Arsenic uptake is suppressed in a rice mutant defective in silicon uptake

Abstract

AbstractPossible mechanisms of the effects of silicon (Si) on arsenic (As) uptake were explored using a wild‐type rice and its low‐Si mutant (lsi1). Hydroponic experiments were carried out to investigate the effects of internal and external Si on the As accumulation and uptake by rice in excised roots (28 d–old seedlings) and xylem sap (61 d–old plants). The presence of Si significantly decreased the As concentrations in both shoots and roots of the wild type but not in the mutant with 13.3 μM–arsenite or 10/20 μM–arsenate treatments. The Si‐defective mutant rice (lsi1) also showed a significant reduction in arsenite or arsenate uptake. Moreover, As concentrations in xylem sap of the wild type were reduced by 51% with 1 mM Si– and 15 μM–arsenate treatments, while Si had no effect on As concentrations in the xylem sap of the mutant. Arsenic‐species analysis further indicated that the addition of 1 mM Si significantly decreased As(III) concentrations but had little effect on As(V) concentrations in the xylem sap of the wild type with 15 μM–arsenate treatments. These results indicated that external Si‐mediated reduction in arsenite uptake by rice is due to the direct competition between Si and arsenite during uptake. This is because both share the same influx transporter Lsi1. In addition, internal Si‐mediated reduction in arsenite uptake by rice is due to competition of the Si/arsenite efflux transporter Lsi2 during the As(III)‐transportation process. Silicon also inhibited arsenate uptake by rice. It is proposed that this could actually be due not to the inhibition of arsenate uptake per se but rather the inhibition of arsenite transformed from arsenate, either in the external solution or in rice roots.