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You searched for subject:( Sulphur assimilation). Showing records 1 – 2 of 2 total matches.

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Massey University

1. Thomas, Ludivine A. Regulation of sulfur assimilation in onion (Allium cepa L.).

Degree: PhD, Plant Physiology, 2008, Massey University

Onion (Allium cepa L.) is an example of a species that accumulates very high levels of reduced sulfur (S)-containing compounds, particularly in the bulb as alk(en)yl-L-cysteine-sulfoxides (ACSOs) and it is these compounds, or their derivatives, that confers the distinct odour and pungent flavour. In common with higher plants, the S assimilation pathway in onion begins with the activation of uptaken sulfate (SO4 2-) to 5'-adenylylsulfate (APS), a reaction catalysed by ATP sulfurylase (ATPS; EC 2.7.7.4). Then, APS is reduced to sulfide (S2-) in a two-step process catalysed by the enzymes APS reductase (APSR; EC 1.8.4.9) and sulfite reductase (SiR; EC 1.8.7.1). To complete the reductive assimilation pathway, S2- is incorporated into the amino acid skeleton of O-acetylserine (OAS) to form cysteine, and this reaction is catalyzed by OAS (thiol)-lyase (OAS-TL; EC 4.2.99.8). While the regulation of the pathway is quite well defined in the plant model Arabidopsis, much less is known about its regulation in S accumulating species such as onion. The primary aim of this thesis, therefore, was to characterise the enzymes of the S assimilation pathway in onion, with a particular emphasis on ATPS. As part of this charaterisation two genotypes of onion were compared. These comprised a mild genotype, 'Texas Grano 438' (TG) with a lower level of S-containing compounds in the bulb tissues, and 'W202A' (W), a cultivar with a higher level of S containing compounds in the bulb tissues. As well, comparisons were made between seedlings (typically harvested at 7 weeks) and plants at a designated mature stage (at bulbing; typically after 4 months growth), and for plants grown in S-sufficient (S+) media or S-deficicnt (S-) media, as appropriate. In terms of plant growth, S-deprivation generally had a negative influence for both genotypes, with significant reductions in total biomass (measured as fresh weight) for TG at both the seedlings and mature stages. ATPS activity and accumulation were shown to be present in all tissues examined (leaf, root, bulb) as well as the chloroplasts, with highest activity measured in the roots, particularly in seedlings. ATPS activity and accumulation were also compared between the two genotypes (TG and W) with ATPS activity and accumulation higher in W, particularly at the seedling stage. In terms of the influence of S supply, in general higher ATPS activity was measured in chloroplast, leaf and root extracts from plants of both genotypes grown in the S- media, at the seedling stage. In roots of mature plants of both genotypes, a significant increase in activity was measured in response to S-deprivation, while in chloroplasts isolated from mature plants of both genotypes, highest activity was measure in those grown in the S+ media. Finally diurnal variations were observed in chloroplast, leaf and root extracts of both genotypes with a general trend of an increase in ATPS activity and accumulation a few hours after illumination and upon the onset of the dark period. Although a single gene coding for ATPS is…

Subjects/Keywords: Onions; Sulphur assimilation

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APA (6th Edition):

Thomas, L. A. (2008). Regulation of sulfur assimilation in onion (Allium cepa L.). (Doctoral Dissertation). Massey University. Retrieved from http://hdl.handle.net/10179/1396

Chicago Manual of Style (16th Edition):

Thomas, Ludivine A. “Regulation of sulfur assimilation in onion (Allium cepa L.).” 2008. Doctoral Dissertation, Massey University. Accessed August 11, 2020. http://hdl.handle.net/10179/1396.

MLA Handbook (7th Edition):

Thomas, Ludivine A. “Regulation of sulfur assimilation in onion (Allium cepa L.).” 2008. Web. 11 Aug 2020.

Vancouver:

Thomas LA. Regulation of sulfur assimilation in onion (Allium cepa L.). [Internet] [Doctoral dissertation]. Massey University; 2008. [cited 2020 Aug 11]. Available from: http://hdl.handle.net/10179/1396.

Council of Science Editors:

Thomas LA. Regulation of sulfur assimilation in onion (Allium cepa L.). [Doctoral Dissertation]. Massey University; 2008. Available from: http://hdl.handle.net/10179/1396

2. Grégoire, Daniel. Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction .

Degree: 2019, University of Ottawa

Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in aquatic and terrestrial food webs as monomethylmercury (MeHg). Anaerobic microbes are largely responsible for MeHg production, which depends on the bioavailability of inorganic Hg substrates to methylators. Hg redox cycling pathways such as Hg reduction play a key role in determining Hg’s availability in the environment. Although abiotic photochemical Hg reduction typically dominates in oxic surface environments, Hg reduction pathways mediated by photosynthetic and anaerobic microbes are thought to play an important role in anoxic habitats where light is limited and MeHg production occurs. Currently, the physiological mechanisms driving phototrophic and anaerobic Hg reduction remain poorly understood. The main objective of my thesis is to provide mechanistic details on novel anaerobic and phototrophic Hg reduction pathways. I used a combination of physiological, biochemical and trace Hg analytical techniques to study Hg reduction pathways in a variety of anaerobic and photosynthetic bacteria. I demonstrated that Hg redox cycling was directly coupled to anoxygenic photosynthesis in aquatic purple non-sulphur bacteria that reduced HgII when cells incurred a redox imbalance. I discovered that terrestrial fermentative bacteria reduced Hg through pathways that relied on the generation of reduced redox cofactors. I also showed that sulphur assimilation controlled Hg reduction in an anoxygenic phototroph isolated from a rice paddy. In addition, I developed methods to explore cryptic anaerobic Hg redox cycling pathways using Hg stable isotope fractionation. At its core, my thesis underscores the intimate relationship between cell redox state and microbial Hg reduction and suggests a wide diversity of microbes can participate in anaerobic Hg redox cycling.

Subjects/Keywords: Mercury; Redox cycling; Anaerobic bacteria; Photosynthetic bacteria; Heliobacteria; Purple non-sulphur bacteria; Stable isotope fractionation; Sulphur assimilation; Redox homeostasis; Anoxygenic photosynthesis; Bioremediation; Climate change; Fermentation

…coupling points between sulphur assimilation pathways and phototrophic Hg reduction. I chose to… …177 Chapter 6: Sulphur source controls mercury reduction in the anoxygenic phototroph… …191 6.4.3 Reduced sulphur sources favour HgII reduction during anoxygenic photosynthesis… …195 6.4.5 Sulphur cycling and cometabolic Hg transformations in the environment… …112 Figure 4.1: HgII reduction by purple non-sulphur bacteria grown phototrophically or… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Grégoire, D. (2019). Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction . (Thesis). University of Ottawa. Retrieved from http://hdl.handle.net/10393/38722

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Grégoire, Daniel. “Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction .” 2019. Thesis, University of Ottawa. Accessed August 11, 2020. http://hdl.handle.net/10393/38722.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Grégoire, Daniel. “Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction .” 2019. Web. 11 Aug 2020.

Vancouver:

Grégoire D. Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction . [Internet] [Thesis]. University of Ottawa; 2019. [cited 2020 Aug 11]. Available from: http://hdl.handle.net/10393/38722.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Grégoire D. Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction . [Thesis]. University of Ottawa; 2019. Available from: http://hdl.handle.net/10393/38722

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.