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Radioactive tracer shows corn roots fight pest

Scientists have used radioisotopes to uncover the mechanisms corn plants use to combat a major pest, the western corn rootworm.

“The western corn rootworm is a voracious pest,” says Richard Ferrieri, a research professor in the University of Missouri Interdisciplinary Plant Group, and an investigator at the University of Missouri Research Reactor.

“Rootworm larvae hatch in the soil during late spring and immediately begin feeding on the crop’s root system. Mild damage to the root system can hinder water and nutrient uptake, threatening plant fitness, while more severe damage can result in the plant falling over.”

Hybrid corn releases toxin that kills hungry worms

Breeding corn that can fight these pests is a promising alternative. Ferrieri and colleagues used radioisotopes to trace essential nutrients and hormones as they moved through live corn plants. In a series of tests, the team injected radioisotope tracers in healthy and rootworm-infested corn plants.

“For some time, we’ve known that auxin, a powerful plant hormone, is involved in stimulating new root growth,” Ferrieri says. “Our target was to follow auxin’s biosynthesis and movement in both healthy and stressed plants and determine how it contributes to this process.”

corn plant getting radioactive tracer
Researchers injected radioisotope tracers in healthy and rootworm-infested corn plants. (Credit: Richard Ferrieri)

By tagging auxin with a radioactive tracer, the researchers were able to use a medical diagnostic imaging tool call positron emission tomography, or PET imaging, to “watch” the movement of auxin in living plant roots in real time.

Similarly, they attached a radioactive tracer to an amino acid called glutamine that is important in controlling auxin chemistry, and observed the pathways the corn plants used to transport glutamine and how it influenced auxin biosynthesis.

The researchers found that auxin is tightly regulated at the root tissue level where rootworms are feeding. The study also revealed that auxin biosynthesis is vital to root regrowth and involves highly specific biochemical pathways that are influenced by the rootworm and triggered by glutamine metabolism.

PET scan of corn plant
By tagging auxin with a radioactive tracer, the researchers could use PET imaging to “watch” the movement of auxin in living plant roots in real time. (Credit: Richard Ferrieri)

“This work has revealed several new insights about root regrowth in crops that can fend off a rootworm attack,” Ferrieri says. “Our observations suggest that improving glutamine utilization could be a good place to start for crop breeding programs or for engineering rootworm-resistant corn for a growing global population.”

According to estimates, the current global population is more than 7.4 billion people and is growing at a rate of 88 million people per year. Developing corn varieties that are resistant to pests is vital to sustain the estimated 9 billion global population by 2050.

The study appears in the journal Plant Physiology.

Source: University of Missouri

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