| Sumari: | <p>Rice irrigated with arsenic (As) contaminated groundwater can contain concentrations of As in the grain high enough to contribute significantly to dietary intake, leading to increased rates of adverse health effects including cancers of the liver, bladder and kidney.</p>
<p>The exact mechanisms by which As is transported from growth medium to grain are not fully understood. This thesis contains analyses of the distribution of As in the roots of transgenic rice and arabidopsis either defective in, or overexpressing, proteins that are thought to be involved in the transport or detoxification of As in angiosperms (flowering plants), in order to better determine their function.</p>
<p>The plant lines examined were rice mutants defective in Lsi3 transporter (lsi), a low silicon uptake transporter believed to share transport activity with arsenite (As(III)); rice mutants overexpressing PT8 transporter (PT8-Ov), a PHT1 family inorganic orthophosphate (Pi) transporter believed to share transport activity with arsenate (As(V)); arabidopsis mutants defective in phytochelatin (PC) synthase (cad1-3), a protein responsible for forming PCs that are used to chelate and detoxify As(III); and arabidopsis mutants defective in phytochelatin transporters (abcc1-2), that are believed to transport As-PC complexes into vacuoles for storage. All mutants were grown alongside wild type (WT) counterparts.</p>
<p>Analysis of As distributions was carried out by Secondary Ion Mass Spectrometry (SIMS). The data from rice roots revealed strong co-localisation of As and sulphur (S) and high concentrations of these elements in the vacuoles of specific cells in the stele that increased with distance from the root tip and mutation on Lsi3, suggesting Lsi3 plays a role in As efflux.</p>
<p>As concentrations increased in the stele and decreased in the epidermis in PT8-Ov compared to WT supplied with As(V) in the nutrient solution, this could be due to rapid transport and reduction of As(V) to As(III) for detoxification in the stele with PCs.</p>
<p>High concentrations of As and S were also observed in lateral root junctions, in agreement with previous research suggesting that lateral roots play in important role in As uptake.</p>
<p>Within arabidopsis roots high As concentrations were measured in specific cells within the stele and increased with increasing distance from root tip. A higher proportion of As to S compared to WT was observed in cad1-3, suggesting existence of un-chelated As, and there was a significant difference recorded in the distribution of As in abcc1-2 compared to WT, likely due to a lack of available transport mechanisms for As-PC complexes.</p>
<p>Understanding the mechanisms by which As is taken up by rice plants is an important step in developing As mitigation strategies by developing the knowledge required to breed or molecularly engineer low uptake cultivars.</p>
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