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.