Rice plant variety defies toxic arsenic



Rice plants easily absorb the toxic heavy metal arsenic through their roots, which means that rice is often considered to be highly polluted. But a certain variety of rice can defy the toxin, as studies have now shown. According to this, the plant has mutated in such a way that the grains of the plant contain very little arsenic, even though they grow in contaminated fields. In addition, their rice grains contain a lot of selenium.

The heavy metal arsenic occurs naturally in the earth’s crust and is also released through mining and the use of fossil fuels. In this way it reaches the soil and the groundwater more and is absorbed by plants. Cereal crops such as rice in particular absorb a lot of arsenic. Since the heavy metal is poisonous, fewer grains of rice are formed and there are crop failures. In addition, the absorption of arsenic leads to the potentially carcinogenic substance entering our food chain. Frequent consumption of rice products is therefore not recommended.

Which plants are less polluted?

Above all, rice plants in Asian cultivation areas, in which, among other things, arsenic-containing agents are fertilized, contain increasing amounts of arsenic. That is why researchers working with Sheng-Kai Sun from the Agricultural University of Nanjing in China have now looked for plant variants that absorb less arsenic. To do this, they planted over 4,000 different varieties of the species Oryza sativa in fields with arsenic-containing water and observed their growth. They then measured the arsenic content of the rice grains of the various plants as well as the proportion of other nutrients and marked the arsenic in order to be able to document its accumulation in the plants more precisely. They also compared the root growth and the number of grains of rice in the plants. Finally, Sun and his colleagues examined the genome of the crop variants.

In fact, one of the plant variants examined proved to be tolerant of the poisonous semimetal. In the field trial, their rice grains contained a third less arsenic than the grains of conventional varieties that were also exposed to the arsenic-containing water. The researchers also found a 75 percent increase in the proportion of the trace element selenium. With sufficient light, the roots of this plant variant grew at least as much as those of the other rice plants, some even up to twice longer. In addition, the researchers obtained a grain yield that was just as large with this plant variant as with common high-yield rice plants.

Point mutation changes uptake

During the genome investigation of the rice plants, Sun and his team discovered the cause of the reduced arsenic uptake of the rice variety. They found that a single base pair in the genome of this variant has mutated. The so-called “arsenite-tolerant mutant 1” (astol1) ensures that the function of a protein changes. “This protein is part of a sensor complex and controls the formation of the amino acid cysteine, which is an important raw material for the production of phytochelatins,” explains RĂ¼diger Hell from Heidelberg University. “These substances have a detoxifying effect and are produced by plants as a reaction to pollutants in order to neutralize them.”

The neutralized arsenic is stored in the roots of the plant without reaching the edible rice grains. This means that it cannot be dangerous to humans, according to the researchers. In addition, the mutation ensures that a certain enzyme in this complex, serine acetyltransferase, increases the uptake of sulfate and the trace element selenium. “In addition, the mutation significantly increased the selenium content in the rice grain, an essential micronutrient that up to a billion people around the world ingest inadequately with their food,” add the scientists.

This makes the rice grains twice as beneficial, so that this plant could be particularly suitable for agricultural use, according to the research team. “In the future, rice plants like astol1 could be used in arsenic-contaminated regions to feed the population and at the same time make a contribution to combating diet-related selenium deficiency,” Sun speculates.

Source: Heidelberg University, Article: Nature Communications, doi: 10.1038 / s41467-021-21282-5

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