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A variety of plants respond to attacks from herbivorous pests by synthesizing substances that deter their visitors from further feasting. Now scientists have discovered a new, fast-acting form of self-defense that some strains of corn use to defend against caterpillars attempting to feed on them. The findings, published online this week by the Proceedings of the National Academy of Sciences, could help researchers better protect corn crops from hungry invaders.
Tibor Pechan of Mississippi State University and colleagues studied a strain of corn resistant to attacks from fall armyworm caterpillars (see image) and southwestern corn borers in order to determine its mechanism of defense. The key, they determined, was the production of a unique enzyme known as 33-kDa, which the plants manufacture within an hour of an attack. Caterpillars reared on corn that produces the enzyme grew to only half the size of caterpillars fed strains that don't manufacture 33-kDa. Using electron microscopy, the researchers studied the affected insects and determined that the enzyme interferes with the membrane that lines their stomachs. According to the report, the membrane is "the caterpillar's first line of defense" so the disruption compromises the caterpillar's ability to absorb nutrients and renders it more susceptible to toxins and pathogens. In a second test, the scientists genetically engineered plants to express excess 33-kDa and observed results that were even more pronounced. Caterpillars raised on the GM plants were only a quarter of the size of their counterparts raised on regular corn. Because 33-kDa has no effect on the human digestive system, the researchers posit that the approach "may have applications in agricultural biotechnology."