Teses e Dissertações
URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/1
Teses e dissertações defendidas no contexto dos programas de pós graduação da Instituição.
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Item Role of mitochondrial thioredoxin for redox regulation in the metabolism of Arabidopsis Thaliana(Universidade Federal de Viçosa, 2017-03-16) Pereira, Paula da Fonseca; Nesi, Adriano Nunes; http://lattes.cnpq.br/6419216674405263Redox-dependent changes substantially influence the functional activity of several proteins and participate in the regulation of the most vital cellular processes. Accordingly, thioredoxins (Trxs), small proteins containing a redox active disulfide group within its catalytic domain, have a fundamental role in the regulation of the redox environment of the cell. In plants, Trxs were early identified as mediators between light-driven electron transport and dark carbohydrate metabolism in chloroplasts. In other cell compartments than plastids, and in particular mitochondria, a growing body of information concerning Trx redox regulation has been obtained with the advent of proteomics and mass spectrometry-based techniques. Extraplastidial Trx system is comprised of two highly similar isoforms of NADPH-dependent Trx reductase, A and B, that are encoded by two distinct genes in Arabidopsis, whose gene products are denominated NTRA and NTRB and are both target to cytosol and mitochondria. The extraplastidial Trx system is also composed of several Trx h (in the cytoplasm) or Trx h and o in mitochondria which are, in turn, reduced by NTRA and NTRB. Previous studies showed that, in contrast to ntra and ntrb single knockout mutants, which show no visible phenotypic modifications under normal conditions, the double ntra ntrb mutant exhibit major modification differences. Previous studies have provided a significant contribution to our understanding of the TRX system in plants; however, the metabolic impact of this system has not been comprehensively evaluated. In order to gain more insight into the physiological and metabolic function of TRX system, the present study aimed to investigate the functional significance of Trx in cytosol and mitochondria by using an extensive steady state metabolic characterization of T-DNA insertional lines in Arabidopsis thaliana. That being said, here we focused on the investigation of the functional roles of TRXs in response to stress conditions and how Trxs and the regulated pathways interact to adjust to different cellular and metabolic requirements under normal growth conditions or following stress. In brief, the results presented here provided several novel findings and generated, at least preliminary, mechanistic interpretation of the impact of redox regulation on plant growth and carbon central metabolism. First, we characterized ntra ntrb double knockout mutant and two lines of the mitochondrial AtTRX-o1 subjected to multiple drought episodes. Our results indicate that Trx mutant plants are able to better cope with drought stress, which is probably linked with a lower energetic expenditure that would allow a faster recover in Trx mutants. In addition, we demonstrated the existence of a drought memory in plants by examining differential acclimative mechanisms associated with drought tolerance in Trx mutants of the mitochondrial Trx pathway in Arabidopsis. Moreover, it seems likely that this differential acclimation involves the participation a set of metabolic changes as well as redox poise alteration following recovery. The main results indicate that prior drought exposure is able to affect the subsequent response, indicating the occurrence of stress memory in drought stressed Arabidopsis plants. In addition, by evaluating physiological and metabolic responses of ntra ntrb and trxo1 mutants following high CO 2 enrichment and by the characterization of mitochondrial trxh2 knockout mutants, we demonstrate several evidences suggesting the importance of redox regulation by mitochondrial Trxs on stomatal function. Collectively, our data suggest a significant modulation of stomatal function by organic acids at high CO 2 in Trx mutants and, at the same time, they demonstrate that elevated CO 2 partly restored the metabolic response, including the intermediates of the TCA cycle, in Trx mutants. Overall, the results obtained are discussed both in terms of the importance of Trx for redox regulation in plant cell metabolism and with regard to the contribution that it plays in terms of total cellular homeostasis. The results discussed here not only provide important insight into the role of mitochondrial Trx system on the TCA cycle but also present a roadmap by which the role of Trx in the regulation of other key metabolic reactions of the mitochondria.Item Functional characterization of the mitochondrial adenine nucleotide transporter (ADNT1) in Arabidopsis thaliana under dark-induced senescence(Universidade Federal de Viçosa, 2013-02-28) Pereira, Paula da Fonseca; Nesi, Adriano Nunes; http://lattes.cnpq.br/6419216674405263Unlike other ADP/ATP carriers, ADNT1 is the only one that mediates an antiport of ATP, AMP, and, to a lesser extent, ADP and the corresponding deoxyadenine nucleotides. Previous work observed that ADNT1 expression is much stronger in root tips and senescing tissues. Considering the high expression of ADNT1 in senescing tissues, we have investigated the role of ADNT1 during the process of dark-induced senescence. Under these conditions, Arabidopsis thaliana mutants deficient in the expression of ADNT1 transporter displayed a similar, yet milder, early onset of senescence as evidenced both by the visual phenotype of plants following growth in extended periods of darkness and the loss of chlorophyll and photosynthetic competence. The extended dark treatment led in general to a more rapidly decline in the mutants than in the wild type in the levels of sucrose and protein. By contrast, the levels of total amino acids and TCA cycle intermediates malate, fumarate and isocitrate generally increased significantly in the mutants at the end of dark treatment. The NADH/NAD + and NADPH/NADP+ ratios also increased in mutants in comparison to the wild type with progression of the darkness. Additionally, the mutant plants exhibited symptoms of early senescence in comparison to the wild type even under optimal conditions. Altogether the data obtained demonstrate that ADNT1 is not functionally redundant to the previously characterized ADP/ATP carriers, especially during carbon starvation and reinforce the potential function for ADNT1 in the provision of energy which is required to support growth in heterotrophic plant tissues.