| Popis: |
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 (PO43-), reduced glutathione (GSH) and O2 supply. The PO43—As(V) interaction test revealed that increasing PO43- concentration reduces the toxicity of As(V). Low PO43- (0.05 mM) showed no protection against As(V) induced root inhibition, but higher PO43- (0.5 and 5 mM) showed marked protection, suggesting PO43- derived tolerance is not due to reduced PO43- 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 O2 supply test also revealed a significant effect with enhanced tolerance in rice. Therefore it can be suggested that PO43-, GSH and air bubbling supply all reduces As(V) toxicity in rice by increasing tolerance. The protection against As(V) provided by GSH and PO43- 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 PO43- 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 PO43- transporters, but rather reflects another, as yet unknown, mechanism. |
