No description available.

Graduation date: 1997

Globally, an estimated 25% of the CO2 and 90% of the N2O is believed to come from agroecosystems. The objective of this study was to investigate the dynamics of the below-ground CO 2 and N2O concentrations and efflux in corn and soybean systems. In our field study, changes in the below-ground concentrations of CO 2 and N2O were closely related to seasonal changes in soil moisture, with the first two months of the growing season being particularly critical to the production of these gases. Tillage significantly increased CO2 content in the soil profile, however, this effect was greater in the soybean plots than in the corn plots. In our greenhouse studies, an average of about 79% of the soil respiration in corn came from rhizosphere respiration, compared to an estimated 58% in the case of soybean. Specific rhizosphere respiration was significantly higher in soybean (0.29 mg C g -1 root h-1) than corn (0.09 mg C g-1 root h-1), which supports previous observations made with regards to slower-growing plants (e.g. soybean) having relatively higher root respiration than faster growing plants. We observed a nonsignificant difference between N2O efflux in the soybean-planted soil and unplanted bulk soil, which is in contrast to the perception that legumes could stimulate more N 2O production from the soil by increasing the N pool through N 2 fixation. While corn had the greatest uptake of fertilizer N, N 2O efflux in corn pots was higher (2.84 mug N pot-1 h-1) than the soybean pots (0.06 mug N pot-1 h-1). In the laboratory setting, denitrification in the microaggregates proceeded at about 4.4 to 39.6 times higher rate than in large macroaggregates, small macroaggregates or the bulk soil, and showed the greatest response to high moisture levels (80% WFPS).

To further the understanding of respiration processes of northern peatlands, the relative importance of each type of belowground respiration was determined at Mer Bleue, a northern peatland located near Ottawa, Ontario, from June to November, 2003. Direct measurements of total, soil organic matter (SOM) and root respiration were made, with rhizosphere respiration determined by residual. Although an aboveground source, determination of live Sphagnum respiration was also attempted in the field. To identify changes in CO2 fluxes with environmental conditions, peat temperature and water table levels were monitored throughout the study period. / SOM respiration was higher than hypothesized at 63% while root and rhizosphere respiration were lower than hypothesized at 21% and 16%, respectively, of total belowground respiration. As the field experiment for determining live Sphagnum respiration was unsuccessful, it was determined by calculation to be 18% of total respiration, slightly higher than hypothesized. Opposite of hypothesized, air temperatures, peat temperatures and water table levels generally had weak and insignificant relationships when linearly regressed with total respiration.

In an effort to contribute to the improvement of Matric Biology education, a survey was conducted in 1996 and 1997 of Matric pupils and first year students at several tertiary institutions, in order to identify those topics which learners found most difficult. Photosynthesis and respiration were among the topics with which Matric Biology learners experienced many conceptual difficulties. The aim of this project was twofold: firstly to identify specific misconceptions students had regarding these topics, and secondly, to develop and evaluate a learning tool that would address these misconceptions. In order to identify the most common specific misconceptions, a quantitative research approach was taken. A three-tiered multiple choice questionnaire was developed, and administered to first year students in the 1998 intakes at MLSultan Technikon and the Biology Department of the University of Natal, Durban. It was also administered to students at the end of their first, second and third years of Cell Biology (University of Natal), Analysis of the questionnaires revealed that students did not understand the complementary relationship between photosynthesis and respiration. Computer-based virtual worlds provide constructivist learning environments, in which visualisation and problem solving in a complex system is possible. It was proposed that use of a virtual world would be an effective means of addressing the misconceptions we identified. A game was developed that presented students with authentic tasks of filling an oxygen cylinder (as an air supply) and a carbon dioxide cylinder (which would later be used to extinguish a fire). In order to do this students were required to solve a series of three puzzles, all of which related to the processes of photosynthesis and respiration. To account for different learning styles, the puzzles were based on three of Gardner's multiple forms of intelligence. Evaluation of the virtual world made use of a combination of quantitative and qualitative research methods. Students' understanding of the processes was measured with the use of the questionnaire. A deeper evaluation of their understanding and affective response to the game was obtained through interviews. It was found that students who had played the game had a clearer understanding of the complementary relationship between photosynthesis and respiration, and understood that respiration in plant cells is a continuous process. Students also showed greater confidence in their grasp of the processes, and reported that playing the game had been an enjoyable way of complementing their traditional lecture material in order to master these concepts. The virtual world was an effective learning tool for addressing the misconceptions students held regarding photosynthesis and respiration. / Thesis (M.Sc.)-University of Natal, Durban, 1998.

[Truncated abstract] A range of biotic and abiotic stresses increase levels of reactive oxygen species (ROS) in plants due to perturbations of chloroplast and mitochondrial metabolism and the generation of ROS in defence responses. The polyunsaturated fatty acids of membrane lipids are susceptible to ROS induced peroxidation yielding various aldehydes, alkenals and hydroxyalkenals including the cytotoxic compound 4-hydroxy- 2-nonenal (HNE). HNE has the potential to cause substantial oxidative damage in cells via its reactivity with sulfhydryl groups of cysteine (Cys) and lipoic acid, the imidazole group of histidine (His) and the ?-amino group of lysine (Lys) protein residues. Analysis of the components of the plant respiratory electron transport chain to HNE revealed a particular susceptibility to inhibition of activity of the alternative oxidase (Aox). Incubation with HNE prevented dimerisation of Aox protein, suggesting that one site of modification was the conserved cysteine residue involved in dimerisation and activation of this enzyme (Cys1). However, a naturally occurring isoform of Aox lacking Cys1 and unable to dimerise, LeAox1b from tomato, was equally sensitive to HNE inhibition, showing that other amino acid residues in Aox also interact with HNE and are likely responsible for inactivation of the enzyme. ... The broader impact of HNE on the whole Arabidopsis mitochondrial proteome was examined by use of various 2-dimensional gel separation techniques coupled with use of HNE-adduct antibodies. 32 proteins involved in a number of mitochondrial functions were found to be susceptible to modification by HNE, including components of the electron transport chain, the TCA cycle, as well as proteins involved amino acid metabolism and stress-responses. Implications of modification of these proteins by HNE are discussed. As HNE is produced in vivo during oxidative stress, the profile of mitochondrial targets of HNE was examined from Arabidopsis cell cultures exposed to various oxidative stress inducers. Menadione and hydrogen peroxide induced oxidative stress throughout the cell, while antimycin A initiated a mitochondrial targeted stress. A differential profile of mitochondrial proteins was observed to be modified by HNE in the various treatments. These results also showed that induction of stress within a whole cell can impact lipid peroxidation within the mitochondria. Overall, this work showed the presence and production of HNE in plant cells, and that HNE, both exogenous and endogenous, has the ability to modify a specific subset of mitochondrial proteins. In several cases this HNE modification was shown to have functional or structural consequences.

No description available.

[Truncated abstract] The mitochondrion is the energy powerhouse that provide energy to many metabolic functions in the form of ATP. Mitochondria in plants are also known to carry out a variety of other important biochemical processes within the cell, including the anaplerotic function of tricarboxylic acid (TCA) cycle, one-carbon metabolism and portions of photorespiration. Dynamics of the mitochondrial proteome in plants underlies fundamental differences in the roles of these organelles under different developmental and environmental conditions. A quantitative comparative proteomic approach was carried out to analyze mitochondria isolated from non-photosynthetic models, cell culture and root, and compared them to mitochondria isolated from photosynthetic shoots. The glycinedependent respiration rate and the protein abundance of the photorespiratory apparatus was found to be higher in shoot than cell culture and root mitochondria. Also, there were major differences in the abundance and/or activities of enzymes in the TCA cycle between the three systems examined. The metabolic pathways that relied on the supply of intermediates from TCA cycle and photorespiration were also altered, namely cysteine, formate and one-carbon metabolism, as well as amino acid metabolism focused on 2-oxoglutarate generation, and branched-chain amino acids degradation. To further provide insight into the extent of mitochondrial heterogeneity in plants, mitochondria isolated from six organ/cell types, leaf, root, cell culture, flower, stem and silique were analyzed. Of the 251 protein spots on a 2D-gel of the mitochondrial soluble/matrix fraction, the abundance of 213 spots were significantly varied between different samples. Identification of these spots revealed a non-redundant set of 79 proteins which were differentially expressed between organ/cell types. ... Importantly, posttranslational modifications played a significant role in the dynamics of the leaf mitochondrial proteome during the diurnal cycle. Overall, these findings indicated that the mitochondrial proteome is dynamic in order to fulfil different functional and physiological requirements in response to organspecific growth and changes in the external environments. These results also indicated that the majority of the changes in the mitochondrial proteome occurred in the matrix and suggested differences in substrate choice/availability in various plant organs and during the diurnal cycle. Further, these analyses demonstrate that, while mitochondrial proteins are regulated transcriptionally by the nucleus, post-transcriptional regulation and/or post-translational modifications play a vital role in modulating the activation state and/or regulation of proteins in key biochemical pathways in plant mitochondria. The integration of proteomics data with respiratory measurements, enzyme assays and transcript datasets will allow the identification of organ-enhanced and/or light/darkresponsive metabolic pathways as well as providing potential targets for reverse genetic approaches for further functional analysis of plant mitochondria.

[Truncated abstract] Mitochondria play an essential role in diverse metabolic pathways in plants. Their primary roles are the oxidation of organic acids via the tricarboxylic acid cycle and the synthesis of ATP coupled to the transfer of electrons from reduced NAD+ to oxygen via the electron transport chain. Plant mitochondria also contain nonphosphorylating bypasses of the respiratory chain, catalysed by the alternative oxidase (AOX), type II NAD(P)H dehydrogenases (NDHs) and uncoupling proteins (UCPs). Each of these components bypasses energy conservation by either circumventing the formation or utilization of the electrochemical proton gradient, and each is encoded by a small gene family in Arabidopsis. It is proposed that the alterative pathways are likely to be involved in balancing cellular redox and energy status and in minimizing the production of ROS generated by over-reduction of basal respiratory chain components. Furthermore the alternative respiratory pathways are thought to play a role in plant responses to stress. In this study a transcriptomic approach was taken to investigate the role of the alternative respiratory pathways in Arabidopsis, with a focus on elucidating the role and regulation of the AOX gene family. Analysis of the expression of the five AOX genes in Arabidopsis over development and in a range of tissues revealed a unique spatiotemporal expression pattern for each gene. Expression profiling using quantitative RT-PCR, MPSS and microarrays detected an abundance of the AOX1a transcript throughout the plant and over development. The expression patterns of other AOX genes provide insight into their putative roles, AOX1b was expressed predominantly in the flower, AOX1d was particularly abundant in senescing leaves and AOX2 expression was only observed in the seed.

Orientador: Paulo Ademar Martins Leal / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-13T09:54:07Z (GMT). No. of bitstreams: 1 CastilloPizarro_CintyaAlejandra_D.pdf: 538268 bytes, checksum: a0775d761ca852aadb1dc74aa8998449 (MD5) Previous issue date: 2009 / Resumo: O morango é produzido e apreciado nas mais variadas regiões do mundo, sendo a espécie de maior expressão econômica entre as pequenas frutas. O Estado de São Paulo é um dos seus maiores produtores no Brasil. De todo o ciclo produtivo do morango, a comercialização tem se mostrado a fase mais complexa e problemática, podendo afetar mais o lucro do que todas as outras etapas de produção. Isso ocorre devido às características do produto, como fragilidade, manuseio inadequado, alta perecibilidade e falta de embalagens e de refrigeração adequados. Por possuir elevado valor comercial, principalmente no mercado in natura, a tecnologia do frio para sua melhor conservação pós-colheita, pode ser utilizado para manter as boas características de qualidade do fruto. Este trabalho teve por objetivo geral definir qual a melhor condição pós-colheita para conservação de morangos quanto a embalagem cumbucas de tereftalato de polietileno (PET) ou em meia cumbuca de tereftalato de polietileno, envoltas por filme de policloreto de vinila (PVC), resfriamento rápido e armazenamento refrigerado, visando seu consumo in natura. Realizaram-se dois experimentos, sendo um para monitoramento da taxa respiratória dos pseudofrutos a 0°C, 5°C, 10°C e 15°C em dois sistemas (sistema de fluxo contínuo e sistema estático). Outro experimento foi feito para avaliar a resposta da fruta expressa pelos parâmetros respiração, sólidos solúveis, pH e acidez titulável, quando estes foram submetidos a processos de resfriamento rápido e armazenagem. As variedades avaliadas foram Camarosa, Sweet Charlie, Dover e Oso Grande. Neste experimento utilizou-se câmaras de armazenamento com regulagem de 0 e 10°C, e os frutos foram embalados em cumbucas PET e PVC. As frutas foram analisadas a cada dois dias, até ficarem impróprias para o consumo. Verificou-se que o melhor método para avaliação da taxa respiratória é o método do sistema de fluxo contínuo, por possuir um fluxo constante durante todo o experimento, assim como melhor reprodutibilidade dos tempos de retenção e da quantificação do CO2 dentro dos frascos. A temperatura 0°C, foi a que possibilitou a maior vida de prateleira dos frutos. Não se observou diferença entre as embalagens PET e PVC no armazenamento a 0°C e a 10°C. Das variedades avaliadas a Sweet Charlie é a que se mostrou mais indicada para consumo in natura, devido suas características fisico-químicas. Enquanto a variedade Camarosa a mais indicada para indústria. / Abstract: The strawberry is cultivated and appreciated in several regions around the world, being the specie with the most economical value among the small fruits. The São Paulo state is one of the biggest producers in Brazil. From all productive cycle of strawberry the commercialization has shown the most complex and problematic phase, and it can affect more the profit than all the others. This happens due to the product characteristics, such as fragility, improper handling, high perishable, inadequate packaging, and use of cold chain. Since strawberry has high commercial value, mainly on in natura maket, the cold chain technology may be used to keep the good characteristics of fruit quality. The objectives were to define which are the best conditions postharvest for the strawberry fruits in terms of packing PET or PVC, precooling and refrigerated storage aiming the consumption in natura. Two experiments were realized, being one to monitoring and evaluating the respiratory rate of the fruits at the temperatures of 0, 5, 10 and 15°C in two different systems: continuous flow system, and static flow system, in BOD's. The other experiment was to evaluate the answer of biochemical parameters (respiration rate, soluble solids, pH and titratable acidity) submitted to the precooling and refrigerated processes using the Camarosa, Sweet Charlie, Dover, and Oso Grande varieties. For this experiment was used chambers at 0 and 10oC, and the fruits had been packed in packs of tereftalate of polyethylene (PET) clam shell type, and packs of tereftalate of polyethylene (PET) wrap with PVC film. Physical-chemical analyses were carried every two days until the fruits got improper for consumption. The experiment show that the optimum method for evaluation respiratory rate is the one using the continuous flow system since presented a constant flow during all the experiments, and allows better accuracy for the retention time and CO2 quantification inside of the bottles. The temperature of 0°C was the one that shows longest fruits shelf life time. There were not differences between packs of tereftalate of polyethylene (PET) clam shell type and packs of tereftalate of polyethylene (PET) wrap with PVC film storaged at 0 and 10°C. Among the varieties, the Sweet Charlie was the most indicated for in natura consumption, due to its physical-chemical characteristics. Meanwhile the variety Camarosa was the most appropriate for industry use. / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola