Biofuel production from microalgal biomass offers a clean and sustainable liquid fuel alternative to fossil fuels. In addition, algae cultivation is advantageous over traditional biofuel feedstocks as (i) it does not compete with food production, (ii) it potentially has a much greater areal productivity, (iii) it does not require arable land, and (iv) it can use marginal sources of water not suitable for irrigation or drinking. However, current algae cultivation technologies suffer from (i) low solar energy conversion effiencies, (ii) large thermal fluctuations which negatively affect the productivity, and (iii) large evaporative losses which make the process highly water intensive. This thesis reports a numerical study that address these key issues of planktonic as well as benthic algal photobioreactor technologies. First, radiant energy transfer in planktonic algal photobioreactors containing cells with different levels of pigmentation was studied. Chlamydomonas reinhardtii and its truncated chlorophyll antenna transformant tla1 were used as model organisms. Based on these simulations guidelines are derived for scaling the size and microorganism concentration of photobioreactors cultivating cells with different levels of pigmentation to achieve maximum photosynthetic productivity. To achieve this, the local irradiance obtained from the solution of the radiative transport equation (RTE) was coupled with the specific photosynthetic rates of the microorganisms to predict both the local and total photosynthetic rates in a photobioreactor. For irradiances less than 50 W/m2, the use of genetically modified strains with reduced pigmentation was shown to have negligible effect on increasing photobioreactor productivity. However, at irradiances up to 1000 W/m2, improvements of up to 30% were possible with cells having 63% less pigment concentration. It was determined that the ability of tla1 to transmit light deeper into the photobioreactor was the primary mechanism by which a photobioreactor using the modified strain can achieve greater productivity. Furthermore, it was determined photobioreactors using each strain have dead zones in which the local photosynthetic rate is negligible due to nearly complete light attenuation. These dead zones occur at local optical thicknesses greater than 169 and 275 in photobioreactors using the wild strain and the genetically modified strain, respectively. In addition, a thermal model of an algae biofilm photobioreactor was developed to assess the thermal fluctuations and evaporative loss rate of these novel photobioreactors under varying outdoor conditions. The model took into account air temperature, irradiance, relative humidity, and wind speed as inputs and computed the temperature and evaporative loss rate as a function of time and location in the photobioreactor. The model was run for a week-long period in each season using weather data from Memphis, TN. The range of the daily algae temperature variation was observed to be 13.2C, 12.4C, 12.8C, and 9.4C in the spring, summer, winter, and fall, respectively. Furthermore, without active cooling, the characteristic evaporative water loss from the system is approximately 6.3 L/m2-day, 7.0 L/m2-day, 4.9 L/m2-day, and 1.5 L/m2-day in the spring, summer, fall, and winter, respectively. / text

No description available.

The cyclic nucleotide monophosphates (CNs), cAMP and cGMP, are second messengers that participate in the regulation of development, metabolism and adaptive responses. In plants, CNs are associated with the control of pathogen responses, pollen tube orientation, abiotic stress response, membrane transport regulation, stomatal movement and light perception. In this study, we hypothesize that cAMP and cGMP promote changes in the transcription level of genes related to photosynthesis, high light and membrane transport in Arabidopsis thaliana leaves and, that these changes at the molecular level can have functional biological consequences. For this reason we tested if CNs modulate the photosynthetic rate, responses to high light and root ion transport. Real time quantitative PCR was used to assess transcription levels of selected genes and infrared gas analyzers coupled to fluorescence sensors were used to measure the photosynthetic parameters. We present evidence that both cAMP and cGMP modulate foliar mRNA levels early after stimulation. The two CNs trigger different responses indicating that the signals have specificity. A comparison of proteomic and transcriptional changes suggest that both transcriptional and post-transcriptional mechanisms are modulated by CNs. cGMP up-regulates the mRNA levels of components of the photosynthesis and carbon metabolism. However, neither cAMP nor cGMP trigger differences in the rate of carbon assimilation, maximum efficiency of the photosystem II (PSII), or PSII operating efficiency. It was also demonstrated that CN regulate the expression of its own targets, the cyclic nucleotide gated channels - CNGC. Further studies are needed to identify the components of the signaling transduction pathway that mediate cellular changes and their respective regulatory and/or signaling roles.

No description available.

The studies presented in this thesis explore electronic energy transfer (EET) in light-harvesting antenna complexes and investigate the role of quantum coherence in EET. The dynamics of energy transfer are investigated in three distinct length scales and a different formulation of the exciton transport problem is applied at each scale. These scales include: the scale of a molecular dimer, the scale of a single protein and the scale of a molecular aggregate. The antenna protein phycoerythrin 545 (PE545) isolated from the photosynthetic cryptophyte algae Rhodomonas CS4 is specifically studied in two chapters of this thesis. It is found that formation of small aggregates delocalizes the excitation across chromophores of adjacent proteins, and that this delocalization has a dramatic effect in enhancing the rate of energy transfer between pigments. Furthermore, we investigate EET from a donor to an acceptor via an intermediate site and observe that interference of coherent pathways gives a finite correction to the transfer rate that is sensitively dependent on the nature of the vibrational interactions in the system. The statistical fluctuations of a system exhibiting EET are investigated in the final chapter. The techniques of non-equilibrium statistical mechanics are applied to investigate the steady-state of a typical system exhibiting EET that is perturbed out of equilibrium due to its interaction with a fluctuating bath.

The studies presented in this thesis explore electronic energy transfer (EET) in light-harvesting antenna complexes and investigate the role of quantum coherence in EET. The dynamics of energy transfer are investigated in three distinct length scales and a different formulation of the exciton transport problem is applied at each scale. These scales include: the scale of a molecular dimer, the scale of a single protein and the scale of a molecular aggregate. The antenna protein phycoerythrin 545 (PE545) isolated from the photosynthetic cryptophyte algae Rhodomonas CS4 is specifically studied in two chapters of this thesis. It is found that formation of small aggregates delocalizes the excitation across chromophores of adjacent proteins, and that this delocalization has a dramatic effect in enhancing the rate of energy transfer between pigments. Furthermore, we investigate EET from a donor to an acceptor via an intermediate site and observe that interference of coherent pathways gives a finite correction to the transfer rate that is sensitively dependent on the nature of the vibrational interactions in the system. The statistical fluctuations of a system exhibiting EET are investigated in the final chapter. The techniques of non-equilibrium statistical mechanics are applied to investigate the steady-state of a typical system exhibiting EET that is perturbed out of equilibrium due to its interaction with a fluctuating bath.

Seasonal priorities for the use of current photosynthate were studied in the leaves of Betula glandulosa Michx. and Ledum groenlandicum Oeder from northern Quebec. A sequential extraction scheme was developed to separate ('14)C-labelled leaf tissues into several classes of organic compounds. Data were analysed in terms of carbon use priority (CUP) defined as the ('14)C activity in a compound category as percentage of the total activity in the leaf. / Developing leaves represented the strongest sink for current photosynthate among evergreen leaf age classes. In both species the priorities for structural components, leaf protection and metabolic components decreased while the importance of cellular lipids and storage carbohydrates increased with leaf age. The deciduous leaves had higher overall carbon use priorities for metabolic components, cellular lipids and storage carbohydrates. The priorities for structural components and leaf protection were higher in the evergreen leaves. Leaf protection was an important consideration in both species. Both B. glandulosa and L. groenlandicum leaves (1) allocated photosynthate to antiherbivore compounds when leaf succeptibility was highest, (2) used both quantitative and qualitative type defenses, and (3) reduced carbon use for quantitative type defenses during active growth.

A semi-herbaceous. pioneer plant Chryzanihtmoidts moniiifera was grown under varying environmental condition; in order to assess whether altering environmental variables would affect its hydraulic conductance and photo synthetic rates The plants were grown under sun and shade conditions, subjected to low and high watering treatments and to two different nutrient regimes. Steady-state gaseous exchange parameters, and whole-plant and leaf hydraulic conductance were measured on plants from each treatment. A key aspect of this study was to investigate how the following leaf components - petiole. major veins, minor veins and extravascular tissue - contributed to die overall resistance to water flow in the leaf (Ricaf). Vein orders were cut in specific sequences to interrupt water flow which then allowed the partitioning of leaf hydraulic resistances. The results showed that die maximum pbotosynthetic rate, under light saturating CO;. (A,^ was significantly affected by both nutrient and light treatments Environmental conditions (light, water and nutrient treatments) did not. however, affect the CO.- compensation point, or dark respiration of the measured A:C, curves for C. moniaftra. In terms of whole-plant hydraulic conductance, the shoot, stem and root were not significantly affected by environmental treatments. When investigating R«„. only the light treatments significantly affected the resistance of the petiole, extra vascular tissue, and minor vans Rf<trfc was found to be positively correlated with and contributed between 34-59 % of the total leaf resistance When considering the resistance of the leaf it was observed that the vascular tissue of the leaf contained up to 90 % of the total leaf resistance. The results from this study show that the hydraulic conductance of C. moniijfera was found to be significantly affected by light treatment; only. Water and nutrient treatments did not have a substantial impact upon the water flow of the plant. Leaf hydraulic resistance was partitioned differently to that of results from ocher studies, in that the petiole and major veins contained the majority of the leaf resistance In retrospect this study would have been more effective if C. monilitfera treatments were more severe, in terms of water and nutrients Further studies should focus on a comparison of leaf hydraulic resistance partitioning of other species, across a range of plant types. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2008.

Isoprene is the most abundant volatile organic compound (VOC) emitted from vegetation, mainly trees. Because it plays an important role in tropospheric chemistry leading to formation of pollutants and enhancing the lifetime of the greenhouse gas methane, concern about the response of isoprene emissions to the rise in atmospheric CO2 concentration and global climate change has been increasing over the last few years. The consequences of predicted climate change will have complex repercussions on global isoprene emission. The increasing atmospheric CO2 per se will have direct effects on terrestrial vegetation since CO2 is the substrate of photosynthesis. Because photosynthesis is limited by CO2 at current ambient concentrations, an increase in CO2 is expected to increase leaf biomass (i.e. isoprene emitting surface). Predicted warmer climate, extended drought periods, the possible shift in plant species in favour of isoprene emitters and the increase in length of growing season, may cause an increase in global isoprene emissions with profound perturbations of air quality and the global carbon cycle. The aim of this thesis was to investigate the effect of environmental variables such as light, temperature, drought and leaf-to-air vapour pressure deficit (VPD), and the short- and long-term effect of atmospheric [CO2] on isoprene emission from temperate and tropical tree species. Both leaf and whole ecosystem level fluxes were studied. At the leaf scale, a short-term experiment with leaves of potted two-year old trees of Quercus virginiana was carried out, exposing plants to two drying-rewatering cycles. Leaf isoprene emission fell, but the process was considerably less sensitive to water stress than photosynthesis and stomatal conductance. In drought conditions, the large reduction in photosynthesis caused the percentage of fixed carbon lost as isoprene to increase as plants became more stressed, reaching peaks of 50% when photosynthesis was almost zero. Isoprene emissions also showed a strong negative linear relationship with pre-dawn leaf water potential (psi-leaf). In another experiment carried out at the large enclosed facility of Biosphere 2 (B2L, Arizona, USA), studying isoprene emission from leaves of three-year-old plants of Populus deltoides grown at three CO2 atmospheric concentrations (430, 800 and 1200 mu mol mol-1 CO2) in non-stressed conditions, instantaneous increases in atmospheric [CO2] always resulted in a reduction of isoprene emission and a stimulation of photosynthesis. Moreover, in the long-term, the CO2 inhibition effect for isoprene emission became a permanent feature for plants growing under elevated [CO2]. Again, isoprene emission was less responsive to drought than photosynthesis. Both water-stress and high VPD strongly stimulated isoprene emission and depressed photosynthetic rate as a result of stomatal closure and the resulting decreases in intercellular [CO2] (Ci). This also led to a dramatic increase in the proportion of assimilated carbon lost as isoprene. The effect of atmospheric elevated [CO2] and its interaction with high VPD and water stress on ecosystem gross isoprene production (GIP) and net ecosystem exchange of CO2 (NEE) in the Populus deltoides plantations was also studied. Although GIP and NEE showed a similar response to light and temperature, NEE was stimulated by elevated CO2 by 72% and depressed by high VPD, while GIP was inhibited by elevated CO2 by 58% and stimulated by high VPD. Similar to what was observed at leaf level, under water stress conditions GIP was stimulated in the short term and declined only when the stress was severe, whereas NEE started to decrease from the beginning of the experiment. This contrasting response led the percentage of assimilated carbon lost by the ecosystem as isoprene to increase as water stress progressed from 2.5% and 0.6% in well-watered conditions to 60% and 40% for the ambient and the elevated CO2 treatments, respectively. Again, we found water limitation and high VPD off-set the inhibitory effect of elevated CO2, leading to increased isoprene emissions. The effect of a mild water stress on GIP and gross primary production (GPP) was also observed in the model tropical rainforest mesocosm of B2L. Although GPP was reduced by 32% during drought, GIP was not affected and correlated very well with both light and temperature. The percentage of fixed C lost as isoprene tended to increase during drought because of the reduction in GPP. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter-free soil of the agroforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric [CO2]. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. In summary, elevated CO2 increased biomass production and photosynthesis while depressing isoprene production. However, both drought and VPD may off-set the CO2 effect and lead to enhanced isoprene emission. We conclude that the overall effect of global climate change could be of enhancing global isoprene emissions while depressing the soil sink, and that the soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget.

Photosynthetic membranes were prepared from the cyanobacterium Synechococcus PCC 7942 with oxygen evolving specific activity of 250-300 µmoles 02/ mg chl/hr. The membranes retained activity with a half-life of 4-5 days when stored at 0°C, or when quickly frozen in liquid nitrogen, greater than 95% of the activity remained after 2 months. Attempts to purify homogeneous preparations of photosystem II complexes from these membranes by detergent extraction were unsuccessful as indicated by a lack of a significant increase in oxygen evolution specific activity of the detergent extracts. Photosynthetic membrane detergent extracts usually maintained the same oxygen evolution specific activity as the orginal membranes, and a considerable amount of Photosystem I activity (75 µmoles 02 consumed /mg chl/hr in the Mehler reaction) was still present. The donor side of the photosystem II particles in the detergent extract was intact since the artificial electron acceptor, 2,6-dichiorophenolindophenol (DCPIP), was reduced at a rate comparable to the oxygen evolving activity. All oxygen evolving activity of the detergent extracts was lost when ion-exchange chromatography was used to resolve the co-extracted photosystem II and photosystem I complexes. / Department of Biology