By Tan Ee Lyn

HONG KONG, July 15 (Reuters) - Scientists in Japan may have discovered why rice absorbs so much arsenic from the soil, paving the way for fresh efforts to block the potentially harmful element from Asia's staple food.

In the Proceedings of the National Academy of Sciences, they said they had identified two proteins in rice plants that appeared to transport arsenic from the soil to the grain.

Using mutant paddy that did not have these two proteins, the experts found sharply reduced levels of arsenic.

"We used mutant paddy (in which) these two transporters were knocked out and we saw decreased arsenite in both the stalk and rice grain," said Ma Jianfeng at Okayama University's Research Institute for Bioresources.

Arsenic occurs naturally in the environment and was used in small amounts in the past to cure diseases like syphilis. But prolonged exposure to arsenic, like in drinking water, has been linked to cancers of the lung, bladder and skin, numbness, cardiovascular disease and diabetes.

Arsenic poisoning is especially serious in places such as Bangladesh and West Bengal in India, where arsenic-contaminated groundwater is used for irrigating rice crops, resulting in arsenic accumulation in soils and grain.

However, Ma's team found the absence of the two transporter proteins reduced the absorption of silicon from the soil. Silicon occurs naturally and is important for the growth and productivity of rice plants. It also protects rice from pests and disease.

"Silicon concentration was also decreased. So in future we have to try to change the selectivity, to allow silicon to be transported but not arsenic. That's what we have to do in future," Ma told Reuters in a telephone interview.

Ma also recommended that more silicon fertilisers be used.

"Silicon and arsenic use the same transporters ... (using) more silicon fertilisers in paddy fields (will result in) more silicon uptake and less arsenic," Ma said.

A Scandinavian team of researchers recently found that a gene that helps plants fight off fungal infections appears to allow plant cells to absorb arsenite.

That team hopes that their findings could one day lead to genetically engineered crops that allow rice, for example, to accumulate silicon but not arsenic. (Editing by Jeremy Laurence)

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