In order to gain a better understanding of the mechanism of As(V) tolerance in rice, a number of hydroponic tolerance tests have been done on the interaction of As(V) with phosphate (PO<sub>4</sub><sup>3-</sup>), reduced glutathione (GSH) and O<sub>2</sub> supply. The PO<sub>4</sub><sup>3—</sup>As(V) interaction test revealed that increasing PO<sub>4</sub><sup>3-</sup> concentration reduces the toxicity of As(V). Low PO<sub>4</sub><sup>3-</sup> (0.05 mM) showed no protection against As(V) induced root inhibition, but higher PO<sub>4</sub><sup>3-</sup> (0.5 and 5 mM) showed marked protection, suggesting PO<sub>4</sub><sup>3-</sup> derived tolerance is not due to reduced PO<sub>4</sub><sup>3-</sup> transport that has been postulated in other grass species. The glutathione (GSH)-As(V) interaction test revealed a strong effect of GSH, increasing tolerance in rice. The O<sub>2</sub> supply test also revealed a significant effect with enhanced tolerance in rice. Therefore it can be suggested that PO<sub>4</sub><sup>3-</sup>, GSH and air bubbling supply all reduces As(V) toxicity in rice by increasing tolerance. The protection against As(V) provided by GSH and PO<sub>4</sub><sup>3-</sup> were not the same for two rice varieties, Azucena (As sensitive) and Bala (As tolerant). However these tolerance tests cannot explain why Azucena and Bala differ in susceptibility to As(V). Three green house pot experiments revealed that As(V) treatment reduces growth in dose dependent way. Total As concentration in the shoots and grain increases with the increasing concentration of the As(V) treatments. Surprisingly, application of PO<sub>4</sub><sup>3-</sup> does not alter As(V) toxicity. Anaerobic (lowland) soil shows higher shoot As concentration but uptake is lower. Rice genotypes show significant variation in their plant growth, total shoot As concentration and total As uptake which reveal that tolerant genotypes contain higher shoot As. Results of the hydroponics and pot experiments suggested that tolerance of rice is not derived from competition with As(V) at the PO<sub>4</sub><sup>3-</sup> transporters, but rather reflects another, as yet unknown, mechanism.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509206 |
| Date | January 2009 |
| Creators | Nigar, Meher |
| 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=33413 |
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