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Aaron Smith demonstrates the technique for growing rice indoors to study how the plants absorb arsenic. Photo by Bruce Schultz
Aaron Smith, an LSU molecular biologist, is working to find out which genes determine how a rice plant absorbs arsenic from the soil.
In recent years, attention has been focused on arsenic levels in several foods, including rice.
“We’re already confident that there is a genetic component to arsenic accumulation in rice,” said Smith, who began working on the arsenic project with LSU AgCenter rice breeder Steve Linscombe in 2014.
Some varieties appear to have more capacity to take up arsenic than others.
“What we are trying to learn is which genes are responsible for those differences,” Smith said.
Previous work has identified some of the pathways used in plant roots to absorb arsenic, so Smith wants to find out how much arsenic accumulates higher up in the plant and ultimately into the grain.
Plants absorb arsenic the same way they take up nutrients such as phosphorus and silicon, he said.
“We’d like to find a rice variety that has undetectable or very low levels of arsenic in the grain,” Smith said.
He wants to learn what biochemical processes and pathways lead to arsenic getting into the seeds.
Perhaps in some varieties, the roots absorb arsenic without moving the element higher into the plant. But he said completely blocking arsenic uptake is challenging because that also would prevent a plant from absorbing important nutrients such as silicon and phosphorus.
Smith said exposure to arsenic can result in a phenomenon known as straighthead that results in panicles with incomplete grain filling. Arsenic can trigger straighthead, but the condition is also caused by other factors, he said
Linscombe has a nursery to test for tolerance of rice to straighthead, and Smith plans to take plant tissues from that source and analyze the material for arsenic content.
Smith also is growing rice plants indoors in a hydroponic lab where the seedlings are fed small amounts of arsenic, in the parts-per-billion range, along with required nutrients. The plants’ roots will be analyzed for arsenic content.
To find the genes responsible for arsenic uptake, the genetic makeup of plants with relatively high amounts of arsenic will be compared to plants with low amounts of arsenic. He said the SuperMike-II supercomputer at LSU will be used to analyze those genetic sequences.
Smith also has a National Science Foundation grant to study how phosphorus is taken up by rice plants, and what he learns from that project could be used in the arsenic work.
Once genetic markers are found for arsenic uptake, they can be used to screen lines for the development of a rice variety with reduced arsenic levels.
