ABSTRACT
Arsenic in paddy soils predominantly occurs in the reduced form-As(III), which is more mobile than As(V). Due to flooding of paddy rice soil and the subsequent decrease of redox potential, the adsorbed As is released. Thus, the rice in the flooded conditions will take up more As than in the aerobic condition, with As(III) the main form of As uptake by the plants. It is transported in the neutral As(OH)3 form through aquaglyceroporins (Meharg & Jardine 2003), and has a similar transporter (Lsi1) with silicon (Si) (Ma et al. 2008). However, As(V) is the main form of As taken up for aerobic rice, with the main route of uptake through the phosphate (P) transporters as a P analogue (Asher & Reay 1979). Abedin et al. (2002) reported that 95% of straw As in rice was inorganic As (Asi), either arsenate or arsenite. Smith et al. (2009) also noted that inorganic As was the predominant form of As in all rice tissues. Therefore, the inorganic As transporters would have a predominant effect on As in grain.
