Photosystem II (PSII) is the membrane-bound oxidoreductase peptide complex responsible for the oxidation of water to molecular oxygen and reduction of plastoquinone to plastoquinol. Primary electron transfer is initiated upon absorption of a photon by the primary donor chl resulting in electron transfer and production of a P680+QA charge separated state. P680+ is reduced by YZ (Y161 of the D1 polypeptide subunit), one of two redox-active tyrosine residues found in PSII. This produces a neutral tyrosyl radical (YZ ) which is subsequently reduced by electrons derived from water at the oxygen-evolving complex (OEC). The OEC is composed of four manganese, one calcium ion, and one chloride ion. Four photons are required to convert water to O2, each photon advancing the OEC through successive oxidation states or S states. The exact chemical mechanism of water oxidation in PSII is not known. However, proton-coupled electron transfer (PCET) is thought to be one of the fundamental steps in driving the extraction of electrons and protons from water. Here, the mechanism of water oxidation is investigated with focus on PCET events using vibrational spectroscopy. Vibrational spectroscopy is sensitive to changes in protein structure, charge, and hydrogen bonding, and is ideal for the study of fast events coupled with light-induced electron transfer. The results presented here demonstrate the utility of time-resolved infrared spectroscopy in the detection of intermediates of photosynthetic water oxidation. We suggest that proton transfer may precede manganese oxidation during water oxidation based on time-resolved infrared and difference FT-IR spectroscopic results. The mechanism of PCET associated with YZ reduction is investigated. Using reaction-induced difference FT-IR spectroscopy, the identity of the chloride binding site is speculated through the use of bromide exchange at the OEC. Also, proton transfer reactions at the OEC are investigated using azide as a vibrational probe. The advances in the understanding of photosynthetic water oxidation gained in this work will aid in the elucidation of the chemical mechanism of this important reaction. Understanding the details of photosynthetic water oxidation will assist in the development of technology aimed at harnessing the energy of the sun for the benefit of humankind.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nutrition and Food Science, 1976 / Vita. / Includes bibliographies. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Nutrition and Food Science

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The 3-PG physiological/mensurational hybrid model is a useful forest management tool capable of producing accurate growth results across a number of parameterised species. The temperature data used in the model are the average maximum and minimum values for photosynthesis above the compensation point (Landsberg and Sands 2011). There is a minimum temperature below which positive net CO₂ exchange will not occur, a maximum temperature above which it will not occur and an optimum temperature at which it is maximised. These parameters are used in the 3-PG physiological model of forest production. However, a species’ photosynthetic response to short-term variation may differ from one season to another as species acclimate to temperatures over periods of a few weeks. In this study, acclimation responses of four species of eucalypt and Sequoia sempervirens to long-term temperatures were studied over a wide range of short-term temperature changes in order to identify the minimum, optimum and maximum temperatures of CO₂ assimilation for physiological/mensurational hybrid modelling, and also to identify the sites for which the species would be best suited. In order to achieve the aims of this study, a growth chamber experiment was established. Seedlings of four eucalypt species and Sequoia sempervirens were grown at base-line day/night temperatures of 30/16, 22/12 and 10/5ºC in controlled environment chambers for three months and leaf gas exchange measurements were made of the species at seven short-term temperature levels (5, 10, 15, 20, 25, 30 and 35ºC). The optimum and the maximum temperatures for net photosynthesis increased with an increase in base-line temperature for all species. The highest optimum temperature and net photosynthetic rates recorded were in plants grown at 30/16ºC and the lowest were in those grown at 10/5ºC. The maximum rate of net CO₂ assimilation increased with the temperature at which plants were grown partly because of acclimation in key photosynthetic processes in the Calvin cycle. Responses of maximal carboxylation rate (Vcmax) and also the maximal light-driven electron flux (Jmax) to short-term temperature change varied with base-line temperature for all species studied. Net photosynthesis and photosynthetic parameters measured did not vary significantly with effects of nitrogen, phosphorus and their interaction (p = 0.1468). The ratio of Jmax to Vcmax decreased with increasing leaf temperatures for all species (p < 0.001). These results indicate that the species studied will adapt to long-run changes in temperature, and the parameters obtained from these studies can be used for models that simulate the physiology and growth of the species.

Magistrantūros studijų baigiamajame darbe pateikiami žirnių fotosintezės pigmentų, prolino, sacharidų bei santykinės drėgmės pokytis lapuose esant drėgmės deficitui. Tyrimų objektas – `Ilgiai` veislės sėjamasis žirnis (Pisum sativum L.). Darbo metodai. Tyrimai atlikti Aleksandro Stulginskio universiteto Agrobiotechnologijos laboratorijoje 2012-2013 metais. Žirniai pasėti į 0,16 m x 0,23 m (aukštis x diametras) vegetacinius indus su substratu (pH − 6,31, P2O5 − 633,94 mg kg-1, K2O – 912 mg kg-1). Eksperimentas vykdytas 6 pakartojimais po 5 augalus inde. Augalai auginti programuojamoje auginimo kameroje esant 20/18 °C (diena/naktis) temperatūrai, 16/8 val. (diena/naktis) fotoperiodui, 50 µmol m-2 s-1 apšviestumui. Augalai auginti programuojamoje auginimo kameroje aukščiau nurodytomis sąlygomis bei esant drėgmės deficitui substrate. Sausros tyrimas pradėtas po sėjos praėjus trims savaitėms. Darbo rezultatai. Esant drėgmės deficitui, patikimai didžiausi chlorofilo a ir b bei karotenoidų kiekiai žirniuose (atitinkamai 2,501 ir 0,821, bei 1,059 mg l-1) nustatyti praėjus 8 dienoms po laistymo. Esmingai didžiausi prolino ir sacharidų kiekiai (atitinkamai 46,543 μM g-1 ir 0,155 g kg-1) žirniuose, esant drėgmės deficitui, nustatytas praėjus 12-ai dienų. Dirvožemio drėgnis (SWC) esmingai kito visą tyrimų laikotarpį. Mažiausias dirvožemio drėgnis (15,12 proc.) nustatytas paskutinę tyrimų dieną, praėjus 16-ai dienų po paskutinio laistymo. Santykinis vandens kiekis lapuose (RWC) esmingai... [toliau žr. visą tekstą] / Master’s thesis submitted to pea’s photosynthesis pigments, proline, saccharins and relative humidity change in leaves and the influence of humidity. The object of researches – ‘Ilgiai’ variety of sowing peas (Pisum sativum L.) Methods. Research carried out at Aleksandras Stulginskis University in Laboratory of Agrobiotechnology 2012–2013. Peas were sown in 0.16 m x 0.23 m (height x diameter) vegetative vessels with the substratum (pH – 6.31, P2O5 – 633.94 mg kg-1, K2O – 912 mg kg-1). The experiment was carried out in 6 replicates of 5 plants in container. Plants were cultivated at programmable climatic chamber at 20/18 °C (day/night) temperature, 16/8 hours (day/night) photoperiod, 50 µmol m-2 s-1 illumination. Plants were grown at programmable climatic chamber by conditions which are set out above and with deficit of moisture in substrate. The investigation of drought launched after three weeks of sowing. Results. In the moisture deficit, reliably the largest chlorophyll a and b and carotenoids amount in peas (respectively 2.501 and 0.821, and 1.059 mg l-1) were determined after 8 days after watering. Essentially the maximum proline and saccharins contents (by 46.543 μM g-1 and 0.155 g kg1) in peas at the moisture deficit were set after 12 days. Soil water content (SWC) was essentially varying through all period of researches. Minimum soil humidity (15.12 percent) was established at the last day of researches, passing 16 days after last watering. Relative water content in... [to full text]

Photosynthesis is responsible for fixing approximately 111 – 117 Pg of CO₂ into organic carbon each year, of which about half is performed by algae in the oceans. Over geological timescales, photosynthesis by algae was instrumental in transforming Earth’s atmosphere. Despite the integral role algae play in the carbon cycle, the interaction and feedbacks between CO₂ fixation by algae and atmospheric CO₂ is poorly understood. This thesis expands upon our current knowledge by tracing the evolution of the key enzyme of photosynthesis, Rubisco, in algae through geological history. It was found that Rubisco underwent adaptation during distinct periods corresponding with falling atmospheric CO₂. The pattern of adaptation hints at physiological adaptation to varying concentrations of atmospheric CO2 and possibly indicates the emergence of carbon concentrating mechanisms (CCMs). This adaptation was probed further within the red and chromist algae, identifying key residues within the Rubisco protein sequence that may influence its kinetic properties. This research also provided new measurements of Rubisco CO2 affinity within the haptophyte algae. Finally, the importance of HCO₃- use by phytoplankton in the modern ocean was explored. HCO₃- utilisation was modelled through signals retained within stable carbon isotopes of organic matter estimate the response to anthropogenic increases of CO₂. The results indicate that phytoplankton utilise a large proportion HCO₃- which shows little sensitivity to anthropogenic increases of CO₂, even when model predictions are extended to 2100. This thesis demonstrates how algae can respond to CO₂ levels over geological and anthropogenic time scales.

Tropical montane cloud forests (TMCF) are one of the most fascinating, but least understood ecosystems in the world, and the interest in the carbon (C) cycle of TMCFs with regard to carbon sequestration and storage practices has increased rapidly in recent years. One feature that prevails in all TMCFs is a decrease in aboveground net primary productivity (ANPP) and standing biomass and leaf area index (LAI) with increasing altitude, together with the stunted growth form of the trees. This thesis focuses on the input part of the TMCF C-cycle, and investigates the controlling factors on photosynthesis on a leaf, canopy, and ecosystem level in the Kosñipata valley in south east Peru, on the eastern slope of the Andes (13º11’28’’S / 71º35’24’’W). Leaf traits are known to relate to foliar C-exchange, and compared with other altitudinal transect studies of TMCFs, the studied sites had similar altitudinal trends for foliar nitrogen (N) content (though not for phosphorus) and leaf mass per area (LMA), with N content decreasing and LMA increasing with altitude. N concentrations were relatively high and LMA values relatively low, but this observed relationship was consistent with those found in global leaf trait surveys. Examining plant stoichiometry (i.e. N:P ratios), the data suggests that unlike the general hypothesis, the Kosñipata forests are not N limited, except for the study site at 2990 m a.s.l. At the 2990 m a.s.l. site, which is the focal study site of the thesis, photosynthetic parameters Vcmax (the carboxylation efficiency of the Rubisco protein) and Jmax (the electron transport efficiency) proved to be similar to those found in lowland tropical rainforest leaves when expressed on an area basis and standardised to 25 °C (55.6 ± 2.6 and 106.5 ± 5.2 mmol m-2 s-1, for Vcmax and Jmax, respectively). However, when standardised to the mean ambient TMCF temperature of 12.5 °C, both photosynthetic parameters were much lower than ambient tropical rainforest Vcmax and Jmax values. The TMCF Jmax -Vcmax relationships were steeper than found in other tropical biomes, indicating a possible adaptation to the lower light availability in TMCFs because of frequent cloud cover, or a consequence of little atmospheric evaporative demand, which is also due to the humid conditions in this forest type. Although N-Vcmax relationships were significant (P<0.05), the fit was not very strong and the relationship between nitrogen use efficiency (NUE) and Vcmax indicates that TMCF species can be regarded as a different plant functional type compared with other tropical forest types. Diurnal measurements of net photosynthesis (A), stomatal conductance (gs) and leaf water potential (Yleaf) showed that different TMCF species experienced non-contrasting diurnal patterns of Yleaf and gs in the dry season. The observed patterns suggest that some TMCF species can be classified as isohydric species, while others behave anisohydrically. Additionally, in situ gs was not very responsive to these to the range of experienced photosynthetically active radiation (PAR), vapour pressure deficit (VPD) or soil water content (SWC), leading to the conclusion that in the studied TMCF, drought stress does not play a role in C-uptake. When using the measured photosynthetic parameters for up-scaling C-uptake to stand scale with a Soil-Plant-Atmosphere model, simulated annual gross primary productivity (GPP) was 16.24 ±1.6 T C ha-1 yr-1, which is about half the GPP observed in neotropical lowland rainforests. Analyses of the modelled results showed that GPP in this TMCF is mostly controlled by temperature, PAR and leaf area index (LAI) and when increasing these three factors to values found in tropical lowland forest, GPP increased up to 75%. In addition, the modelled results indicate that hydraulic limitations on TMCF C-uptake are very unlikely under current climatic conditions. The modelled results also showed that increases in radiation as a result of less cloud cover do not translate to straightforward increases of GPP. The cloudy conditions of TMCFs, which reduced incident PAR in TMCFs, should therefore not be regarded simply as a negative control on TMCF GPP. Instead, the increase in fraction of diffuse radiation partially offsets the decrease in GPP following the reduction in PAR. Overall, the results of this study show that leaves of Andean TMCF forests have similar C-uptake capacity to tropical lowland rainforests when standardized to similar temperatures, but that for in situ C-uptake temperature, radiation and LAI are the key controls.

Converting solar energyto fuels such as hydrogen by the reaction of water splitting is a promising solution for the future sustainable energy systems. The theme of this thesis is to design water splitting devices via molecular engineering; it concerns the studies of both electrochemical-driven and photo-electrochemical driven molecular functional devices for water splitting. The first chapter presents a general introduction about Solar Fuel Conversion. It concerns molecular water splitting catalysts, light harvesting materials and fabrication methods of water splitting devices. The second chapter describes an electrode by immobilizing a molecular water oxidation catalyston carbon nanotubes through the hydrophobic interaction. This fabrication method is corresponding to the question: “How to employ catalysts in functional devices without affecting their performances?” In the third chapter, molecular water oxidation catalysts were successfully immobilized on glassy carbon electrode surface via electrochemical polymerization method. The O-O bond formation pathways of catalysts on electrode surfaces were studied. This kinetic studyis corresponding to the question: “How to get kinetic information of RDS whena catalyst is immobilized on the electrode surface?” Chapter four explores molecular water oxidation catalysts immobilized on dye-sensitized TiO2 electrodeand Fe2O3 semiconductor electrode via different fabrication methods. The reasons of photocurrent decay are discussed and two potential solutions are provided. These studies are corresponding to the question: “How to improvethe stability of photo-electrodes?” Finally, in the last chapter, two novel Pt-free Z-schemed molecular photo-electrochemical cells with both photoactive cathode and photoactive anode for visible light driven water splitting driven were demonstrated. These studies are corresponding to the question: “How to utilizethe concept of Z-schemein photosynthesis to fabricate Pt-free molecular based PEC cells? / <p>QC 20160129</p>

Tocopherols, collectively known as vitamin E, are lipophilic antioxidants, which are synthesized only by photosynthetic organisms. Due to their enormous potential to protect cells from oxidative damage, tocopherols are used e.g. as nutraceuticals and additives in pharmaceuticals. The most biologically active form of vitamin E is α-tocopherol. Most tocopherols are currently produced via chemical synthesis. Nevertheless, this always results in a racemic mixture of different and less effective stereoisomers because the natural isomer has the highest biological activity. Therefore, tocopherols synthesized in natural sources are preferred for medical purposes. The annual sunflower (Helianthus annuus L.) is a well-known source for α-tocopherol. Within the presented work, sunflower callus and suspension cultures were established growing under photomixotrophic conditions to enhance α-tocopherol yield. The most efficient callus induction was achieved with sunflower stems cultivated on solid Murashige and Skoog medium supplemented with 30 g l-1 sucrose, 0.5 mg l-1 of the auxin 1-naphthalene acetic acid and 0.5 mg l-1 of the cytokinin 6-benzylaminopurine. Photomixotrophic sunflower suspension cultures were induced by transferring previously established callus into liquid medium. The effects of light intensity, sugar concentration and culture age on growth rate and α-tocopherol synthesis rate were characterized. A considerable increase (max. 230 %) of α-tocopherol production in the cells was obtained within the photomixotrophic cell culture compared to a heterotrophic cell culture. These results will be useful for improving α-tocopherol yields of plant in vitro cultures.