Selenium and arsenic are important metalloids in the food chain from nutritional and toxicological point of view. These two metalloids are potentially enriched through geogenic processes and anthropogenic activities and they could sometimes co-exist in nature and become available to plants thereby entering the food chain. While selenium is known as an essential element to humans, it could also be toxic. Arsenic on the other hand is a potentially toxic element posing serious health risks to livestock and humans. They have been found to neutralise each other’s effects in animals but their interactions in plants are not well understood. Speciation analysis, which is a set of activities leading to identification and quantification of different forms or species of elements present in an entity, is required for a holistic understanding of the mechanisms and interactions involved in the plants’ metabolism of contaminants and essential elements. Many techniques are currently being used for speciation of selenium and arsenic in plants and they sometimes give contradictory outcomes. The hyphenation of HPLC with MS and synchrotron techniques are the two most commonly used state of the art techniques for speciation of these metalloids. This research therefore sought to access, explore and/ or develop analytical methods appropriate for the speciation of selenium and arsenic in plants. Many selenium and arsenic species have been identified and reported in the literature using well established procedures. The presence of elemental selenium in plants has also been widely reported in plants but to our knowledge this presence has never been experimentally proven and fully quantified. Because this species is non toxic, its proven occurrence in plants will represent a potential detoxification mechanism. Therefore in this study, a method was specifically developed for identification and quantification of elemental selenium. In order to investigate the occurrence of elemental selenium in plants, the newly developed method was applied using Thunbergia alata as a model plant. Arsenic is known to activate the synthesis of PC using glutathione and the complexation of the activating arsenic ions with the synthesised PCs is a well established detoxification mechanism for arsenic. However, very little is known about the role of glutathione and PCs in selenium detoxification. In order to be able to gain better insight into the interaction between selenium and arsenic in plants, the role of glutathione and PCs in selenium metabolism was investigated using Arabidopsis thaliana as a model plant. Sensitivity tests and speciation analysis were carried out on Arabidopsis thaliana WT and the mutants’ one of which is deficient in GSH synthesis and the other deficient in PC synthesis using selenite and arsenate as toxicants. The study revealed that selenium induces the synthesis of glutathione but rather use it as reductant and precursor for transformation and incorporation into peptides and neither GSH nor PCs play any role in selenium detoxification. It was also observed that when selenium and arsenic co-exist there could be competition for PCs between the ions of the metalloids with potentials for increasing arsenic toxicity. Human exposure to inorganic arsenic, a group 1 carcinogen, through Oryza sativa (rice), the staple food for about half the population of the world, has raised serious concerns. Most worrisome are the findings that rice grown in arsenic contaminated areas is characterised by reduced essential amino acids and micronutrients including selenium. A study was therefore conducted to to investigate and understand the interactions between selenium and arsenic in rice. The study confirmed that arsenic could limit the amount of selenium that is taken and translocated to the grains. Selenium was also found to reduce the toxicity of arsenic and most importantly, the study showed that at an appropriate selenium concentration, arsenic uptake and translocation can be reduced.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:577621 |
| Date | January 2013 |
| Creators | Aborode, Fatai Adigun |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=201647 |
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