potchefstroom Campus, 2008.

Chemnitz, Techn. Univ., Diss., 2007.

Techn. University, Diss., 2003--Berlin.

This qualification work is trying to shed a little bit more light on some proteins present in higher plants, which structure and function in photosynthetic reaction remain unclear. In particular it treats proteins of photosystem II, called PsbR, PsbW and PsbX that are responsible for photosynthetic reaction optimization. This thesis contains data about proteins acquisition and their sequences elucidation.

abstract: Photosystem II (PSII) is a large protein-cofactor complex. The first step in photosynthesis involves the harvesting of light energy from the sun by the antenna (made of pigments) of the PSII trans-membrane complex. The harvested excitation energy is transferred from the antenna complex to the reaction center of the PSII, which leads to a light-driven charge separation event, from water to plastoquinone. This phenomenal process has been producing the oxygen that maintains the oxygenic environment of our planet for the past 2.5 billion years. The oxygen molecule formation involves the light-driven extraction of 4 electrons and protons from two water molecules through a multistep reaction, in which the Oxygen Evolving Center (OEC) of PSII cycles through 5 different oxidation states, S0 to S4. Unraveling the water-splitting mechanism remains as a grant challenge in the field of photosynthesis research. This requires the development of an entirely new capability, the ability to produce molecular movies. This dissertation advances a novel technique, Serial Femtosecond X-ray crystallography (SFX), into a new realm whereby such time-resolved molecular movies may be attained. The ultimate goal is to make a “molecular movie” that reveals the dynamics of the water splitting mechanism using time-resolved SFX (TRSFX) experiments and the uniquely enabling features of X-ray Free-Electron Laser (XFEL) for the study of biological processes. This thesis presents the development of SFX techniques, including development of new methods to analyze millions of diffraction patterns (~100 terabytes of data per XFEL experiment) with the goal of solving the X-ray structures in different transition states. ii The research comprises significant advancements to XFEL software packages (e.g., Cheetah and CrystFEL). Initially these programs could evaluate only 8-10% of all the data acquired successfully. This research demonstrates that with manual optimizations, the evaluation success rate was enhanced to 40-50%. These improvements have enabled TR-SFX, for the first time, to examine the double excited state (S3) of PSII at 5.5-Å. This breakthrough demonstrated the first indication of conformational changes between the ground (S1) and the double-excited (S3) states, a result fully consistent with theoretical predictions. The power of the TR-SFX technique was further demonstrated with proof-of principle experiments on Photoactive Yellow Protein (PYP) micro-crystals that high temporal (10-ns) and spatial (1.5-Å) resolution structures could be achieved. In summary, this dissertation research heralds the development of the TR-SFX technique, protocols, and associated data analysis methods that will usher into practice a new era in structural biology for the recording of ‘molecular movies’ of any biomolecular process. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2015

<p>This thesis deals with the impact of hydrogen bonding on the properties of phenols. The possibility for tyrosine to form hydrogen bonds to other amino acids has been found to be important for its function as an electron transfer mediator in a number of important redox enzymes. This study has focused on modeling the function of tyrosine in Photosystem II, a crucial enzyme in the photosynthetic pathway of green plants.</p><p>Hydrogen bonds between phenol and amines in both inter- and intramolecular systems have been studied with quantum chemical calculations and also in some solid-state structures involving phenol and imidazole.</p><p>Different phenols linked to amines have been synthesized and their possibilities of forming intra- and intermolecular hydrogen bonds have been studied as well as the thermodynamics and kinetics of the generation of phenoxyl radicals via oxidation reactions.</p><p>Since carboxylates may in principle act as hydrogen bond acceptors in a manner similar to imidazole, proton coupled electron transfer has also been studied for a few phenols intramolecularly hydrogen bonded to carboxylates with the aim to elucidate the mechanism for oxidation. Electron transfer in a new linked phenol—ruthenium(II)trisbipyridine complex was studied as well.</p><p>The knowledge is important for the ultimate goal of the project, which is to transform solar energy into a fuel by an artificial mimic of the natural photosynthetic apparatus</p>

The photosynthetic process has the unique ability to capture energy from sunlight and accumulate that energy in sugars and starch. This thesis deals with the light driven part of photosynthesis. The aim has been to investigate how the light-absorbing protein complexes Photosystem I (PS I) and Photosystem II (PS II), react upon illumination of light with lower energy (far-red light; 700-850 nm) than the absorption peak at respective primary donor, P700 and P680.  The results were unexpected. At 295 K, we showed that both PS I and PS II were able to perform photochemistry with light up to 130 nm above its respective primary donor absorption maxima. As such, it was found that the primary donors’ action spectra extended approximately 80 nm further out into the red-region of the spectrum than previously reported.  The ability to perform photochemistry with far-red light was conserved at cryogenic temperatures (&lt; 77 K) in both photosystems. By performing EPR measurements on various photosystem preparations, under different illumination conditions the origin of the effect was localized to their respective reaction center. It is also likely that underlying mechanism is analogous for PS I and PS II, given the similarities in spatial coordination of the reaction center pigments. For PS II, the results obtained allowed us to suggest a model involving a previously unknown electron transfer pathway. This model is based upon the conclusion that the primary cation from primary charge separation induced by far-red light resides primarily on ChlD1 in P680. This is in contrast to the cation being located on PD1, as has been suggested as for visible light illumination. The property to drive photochemistry with far-red wavelengths implies a hither to unknown absorption band, probably originating from the pigments that compose P700 and P680. The results presented here might clarify how the pigments inside P680 are coupled and also how the complex charge separation processes within the first picoseconds that initiate photosynthetic reactions occur.

Photosystem II is a unique enzyme which catalyzes light induced water oxidation. This process is driven by highly oxidizing ensemble of four Chl molecules, PD1, PD2, ChlD1 and ChlD2 called, P680. Excitation of one of the Chls in P680 leads to the primary charge separation, P680+Pheo-. Pheo- transfers electrons sequentially to the primary quinone acceptor QA and the secondary quinone acceptor QB. P680+ in turn extracts electrons from Mn4CaO5 cluster, a site for the water oxidation. There are two redox active tyrosines, TyrZ and TyrD, found in PSII. They are symmetrically located on the D1 and D2 central proteins. Only TyrZ acts as intermediate electron carrier between P680 and Mn4CaO5 cluster, while TyrD does not participate in the linear electron flow and stays oxidized under light conditions. Both tyrosines are involved in PCET. The reduced TyrD undergoes biphasic oxidation with the fast (msec-sec time range) and the slow (tens of seconds time range) kinetic phases. We assign these phases to two populations of PSII centers with proximal or distal water positions. We also suggest that the TyrD oxidation and stability is regulated by the new small lumenal protein subunit, PsbTn. The possible involvement of PsbTn protein in the proton translocation mechanism from TyrD is suggested. To assess the possible localization of primary cation in P680 the formation of the triplet state of P680 and the oxidation of TyrZ and TyrD were followed under visible and far-red light. We proposed that far-red light induces the cation formation on ChlD1. Transmembrane interaction between QB and TyrZ has been studied. The different oxidation yield of TyrZ, measured as a S1 split EPR signal was correlated to the conformational change of protein induced by the QB presence at the QB-site. The change is transferred via H-bonds to the corresponding His-residues via helix D of the D1 protein.

Doctor of Philosophy / Department of Chemistry / Ryszard J. Jankowiak / The constituents of oxygen-evolving photosystem II core complexes—antenna proteins (CP43 and CP47) and reaction center (RC)—have been the subject of many studies over the years. However, the various issues related to electronic structure, including the origin/composition of the lowest-energy traps, origin of various emission bands, excitation energy transfer (EET), primary charge separation (CS) processes and pigment site energies remain yet to be fully resolved. Exploiting our state-of-the-art techniques such as low-T absorption, fluorescence, and hole burning (HB) spectroscopies, we resolved some of the issues particularly related to CP47 and isolated RC protein complexes. For example, we demonstrated that the fluorescence origin band maximum (~695 nm) originates from the lowest-energy state ~693 nm of intact CP47. In intact CP47 in contrast to destablished protein complexes, the band (~695 nm) does not shift in the temperature range of 5–77 K unless hole-burning takes place. We also studied a large number of isolated RC preparations from spinach, and wild-type Chlamydomonas reinhardtii (at different levels of intactness), as well as its mutant (D2-L209H), in which the active branch pheophytin (PheoD1) has been genetically replaced with chlorophyll a (Chl a). We showed that the Qx-/Qy-region site-energies of PheoD1 and PheoD2 are ~545/680 nm and ~541.5/670 nm, respectively, in good agreement with our previous assignment [Jankowiak et al. J. Phys. Chem. B 2002, 106, 8803]. Finally, we demonstrated that the primary electron donor in isolated algal RCs from C. reinhardtii (referred to as RC684) is PD1 and/or PD2 of the special Chl pair (analogous to PL and PM, the special BChl pair of the bacterial RC) and not ChlD1. However, the latter can also be the primary electron donor (minor pathway) in RC684 depending on the realization of the energetic disorder. We further demonstrate that transient HB spectra in RC684 are very similar to P+QA - PQA spectra measured in PSII core, providing the first evidence that RC684 represent intact isolated RC that also possesses the secondary electron acceptor, QA. In summary, a new insight into possible charge separation pathways in isolated PSII RCs has been provided.

The delivery of nutrients to the surface of marine algae can be controlled by the local hydrodynamic regime: in higher flow velocities, the Diffusive Boundary Layer (DBL) at the uptake surface is thinner, which can increase the flux of dissolved chemicals to the algal surface. If the primary productivity of an alga is controlled by the availability of a dissolved chemical, increased water flow should result in greater primary productivity due to increased chemical flux. To test the hypothesis that increased water flow will increase Photosystem II kinematics (PSII) in the green alga Caulerpa we used a Diving Pam Fluorometer to measure the maximum relative electron transport rate (Pmax), Saturation Irradiance (Ik), Non-photochemical quenching (NPQ), the light limited slope of photosynthesis vs. irradiance curve (α) and photo-chemical quenching (qP) and compared these measured values among treatments of varying flow speeds in a portable laboratory flume. We also measured the influence of water flow on values of Pmax, Ik, α , qP and NPQ in the field. Results showed that in C. racemosa collected from Tampa bay, and tested in a laboratory flume, values of Pmax and Ik were positively correlated to increase water flow, possibly indicating mass-transfer limitation. C. mexicana, collected from the Florida Keys, showed a decrease in values of Pmax, and Ik with increasing water velocity in flume experiments, indicating that the increased flow was resulting in physiological stress. This result was supported with field measurements for C. sertularioides, which showed a negative correlation between Pmax and flow velocity and Ik and flow velocity.