Arsenic translocation in rice investigated using radioactive ⁷³As tracer

Background and aims: Excessive accumulation of arsenic (As) in rice (Oryza sativa L.) may pose a health risk to rice consumers. Long-distance transport of As within plant tissues is not well understood. The aim of our study was to evaluate As translocation from roots to shoots and from shoot tissues to rice grain. Methods: At the grain filling stage, ⁷³As-labelled arsenite was fed to roots, cut stems or flag leaves of rice. The root-feeding experiment also included a treatment of steam girdling near the base of panicle to block phloem transport. ⁷³As distribution in different tissues was quantified after 2 or 4 days. Results: In the root-feeding experiment, about 10% of the ⁷³As taken up was distributed to shoots mostly in stems and leaves, with 3. 3% of the shoot ⁷³As found in the grain. Steam girdling decreased grain ⁷³As by 97%. In the stem-feeding experiment, most ⁷³As was retained in the stem with 3. 9% distributed to the grain. In the flag leaf-feeding experiment, 12-15% of ⁷³As was exported to other tissues with 2-3% reaching the grain. Conclusions: As (mainly arsenite) has a relatively low mobility within rice plants. Arsenite was transported to rice grain mainly through the phloem. A small proportion of arsenite fed to flag leaves can be transported to grain.