"The enzyme is found in insect-resistant strains of corn, and it breaks down proteins and peptides in the insects' gut. It is a unique active defense against herbivory," says Dawn Luthe, professor of plant stress biology at Penn State.
Luthe and researchers at Mississippi State University have since developed several lines of corn resistant to multiple pests, using conventional plant breeding and insect-resistant strains of corn from Antigua.
Researchers have found that when caterpillars fed on the insect-resistant plants, one enzyme -- Mir1-CP or maize insect resistance cysteine protease, in particular --accumulated at the feeding site within an hour of the caterpillar's feeding and continued to accumulate at the site for several days.
"Upon isolation and purification of the enzyme, we found that Mir1-CP binds to chitin, a major component of insects and fungi," says Luthe. "Physiological tests show that caterpillars have impaired nutrient utilization when they eat the enzyme. They just can't convert what they eat into body mass."
Luthe presented the findings at the annual meeting of the American Chemical Society today (March 30) in Atlanta.
With the help of antibodies specific to the enzyme, the researchers were able to determine that Mir1-CP is made in the vascular bundles, or strands of conducting vessels in the stem and leaves of a plant. Luthe thinks that when an insect starts feeding, the enzyme is probably transported to vascular tissue that conducts sugars and other metabolic products upward from the leaves, as well as to the soft tissue found in lea