|Tumlinson Iii, James|
Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2002
Publication Date: 2/10/2003
Citation: SCHMELZ, E.A., ALBORN, H.T., TUMLINSON III, J.H. SYNERGISTIC INTERACTIONS BETWEEN VOLICITIN, JASMONIC ACID AND ETHYLENE MEDIATE INSECT-INDUCED VOLATILE EMISSION IN "ZEA MAYS." PHYSIOLOGIA PLANTARUM. 117:403-412. 2003. Interpretive Summary: Corn plants emit a blend of volatile chemicals shortly after attack by beet armyworm caterpillars. These volatiles are triggered by chemical elicitors present in the caterpillar oral secretions and serve as attractants for predators and parasitoids, the natural enemies of caterpillars. It was hypothesized that volatile emission, triggered by the application of elicitors to the plant leaf surface, must be controlled by the levels of specific plant hormones. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that insect-derived elicitors promote increases in a specific plant hormone, which correlates with volatile emission. However, elicitors alone do not completely mimic the volatile emission stimulated by beat armyworm feeding damage, nor the levels of an additional volatile plant hormone typically increased by insect feeding damage. The combined treatment of plants with insect- derived elicitors and a volatile plant hormone, very closely mimicked the large quantities of plant volatiles emitted during actual insect feeding. An understanding of such interacting plant hormones that regulate insect-induced volatile emission, is critical prior targeting genetic elements to enhance these naturally occurring plant self- defense mechanisms.
Technical Abstract: Plants display differential responses following mechanical damage and insect herbivory. Both caterpillar attack and the application of caterpillar oral secretions (OS) to wounded leaves stimulates volatile emission above damage alone. Volicitin (N-(17-hydroxy linolenoyl)-L- glutamine), present in beet armyworm (BAW, Spodoptera exigua) OS, is a powerful elicitor of volatiles in excised corn seedlings. We consider the mechanistic differences between wounding and insect herbivory by examining the activity of volicitin, changes in jasmonic acid (JA) levels and volatile emission from both intact-plant and excised-leaf bioassays. Compared to mechanical damage alone, volicitin stimulated increases in both JA levels and sesquiterpene volatiles when applied to intact-plants. In a bioassay comparison, excised-leaves were more sensitive and produced far greater volatile responses than intact- plants following applications of both volicitin and JA. Interestingly, volicitin-induced JA levels did not differ between intact and excised bioassays, suggesting a possible interaction of JA with other regulatory signals in excised plants. In an excised-leaf bioassay, volicitin applications (10-500 pmoles) to wounded leaves resulted in dose dependent JA increases and a direct positive relationship between JA and sesquiterpene volatile emission. Insect herbivory is also known to induce ethylene however, volicitin had no effect on ethylene production. When combined with either volicitin or JA, ethylene (at 1 ppm or less) greatly promoted volatile emission. For intact-plants, the combination of wounding, elicitor induced JA and ethylene are atile production.