An international team of researchers from China, Germany, and the United States has made a key finding in the long-standing question about how environmental arsenic ends up in grains of rice. The discovery, published in the January 2016 issue of the journal Nature Plants, may pave the way for approaches that prevent or reduce arsenic uptake, making one of the world’s major food crops safer for human consumption.
Arsenic in rice is a known health risk to populations that rely on the grain in their diets. Arsenic occurs naturally in the environment and is a known human carcinogen that is associated with skin, lung, bladder, kidney, and liver cancer.
Scientists have known for quite some time how arsenic in soil and groundwater is taken up by the roots of the rice plant and transported to its shoots. But until now, how the contaminant finds its way into the grains themselves — and thus, into the human food supply — has been a mystery.
Models tell the story
The team included NIEHS grantees Barry Rosen, Ph.D., an arsenic detoxification expert from Florida International University, and Zihuan Liu, Ph.D., from Oakland University in Michigan. The researchers conducted a series of experiments in three of the classic model organisms used in plant-related research — Arabidopsis thaliana, a small mustard green, Saccharomyces cerevisiae, or baker’s yeast, and oocytes, or female germ cells, of the African clawed frog, Xenopus laevis.
The study showed that two specific transporter proteins, AtINT2 and AtINT4, are responsible for arsenic uptake and accumulation in Arabidopsis seeds. These proteins are known to be responsible for the uptake of inositol, which is important in many metabolic pathways in all organisms. The researchers speculate that knowledge of the pathway of arsenic accumulation in Arabidopsis seeds will shed light on the corresponding mechanism in rice.
Translating to crops
If the study’s findings prove to be applicable to rice, inositol transporters may be candidates for modifications designed to reduce the arsenic content of rice grains. Development of new cultivars that accumulate lower amounts of arsenic in their grain without affecting yield production would represent a significant advance in minimizing the health risks posed by arsenic in rice, the staple food of more than half of the people in the world.
Fred Tyson, Ph.D., a program director for the Division of Extramural Research and Training, elaborated on the wider significance of Rosen’s work. “While much attention has been given to arsenic contamination in drinking water supplies, there currently are no standards for safe arsenic levels in rice,” he said. “However, with the amount of rice consumed around the world, arsenic-contaminated rice could certainly emerge as a global health concern. Dr. Rosen’s research has the potential to provide guidance on how to cultivate rice in ways that significantly reduce the risk of arsenic exposures through rice consumption and has clear translational potential.”
Citation: Duan GL, Hu Y, Schneider S, McDermott J, Chen J, Sauer N, Rosen BP, Daus B, Liu Z, Zhu YG. 2015. Inositol transporters AtINT2 and AtINT4 regulate arsenic accumulation in Arabidopsis seeds. Nature Plants 2:15202
(Ernie Hood is a contract writer in the NIEHS Office of Communications and Public Liaison.)