|Tumlinson Iii, James|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2002
Publication Date: 9/11/2002
Citation: Schmelz, E.A., Alborn, H.T., Banchio, E., Tumlinson Iii, J.H. 2002. Quantitative relationships between induced jasmonic acid levels and volatile emission in zea mays during spodoptera exigua herbivory. Planta. 216:665-673. Interpretive Summary: Shortly after corn plants are attacked by beat armyworm caterpillars they emit a blend of volatile chemicals that serve as attractants for predators and parasitoids, the natural enemies of caterpillars. Volatile emission, stimulated by caterpillar feeding damage, was hypothesized to be regulated by the levels of specific plant wound hormones. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that during insect feeding damage, levels of a particular plant wound hormone directly correspond to the quantities of plant volatiles emitted. In the abscence of caterpillars, application of this purified hormone to the leaf surface also leads in increases in volatile emission. The regulation of, and plant sensitivity to, this wound hormone will directly effect the amount of plant volatiles emitted and thus the plants ability to attract of natural enemies over long distances. In collaboration with traditional breeding and genetic engineering, an enhancement of insect stimulated wound hormone production would increase volatile production and thus enable plants to defend themselves more effectively against insect pests.
Technical Abstract: Corn seedlings have been used extensively to examine insect-induced volatile production and the activity of insect-derived elicitors present in caterpillar oral secretions. Jasmonic acid (JA) has long been hypothesized to be an important regulator of insect induced volatile emission; however our current understanding is based primarily on pharmacological studies. Using beet armyworm caterpillars (BAW: Spodoptera exigua) and intact corn seedlings, we examine this hypothesis by measuring both the time course of insect-induced JA levels and the relationship between JA and volatile emission (including sesquiterpenes, indole and ethylene). In the Morning time-course trial, BAW herbivory resulted in increased JA levels, sesquiterpene and indole emission within the first 4 hr. After 8-12 hrs of herbivory, levels of JA, ethylene, sesquiterpenes, and indole were all strongly induced. In Evening time-course trial, nocturnal herbivory first increased JA levels within 6hr, then induced sesquiterpene and indole emission within 11 hours. In the following photoperiod, JA levels and indole emission plateaued, while sesquiterpene emission and ethylene production continued to increase relative to control plants. By varying the intensity of the BAW herbivory, we demonstrate that strong positive relationships exist between the resulting variation in in insect-induced JA levels and volatile emissions. In the absence of herbivory, mechanical damage, JA and volicitin (an insect derived elicitor) all promote volatile emission; however, volicitin induced volatiles are transient while JA induced a more sustained over time. Taken as a whole, our results strongly support a role for JA in intact corn plants.