EPR spectroscopy and isotopic substitution were used to gain increased knowledge about the proton-coupled electron transfer (PCET) mechanism for the reduction of the tyrosine D radical (YD*) in photosystem II. pL dependence (where pL is either pH or pD) of both the rate constant and kinetic isotope effect (KIE) was examined for YD* reduction. Second, the manner in which protons are transferred during the rate-limiting step for YD* reduction at alkaline pL was determined. Finally, high field electron paramagnetic resonance (EPR) spectroscopy was used to study the effect of pH on the environment surrounding both the tyrosine D radical and the tyrosine Z radical (YZ*). At alkaline pL, it was determined that the proton and electron are both transferred in the rate-limiting step of YD* reduction. At acidic pL, the proton transfer occurs first followed by electron transfer. Proton inventory experiments indicate that there is more than one proton donation pathway available to YD* during PCET reduction at alkaline pL. Additionally, the proton inventory experiments indicate that at least one of those pathways is multiproton. High field EPR experiments indicate that both YD* and YZ* are hydrogen bonded to neutral species. The EPR gx component for YD* is invariant with respect to pH. Analysis of the EPR gx component for Yz* indicates that its environment becomes more electropositive as the pH is increased. This is most likely due to changes in the hydrogen bond strength

Processes where a molecule absorbs visible light and then converts the solar energy into chemical energy are important in many biological systems, such as photosynthesis and also in many technical applications e.g. photovoltaics. This thesis describes a part of a multidisciplinary project, aiming at a functional mimic of the natural photosynthesis, with the overall goal of production of a renewable fuel from sun and water. More specific, the thesis is focused on design and photophysical characterization of new photosensitizers, i.e. light absorbers that should be capable of transferring electrons to an acceptor and be suitable building blocks for supramolecular rod-like donor-photosensitizer-acceptor arrays. The excited state lifetime, the excited state energy and the geometry are important properties for a photosensitizer. The work presented here describes a new strategy to obtain longer excited state lifetimes of the geometrically favorable Ru(II)-bistridentate type complexes, without a concomitant substantial decrease in excited state energy. The basic idea is that a more octahedral coordination around the Ru will lead to longer excited state lifetimes. In the first generation of new photosensitizers a 50-fold increase of the excited state lifetime was observed, going from 0.25 ns for the model complex to 15 ns for the best photosensitizer. The second generation goes another step forward, to an excited state lifetime of 810 ns. Furthermore, the third generation of new photosensitizers show excited state lifetimes in the 0.45 - 5.5 microsecond region at room temperature, a significant improvement. In addition, the third generation of photosensitizers are suitable for further symmetric attachment of electron donor and acceptor motifs, and it is shown that the favorable properties are maintained upon the attachment of anchoring groups. The reactivity of the excited state towards light-induced reactions is proved and the photostability is sufficient so the new design strategy has proven successful.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 1930" Heather Marie Netzloff. 12/19/2004. Report is also available in paper and microfiche from NTIS.

Παρά τη σημαντική της συνεισφορά στο συνολικό κέρδος σε άνθρακα των φυτών και τις λειτουργικές της ιδιαιτερότητες, η φωτοσύνθεση βλαστού δεν έχει μελετηθεί στην έκταση που της αναλογεί. Για το λόγο αυτό εφαρμόσαμε ένα συνδυασμό ανατομικών και φυσιολογικών μεθόδων για το χαρακτηρισμό του φωτοσυνθετικού μηχανισμού των πράσινων μίσχων και των στελεχών του άνθους του μονοκοτυλήδονου γεώφυτου Zantedeschia aethiopica και των πράσινων βλαστών του δικοτυλήδονου ημιξυλώδους Dianthus caryophyllus, σε σύγκριση με τα αντίστοιχα φύλλα. Οι μίσχοι και τα στελέχη του άνθους του Z. aethiopica και οι βλαστοί του D. caryophyllus διαθέτουν όλα τα ανατομικά χαρακτηριστικά ενός φωτοσυνθετικά αποδοτικού οργάνου, όπως σημαντικό αριθμό στομάτων με τυπικούς υποστομάτιους θαλάμους, χλωρεγχυματικά κύτταρα παρόμοιας μορφολογίας με τα δρυφακτοειδή κύτταρα των φύλλων, επαρκείς μεσοκυττάριους χώρους και σημαντικό ποσοστό ελεύθερων κυτταρικών τοιχωμάτων. Ωστόσο, η διάταξη των δρυφακτοειδών κυττάρων των μίσχων/στελεχών του Z. aethiopica είναι ασυνήθιστη, καθώς διευθετούνται παράλληλα με τον κατά μήκος άξονα των οργάνων. Επιπλέον, οι μίσχοι/στελέχη επέδειξαν φωτοσυνθετικά χαρακτηριστικά που προσομοιάζουν με εκείνα φύλλων σε συνθήκες καταπόνησης, όπως μειωμένο περιεχόμενο/ενεργότητα της Rubisco, αυξημένο ρυθμό του κύκλου C2 και αυξημένη κυκλική ροή ηλεκτρονίων γύρω από το PSI. Τα χαρακτηριστικά αυτά φαίνεται πως είναι εγγενή στα συγκεκριμένα φωτοσυνθετικά όργανα, εξυπηρετώντας την αυξημένη αζωτοδεσμευτική ικανότητα του είδους, την ποιοτική ρύθμιση του περιεχομένου τους σε αμινοξέα, την αποκαρβοξυλίωση C4-οργανικών οξέων του διαπνευστικού ρεύματος και την ταχεία επαγωγή της μη-φωτοχημικής απόσβεσης. Σε αντίθεση με το Z. aethiopica, η φωτοσυνθετική απόδοση των βλαστών του D. caryophyllus βρέθηκε ανώτερη αυτής των φύλλων, ως αποτέλεσμα των υψηλότερων ρυθμών του κύκλου C3 και μιας πιθανής οργανο-ειδικής ποικιλότητας του παράγοντα εξειδίκευσης της Rubisco. Η μειωμένη ένταση του προσπίπτοντος φωτός in vivo, λόγω του κάθετου προσανατολισμού των βλαστών, ενδεχομένως να οδηγεί σε χαμηλότερα επίπεδα φωτοπροστασίας σε σύγκριση με τα φύλλα και στην υιοθέτηση μιας στρατηγικής βελτιστοποίησης του ρυθμού καθήλωσης C, η οποία πιθανώς περιλαμβάνει και την καθήλωση CO2, που προέρχεται από την αποκαρβοξυλίωση C4-οργανικών οξέων του διαπνευστικού ρεύματος. / Despite its significant contribution to the net carbon gain of plants and its distinct functional properties, stem photosynthesis has not yet received adequate scientific attention. For this reason, a combination of anatomical and physiological methods was used to characterize the photosynthetic machinery of the green petioles and pedicels of the monocotyledonous geophyte Zantedeschia aethiopica and the green stems of the dicotyledonous semi-woody species Dianthus caryophyllus, in comparison to the corresponding leaves. Both the green petioles/pedicels of Z. aethiopica and the green stems of D. caryophyllus possess all the anatomical prerequisites of an actively photosynthesizing organ i.e. considerable number of stomata with typical underlying substomatal chambers, chlorenchyma cells which are similar to the leaf palisade chlorenchyma cells and considerable amount of both intercellular spaces and palisade free cell walls. Yet, the palisade cells of Z. aethiopica petioles/pedicels show a peculiar arrangement with their long axis parallel to the longitudinal organ axis. Furthermore, petiole/pedicel photosynthetic characteristics resemble those of leaves under adversity i.e. reduced Rubisco activity/content, high photorespiration rates and significant cyclic electron flow around PSI. It is concluded that these are innate attributes of petiole/pedicel photosynthesis serving particular functions like the increased nitrogen fixing activity of the species, the qualitative adjustment of the petiole/pedicel amino acid content, the active decarboxylation of C4-organic acids and the rapid induction of non-photochemical quenching. Stem photosynthesis in D. caryophyllus was more efficient than leaf photosynthesis, as a result of the greater rates of stem C3 cycle and a possible organ-specific variation of the specificity factor of Rubisco. In general, D. caryophyllus stems display a photosynthetic pattern of optimal carbon assimilation in the expense of photoprotection. It could be hypothesized that this kind of adaptation could be due to the vertical orientation of stems, which results in lower incident light intensities in vivo and may include the use of C4-organic acids coming up with the transpiration stream as an additional carbon source.

Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in aquatic and terrestrial food webs as monomethylmercury (MeHg). Anaerobic microbes are largely responsible for MeHg production, which depends on the bioavailability of inorganic Hg substrates to methylators. Hg redox cycling pathways such as Hg reduction play a key role in determining Hg’s availability in the environment. Although abiotic photochemical Hg reduction typically dominates in oxic surface environments, Hg reduction pathways mediated by photosynthetic and anaerobic microbes are thought to play an important role in anoxic habitats where light is limited and MeHg production occurs. Currently, the physiological mechanisms driving phototrophic and anaerobic Hg reduction remain poorly understood. The main objective of my thesis is to provide mechanistic details on novel anaerobic and phototrophic Hg reduction pathways. I used a combination of physiological, biochemical and trace Hg analytical techniques to study Hg reduction pathways in a variety of anaerobic and photosynthetic bacteria. I demonstrated that Hg redox cycling was directly coupled to anoxygenic photosynthesis in aquatic purple non-sulphur bacteria that reduced HgII when cells incurred a redox imbalance. I discovered that terrestrial fermentative bacteria reduced Hg through pathways that relied on the generation of reduced redox cofactors. I also showed that sulphur assimilation controlled Hg reduction in an anoxygenic phototroph isolated from a rice paddy. In addition, I developed methods to explore cryptic anaerobic Hg redox cycling pathways using Hg stable isotope fractionation. At its core, my thesis underscores the intimate relationship between cell redox state and microbial Hg reduction and suggests a wide diversity of microbes can participate in anaerobic Hg redox cycling.

Made available in DSpace on 2016-08-12T19:15:30Z (GMT). No. of bitstreams: 1 MaykyFPL_Dissert.pdf: 583480 bytes, checksum: b5156cac19b83224804fef6b4df642d2 (MD5) Previous issue date: 2015-02-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / There is no doubt that the effect of weed causes damage to various human activities and especially those for agricultural use. Therefore, if not properly handled, can reduce productivity and production quality due to competition for light, nutrients, and especially water, which is the most abundant resource, while the most limiting to agricultural productivity. This study aimed to assess the potential for competition four weed species by water. The experiment was conducted in a factorial 4 x 2, distributed in a randomized complete block design, with five replications. were studied species malva-branca (Waltheria indica L.); crotalária (Crotalaria retusa L.); mussambê (Cleome affinis DC.) and trapoeraba (Commelina benghalensis L.), with two water regimes (with and without water stress). Plants subjected to water stress had suspended irrigation during flowering, and maintained until the CO2 assimilation rate of plants to morning 9am reached values close to zero, at the resumed irrigation. As from the date irrigation suspension the plants were submitted to the following evaluations: water potential before dawn (ΨAM) and water potential at noon (ΨMD) (MPa); photosynthesis (A; CO2 μmol m-2); stomatal conductance (gs; μmol H2O m-2 s-1), and transpiration (E; mmol H2O m-2 s-1) carried out every day until the photosynthetic rates of plants subjected to water stress is to equalize plants without stress. At the end of the experiment was measured leaf area (cm2), the dry mass of roots, stems, leaves and total (g), the chlorophyll content index near the apex of the leaves and the next leaves the base. Was also determined daily water consumption species (mL). The results grouped the plants into two groups: trapoeraba and mussambê, considered conservative, keeping the high water potential and transpiration, being uncompetitive by water, and crotalária and malva-branca, medium investors, able to reduce the water potential and stomatal aperture values higher, resulting in greater potential for competition for water. And in low water availability conditions, the mauve-white is the most competitive for water, because it can maintain high water consumption levels over time / Não há dúvidas de que a interferência das plantas daninhas causa prejuízos a diversas atividades do ser humano e principalmente aquelas destinadas à agricultura. Por isso, se não forem manejadas adequadamente, podem reduzir a produtividade e a qualidade da produção, devido à competição por luz, nutrientes e principalmente água, que é o recurso mais abundante e, ao mesmo tempo, o mais limitante à produtividade agrícola. O presente trabalho teve como objetivo avaliar o potencial de competição de quatro espécies de plantas daninhas por água. O experimento foi conduzido no esquema fatorial 4 x 2, distribuídos no delineamento experimental em blocos casualizados, com cinco repetições. Foram estudadas as espécies malva-branca (Waltheria indica L.); crotalária (Crotalaria retusa L.); mussambê (Cleome affinis DC.) e trapoeraba (Commelina benghalensis L.)], com dois regimes hídricos (com e sem estresse hídrico). As plantas submetidas ao estresse hídrico tiveram a irrigação suspensa por ocasião do florescimento, e mantida até a taxa de assimilação de CO2 das plantas às 9h da manhã atingisse valores próximos a zero, quando foi retomada a irrigação. A partir da data da suspensão da irrigação as plantas foram submetidas às seguintes avaliações: potencial hídrico antes do amanhecer (ΨAM) e potencial hídrico ao meio dia (ΨMD) (MPa); fotossíntese (A; μmol CO2 m-2); condutância estomática (gs; μmol H2O m-2 s-1), e a transpiração (E; mmol H2O m-2 s-1) realizadas todos os dias até que as taxas de fotossíntese das plantas submetidas ao estresse hídrico se igualassem à das plantas sem estresse. Ao final do experimento foi mensurada a área foliar (cm2), a massa seca das raízes, caules, folhas e total (g), o Índice de conteúdo de clorofila das folhas próximas ao ápice e das folhas próximas a base. Também foi determinado o consumo de água diário das espécies (mL). Os resultados permitiram agrupar as plantas em dois grupos: trapoeraba e mussambê, consideradas como conservadoras, mantendo o potencial hídrico alto e com baixa transpiração, sendo pouco competitivas por água, e crotalária e malva-branca, medianamente investidoras, capazes de reduzir o potencial hídrico e com valores de abertura estomática mais altos, implicando em maior potencial de competição por água. E em condições de baixa disponibilidade de água, a malva-branca é a mais competitiva por água, pois consegue manter altos valores de consumo de água por mais tempo

Made available in DSpace on 2016-08-12T19:18:48Z (GMT). No. of bitstreams: 1 MaykyFPL_Dissert.pdf: 583480 bytes, checksum: b5156cac19b83224804fef6b4df642d2 (MD5) Previous issue date: 2015-02-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / There is no doubt that the effect of weed causes damage to various human activities and especially those for agricultural use. Therefore, if not properly handled, can reduce productivity and production quality due to competition for light, nutrients, and especially water, which is the most abundant resource, while the most limiting to agricultural productivity. This study aimed to assess the potential for competition four weed species by water. The experiment was conducted in a factorial 4 x 2, distributed in a randomized complete block design, with five replications. were studied species malva-branca (Waltheria indica L.); crotalária (Crotalaria retusa L.); mussambê (Cleome affinis DC.) and trapoeraba (Commelina benghalensis L.), with two water regimes (with and without water stress). Plants subjected to water stress had suspended irrigation during flowering, and maintained until the CO2 assimilation rate of plants to morning 9am reached values close to zero, at the resumed irrigation. As from the date irrigation suspension the plants were submitted to the following evaluations: water potential before dawn (ΨAM) and water potential at noon (ΨMD) (MPa); photosynthesis (A; CO2 μmol m-2); stomatal conductance (gs; μmol H2O m-2 s-1), and transpiration (E; mmol H2O m-2 s-1) carried out every day until the photosynthetic rates of plants subjected to water stress is to equalize plants without stress. At the end of the experiment was measured leaf area (cm2), the dry mass of roots, stems, leaves and total (g), the chlorophyll content index near the apex of the leaves and the next leaves the base. Was also determined daily water consumption species (mL). The results grouped the plants into two groups: trapoeraba and mussambê, considered conservative, keeping the high water potential and transpiration, being uncompetitive by water, and crotalária and malva-branca, medium investors, able to reduce the water potential and stomatal aperture values higher, resulting in greater potential for competition for water. And in low water availability conditions, the mauve-white is the most competitive for water, because it can maintain high water consumption levels over time / Não há dúvidas de que a interferência das plantas daninhas causa prejuízos a diversas atividades do ser humano e principalmente aquelas destinadas à agricultura. Por isso, se não forem manejadas adequadamente, podem reduzir a produtividade e a qualidade da produção, devido à competição por luz, nutrientes e principalmente água, que é o recurso mais abundante e, ao mesmo tempo, o mais limitante à produtividade agrícola. O presente trabalho teve como objetivo avaliar o potencial de competição de quatro espécies de plantas daninhas por água. O experimento foi conduzido no esquema fatorial 4 x 2, distribuídos no delineamento experimental em blocos casualizados, com cinco repetições. Foram estudadas as espécies malva-branca (Waltheria indica L.); crotalária (Crotalaria retusa L.); mussambê (Cleome affinis DC.) e trapoeraba (Commelina benghalensis L.)], com dois regimes hídricos (com e sem estresse hídrico). As plantas submetidas ao estresse hídrico tiveram a irrigação suspensa por ocasião do florescimento, e mantida até a taxa de assimilação de CO2 das plantas às 9h da manhã atingisse valores próximos a zero, quando foi retomada a irrigação. A partir da data da suspensão da irrigação as plantas foram submetidas às seguintes avaliações: potencial hídrico antes do amanhecer (ΨAM) e potencial hídrico ao meio dia (ΨMD) (MPa); fotossíntese (A; μmol CO2 m-2); condutância estomática (gs; μmol H2O m-2 s-1), e a transpiração (E; mmol H2O m-2 s-1) realizadas todos os dias até que as taxas de fotossíntese das plantas submetidas ao estresse hídrico se igualassem à das plantas sem estresse. Ao final do experimento foi mensurada a área foliar (cm2), a massa seca das raízes, caules, folhas e total (g), o Índice de conteúdo de clorofila das folhas próximas ao ápice e das folhas próximas a base. Também foi determinado o consumo de água diário das espécies (mL). Os resultados permitiram agrupar as plantas em dois grupos: trapoeraba e mussambê, consideradas como conservadoras, mantendo o potencial hídrico alto e com baixa transpiração, sendo pouco competitivas por água, e crotalária e malva-branca, medianamente investidoras, capazes de reduzir o potencial hídrico e com valores de abertura estomática mais altos, implicando em maior potencial de competição por água. E em condições de baixa disponibilidade de água, a malva-branca é a mais competitiva por água, pois consegue manter altos valores de consumo de água por mais tempo

Native to Europe and Asia, Lythrum salicaria is an invasive element on some other continents. Plants in the invaded areas are more robust, higher, and generally more successful compared to individuals in their original area. Based on my results these characteristics cannot be explained by neither higher photosynthesis, chlorophyll and carotenoid mass, nor specific leaf area.