Studies on the interaction between arsenic (As) and rice varieties which differ in arsenate (As(V)) tolerance

• Main Author: Nigar, Meher
• Published: University of Aberdeen 2009
• Subjects: 571.2; Food contamination : Arsenic : Rice : Agriculture : Water : Soil pollution
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509206

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 (PO₄^3-), reduced glutathione (GSH) and O₂ supply.  The PO₄^3—As(V) interaction test revealed that increasing PO₄^3- concentration reduces the toxicity of As(V).  Low PO₄^3- (0.05 mM) showed no protection against As(V) induced root inhibition, but higher PO₄^3- (0.5 and 5 mM) showed marked protection, suggesting PO₄^3- derived tolerance is not due to reduced PO₄^3- 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 PO₄^3-, GSH and air bubbling supply all reduces As(V) toxicity in rice by increasing tolerance.  The protection against As(V) provided by GSH and PO₄^3- 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 PO₄^3- 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 PO₄^3- transporters, but rather reflects another, as yet unknown, mechanism.