Dark respiration rates of the aerial shoots of Arceuthobium tsugense, obtained by manometric and IRGA techniques, show production of C02to range between 155-300 µl CO2 g-1h-1 with evidence of seasonal variation. Experiments with 14C02 indicate that the aerial shoots are capable of some photosynthetic CO2 fixation, with 10-15% of the available 14C incorporated by the plant tissue in one hour.The portions of the o aerial shoots which are most active in C02 fixation are the young terminal regions. Biochemical characterization of the products of photosynthesis reveals that 80-90% of the incorporated 14C is ethanol soluble. Ten percent of the ethanol fraction is lipoidal in nature, the rest is H20 soluble. Ion exchange separation of the H20 soluble portion shows that 16-25% of the 14C activity is cationic, about 25% anionic, with the balance neutral. Aspartic acid, glutamic acid, and valine are present in the cationic fraction, with additional free amino acids indicated. IRGA experiments indicate an apparent photosynthetic CO2 fixation capacity of 80-90 percent of the ethanol fraction is lipoidal in nature, the rest is H20 soluble. Ion exchange separation of the H20 soluble portion shows that 16-25% of the 14C activity is cationic, about 25% anionic, with the balance neutral. Aspartic acid, glutamic acid, and valine are present in the cationic fraction, with additional free amino acids indicated. IRGA experiments indicate an apparent photosynthetic CO2 fixation capacity of 80-90 µl CO2 g-1 h-1, or 25-30% of the amount of C02 produced by respiration. The significance of these findings is discussed with respect to nutrition of the parasite.

Porphyrins derivatized with electron donating and electron withdrawing groups can be used for artificial photosynthesis. Four new compounds, two electron donors and two electron acceptors, have been synthesized for prospective porphyrin linkages.

Net photosynthesis and dark respiration studies were conducted on Atriplex confertifolia (Torr. and Frem.) S. Wats and Ceratoides lanata (Pursh) J.T. Howell under field and laboratory conditions. These woody species are commonly found in salt desert shrub communities of the Intermountain West. During these investigations, the effects of air temperature, plant moisture stress, soil water potential, irradiation, and plant phenological status were examined with respect to their influence on carbon dioxide (CO2 ) exchange. Intensive field studies were carried out between April and October. This interval corresponded to the major period of physiological activity in both species. The factors of moisture stress and phenological status appeared to regulate photosynthesis and respiration on a seasonal basis. They set the limits within which daily CO2 exchange could take place. Diel patterns of CO2 exchange were primarily controlled by prevailing temperature and irradiation. Irradiation was more critical during the spring, and temperature became more limiting in the summer. Two alternate photosynthetic strategies of dealing with existing harsh environmental conditions appeared to have evolved in Atriplex confertifolia and Ceratoides lanata. Atriplex confertifolia exhibited an endurance strategy whereby it continued moderate rates of photosynthesis throughout the season. Ceratoides lanata, in contrast, completed the majority of its net assimilation in the spring; then it was relatively inactive when moisture stress became great. These differences seemed to be correlated with water use efficiencies of both species. Rates of net photosynthesis were greatest during the spring in both species. At that time CO2 fixation in Ceratoides lanata exceeded that of Atriplex confertifolia. Later in the year, photosynthetic rates were reduced; and the assimilation rate of Atriplex confertifolia was greater than that observed in Ceratoides lanata. These seasonal patterns of CO2 exchange offered an insight into differences between species using different assimilation pathways. Atriplex confertifolia utilizes the dicarboxylic acid pathway (C4) for carbon fixation, while Ceratoides lanata uses the pentose pathway (C3). Since both species can coexist in the same reasonably stable community, it appeared that both carboxylation pathways were efficient with respect to prevailing environmental conditions. Atriplex confertifolia had lower net assimilation rates than C4 species from warmer climates. It carried on moderate rates of photosynthesis at low temperature (5 to 10 C), and it had relatively low thermal optima (15 to 27 C) for net photosynthesis. An acclimative shift in temperature optima was also noted. This photosynthetic pattern seemed to be related to the climatic conditions under which Atriplex confertifolia evolved. Ceratoides lanata exhibited assimilation rates which were comparable to other C3 species in arid environments. As with Atriplex confertifolia, Ceratoides lanata carried on photosynthesis at relatively low temperatures, but it did not undergo an acclimative shift in the temperature optimum (15 C). Both species were physiologically adapted to severe moisture stress. They carried out active photosynthesis and respiration at soil water potentials between -15 and -50 bars. As soil water potential decreased below -50 bars, CO2 exchange in Ceratoides lanata was curtailed. Photosynthesis and respiration continued at a moderate level in Atriplex confertifolia until soil water potential was reduced below -70 bars.

No description available.

The atmospheric (CO2) partial pressure is expected to continue to increase and the scenario is that the CO2 partial pressure will reach 50-70 Pa during the 21st century.The rise in CO2 will have a direct influence on plant growth and development because CO2 is the primary substrate for photosynthesis.The aim of the studies described in this thesis was to investigate the response of grasses belonging to two subtypes to a range of CO2 partial pressures under conditions where light intensity, water and N supplies were varied.Two species which are naturalized in Australia, Panicum coloratum (NAD-ME) and Cenchrus ciliaris (NADP-ME) were chosen for a series of experiments conducted in matched growth chambers. The response of C4 plants is particularly important for Australia because they dominate the tropical grasslands that occupy 75% of the continent and form the basis for the pasture industry. Following the extensive research conducted in this study, it can be concluded that the inevitable rise in atmospheric CO2 partial pressure will increase the growth of C4 grasses when other resources are not limiting.Growth of C4 grasses will be stimulated to a greater extent under conditions of drought. / Doctor of Philsophy (PhD)

A variety of unicellular green algae have the ability to photo-produce molecular hydrogen (H2). Using sunlight to power the production of H2 from water is attractive due to the abundant supply of both resources and the potential for the technology to address global warming and energy supply concerns. Increasing levels of H2 production from those currently achievable with algal systems is a necessity for the technology to become economically feasible. Green unicellular algae are rare amongst organisms in that some have an ability to switch to an H2-producing metabolism when environmental conditions become anaerobic. The process of H2 production is greatly accentuated in the light due to the role of the photosynthetic apparatus directing electron flow to hydrogenase enzymes located in the chloroplast. Difficulties in maintaining continuous systems of H2 production largely result from the O2 sensitivity of hydrogenase enzymes. As O2 is generally produced through photosynthesis, the process of H2 production has always been short-lived. Recently, a process of inducing H2 production for several days was accomplished by depriving the growth medium of sulphur (Melis et al., 2000). Lacking sulphur, photosystem II activity diminishes to a point where any O2 evolved is consumed by respiration; this leads to the culture becoming anaerobic and to the onset of H2 production. The method of sulphur depletion has proven to be very useful for studies of H2 production due to enhanced rates over longer time periods being possible. This work was performed to search for new H2-producing Australian algal species and to shed light upon the molecular and biochemical interactions occurring when algal species move from aerobic photosynthetic growth to an anaerobic H2-producing status. An assay to test new species for an H2-producing ability was developed and implemented; leading to the isolation of new H2-producing species from Australian waters. The assay involved purging algal cultures in the dark with N2, sealing them in bioreactors and then exposing them to light. Metabolic profiling performed during this assay revealed cells to rapidly enter a fermentative metabolism upon the onset of anoxia. Acetate, formate and ethanol were key metabolites produced alongside H2 during this period. Metabolomics was used as a tool to understand the biochemical interactions occurring during 120 h of sulphur depleted H2 production. Extraction protocols were developed that allowed the detection and identification of over 100 metabolites using gas chromatography coupled to mass spectrometry, nuclear magnetic resonance spectroscopy and thin layer chromatography. Shifts in primary energy metabolism when cells switch from O2 production to H2 production were revealed. Indications are that both starch and triacylglyceride accumulate during the first 24 h of sulphur depletion prior to anoxia. Following the onset of anoxia, fermentative metabolism begins, H2 is produced and amino acids generally increase. A build-up of toxic fermentative end products and a lack of sulphur are believed to cause the termination of H2 production, rather than a lack of energy reserves. Key achievements of this work have been: • The establishment of an assay that can be used for future bio-prospecting work aimed at finding H2-producing algal species. • The isolation of new H2-producing green algal species from Australian waters. • The establishment of protocols for the extraction of metabolites from small volumes (1 ml) of Chlamydomonas reinhardtii cultures for analysis on a variety of analytical platforms. • The mapping of changes in metabolism of C. reinhardtii during the switch from an aerobic environment to an anaerobic H2-producing environment. • A range of recommendations for future research that may lead to higher H2 production.

<p>This thesis deals with the synthesis and characterisation of a series of dinuclear manganese complexes. Their ability to donate electrons to photo-generated ruthenium(III) has been investigated in flash photolysis experiments followed by EPR-spectroscopy. These experiment shows several consecutive one-electron transfer steps from the manganese moiety to ruthenium(III), that mimics the electron transfer from the oxygen evolving centre in photosystem II.</p><p>The redox properties of these complexes have been investigated with electro chemical methods and the structure of the complexes has been investigated with different X-ray techniques. Structural aspects and the effect of water on the redox properties have been shown.</p><p>One of the manganese complexes has been covalently linked in a triad donor-photosensitizer-acceptor (D–P–A) system. The kinetics of this triad has been investigated in detail after photo excitation with both optical and EPR spectroscopy. The formed charge separated state (D^––P–A⁺) showed an unusual long lifetime for triad based on ruthenium photosensitizers.</p><p>The thesis also includes a study of manganese-salen epoxidation reactions that we believe can give an insight in the oxygen transfer mechanism in the water oxidising complex in photosystem II.</p>

<p>Although low temperature plays an important role in determining agricultural yield, little is known about the effect on the underlying biochemical and physiological processes that influence plant growth. Photosynthesis and respiration are central to plant growth and both processes are heavily affected by temperature. However, many plants have the ability to cope with low temperature and resume growth by cold acclimating.</p><p>We have shown that enhancement of carbon fixation, an increased flux of carbon into sucrose and the recovery of diurnal export is crucial for the recovery of functional carbon metabolism at low temperature in Arabidopsis thaliana. The recovery of efflux is governed by increased expression of sucrose transporters along with changes in vascularisation. We also demonstrate the importance of controlling the flux of metabolites between the chloroplast and the cytosol by regulating the expression of AtTPT.</p><p>We further investigated the difference in response between leaves developed at low temperature but originating from warm grown Arabidopsis and leaves from plants grown from seed at low temperature. We were able to distinguish factors that respond specifically to low temperature from those that are connected to the actual stress. Substantial difference could be seen in the different metabolomes. One conclusion drawn is that the increase in sucrose reported at low temperature is an essential feature for life in the cold. </p><p>In an extended study we were able to transfer some of the key factor of cold acclimation in Arabidopsis to other species. The study included forbs, grasses and evergreen trees/shrubs showed that there are striking similarities in the extent and biochemical changes that underpin acclimation among the different functional groups.</p><p>Low temperature does not only influence growth of the leaves, perennial organs such as the corm of the ornamental plant Crocus vernus is also affected. However in these plants low temperature has a positive effect on the final size of the corm. We were able to show that this enhanced growth was an affect of increased cell size and thus increased sink capacity, which ultimately delays leaf senescence</p>

<p>In natural oxygen-producing photosynthesis solar energy is stored as chemical energy, in carbohydrates, fats and amino acids, using water as electron source. The large transmembrane protein complex, PSII, is the key enzyme in the light-driven reactions. Water oxidation is accomplished by a triad in PSII in which the Mn-cluster plays an important role. In the artificial photosynthetic system, nature’s photosynthesis will be mimicked such that hydrogen, a sustainable energy source, can be produced from solar energy and water alone. Since water oxidiation requires the catalytic activity of a Mn-cluster in photosynthesis, different artificially constructed manganese complexes are investigated. </p><p>The dinuclear ([Mn₂(II,III)L(µ-OAc)₂]ClO₄), where L is the X-anion of 2-(<i>N,N</i>-Bis(2-methylpyridyl)aminomethyl)-6-(<i>N</i>-(3,5-ditert-butylbenzyl-2-hydroxy)-<i>N</i>-(pyridylmethyl)aminomethyl)-4-methylphenol, an unsymmetric ligand with two coordinating phenolate groups, has been studied. The two Mn-ions are linked via a mono-µ-oxo bridge and two acetate ligands. Q-band Electron Paramagnetic Resonance was conducted on the Unsymmetric Mn₂(II,III) Complex. Aquired results show that the complex has a 2600 Gauss broad signal (11 400-14 000 Gauss) with 14-17 lines at g~2 and hyperfines of 120 Gauss. This is consistent with previous X-band studies. Q-band spectra of the Unsymmetric Mn(II,III) display increased hyperfine resolution compared to Qband spectra of the symmetric complex, Mn₂(bpmp)(µ-OAC)₂. This is noticeable since Unsymmetric Mn2(II,III) and Mn₂ (bpmp)(µ-OAC)₂ partly overlap in low-frequency experiments (X-band EPR). </p><p>Further investigations are yet to be expected. Nevertheless, the conducted thesis study provides important knowledge in the futuristic goal of building an artificial super-complex.</p>

<p>In this study I will find out which thoughts and alternative conceptions pupils have about photosynthesis, decomposing and breeding. The method used was qualitative semi-structured interviews with pupils in preschool class and in the third grade. They were interviewed about what a flower needs in order to live, die and to propagate themselves. The result shows that the students have alternative conceptions about these issues. There are no big differences in the notions of the average classes. There is a relation between the children’s way of living and their notions.</p><p>The result shows that all 17 pupils know that the flowers need water and soil. Half of them know that it also needs sun. But only 2 pupils know that the flowers need sugar to live.</p>