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- Bohlin, Jan
(författare)
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Enzymes and electron transport in microbial chlorate respiration
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microbial chlorate respiration plays an important role in the turnover of oxochlorates in nature and industrial waste management. This thesis deals with the characterization of the molecular components of chlorate respiration in Ideonella dechloratans. Chlorate respiration utilizes two soluble periplasmic enzymes, chlorate reductase and chlorite dismutase, to convert chlorate to chloride and oxygen. The genes encoding the enzymes participating in the chlorate degradation have been sequenced, and are found in close proximity, forming a gene cluster for chlorate metabolism. This work also includes the successful recombinant expression of three genes from Ideonella dechloratans. Two of the gene products, chlorite dismutase and the C subunit of chlorate reductase, participate in the chlorate respiration. The third gene, which is found close to the gene cluster for chlorate metabolism, encodes a soluble c-type cytochrome. The localization of the gene suggests the corresponding protein as a candidate for a role as electron donor to chlorate reductase. Also, the role of soluble periplasmic c cytochromes of Ideonella dechloratans in chlorate respiration was studied. At least one of the soluble c cytochromes was found capable of serving as electron donor for chlorate reduction. This c cytochrome, and several others, can also donate electrons to a terminal oxidase for subsequent reduction of oxygen, as required for the branched electron flow during chlorate respiration.
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| 2. |
- Kalbina, Irina, 1961-
(författare)
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The molecular mechanisms behind perception and signal transduction of UV-B irradiation in Arabidopsis thaliana
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Elevation of UV-B radiation (280-315 nm), occurring as a result of depletion of the stratospheric ozone, causes a number of physiological and biochemical changes in plants. Damage to the photosynthetic apparatus (including the bleaching of the pigments which trap the sun's energy), to the processes of cell division and growth regulation, and to the composition and replication of genetic material are just some of these changes. The consequences include reduction in growth yield, changes in levels and effects of plant hormones and secondary metabolites, and alteration of interactions between plants and other organisms.This thesis deals with several mechanistic questions related to regulation of responses during UV-B stress in plants. Our results show significant ecotype-specific variability in UV-B response in the model plant Arabidopsis thaliana. Differences at the molecular level (expression of PR-5 and steady-state concentration of H2O2) resulted in statistically significant differences in biomass, rosette size and leaf area. Therefore, it is of great importance to pay attention to the responses of the background ecotypes when for instance studying mechanisms of responses toward ultraviolet-B radiation in mutants.Using a DNA microarray approach, we found a number of novel genes to be differentially expressed under UV-B radiation. Two of the genes (PYROA and MEB5.2) were later used as molecular markers for monitoring of UV-B stress. Promoters of PYROA and MEB5.2 were compared with promoters of genes for the phenylpropanoid pathway. The comparisons indicated only few common elements with the UV-B-regulated promoters of CHS, PAL and CHI. In contrast, the genes identified as being UV-B regulated in this study (MEB5.2, PYROA and UBQ3), completely lacked elements required for the UV-B induction of CHS, indicating that these genes are regulated by different transcription factors. In addition, novel unidentified cis-elements are probably also present upstream of the transcription start.Reverse and forward genetics were used for searching novel genes responsive to UV-B and for examination of proposed candidates of the UV-B signal transduction chain. Screening of more than 2000 T-DNA mutants for differential response to UV-B resulted in the identification of a mutant displaying insensitivity to UV-B induced inhibition of hypocotyl growth. By using the corresponding knock-out mutants, the involvement of NADPH oxidase and MAPK phosphatase 1 in UV-B signalling was demonstrated.For the plant to be able to respond appropriately to UV-B irradiation, UV-B quanta have to be absorbed. There are indirect evidences for the existence of specific UV-B receptor(s), whereas the receptor itself still remains unknown. By the classical approach of action spectroscopy, we undertook an attempt to identify the absorption spectra of the chromophore(s) sensing UV-B radiation in plants. The investigated molecular markers revealed the presence of two potential chromophores absorbing in the UV-B region and peaking at 280-290 and 300 nm, respectively.
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