The host plant as a factor in the synthesis and secretion of salivary glucose oxidase in larval Helicoverpa zea

We investigated the effect of the host plant on the synthesis and secretion of the elicitor glucose oxidase in the salivary glands of larval Helicoverpa zea. Glucose oxidase catalyses the oxidation of d-glucose to produce d-gluconic acid and hydrogen peroxide. Previous studies have found that the product hydrogen peroxide is primarily responsible for suppressing the wound-inducible defenses of the host plant. Using an antibody specific for glucose oxidase, we determined the effect of the host plant on the rate of secretion of glucose oxidase. Larval H. zea secrete microgram amounts of the enzyme glucose oxidase from their principal salivary glands, the labial glands. Larvae reared on different host plants produce varying amounts of glucose oxidase in their labial glands. We used a tissue printing procedure with our antibody to determine if larvae secrete glucose oxidase directly at the feeding or wound sites. Significant amounts of the enzyme are deposited at the feeding site, although some is deposited outside the feeding margins.