Minisymposium 18: Plant defense signaling

Abs # 33005: Green leafy volatiles prime plants against insect herbivor attack

Presenter:	Engelberth, Jürgen , jee11@psu.edu
Authors	Engelberth, Jürgen  (A)   Alborn, Hans T (B)   Schmelz, Eric A (B)   Tumlinson, James H (A)
Affiliations:	(A): Dept. Entomology, Penn State University, University Park, PA (B): CMAVE, ARS, USDA, Gainesville, FL

Green leaf volatiles (GLV), comprising 6-carbon aldehydes, alcohols and esters, are commonly emitted by plants in response to mechanical damage or herbivory. Aerial application of GLV induced intact, undamaged corn seedlings to rapidly produce jasmonic acid (JA) and emit significant amounts of volatile organic compounds (VOC). However, contrary to wounding, no increase in 12-oxo-phytodienoic acid was detected. More importantly, corn seedlings previously exposed to GLV from neighboring plants produced significantly more JA and volatile sesquiterpenes when induced with caterpillar regurgitant (CR) than seedlings not exposed to GLV. The application of pure synthetic chemicals revealed that Z-3-hexenal, Z-3-hexen-1-ol and Z-3-hexenyl acetate as well as the respective E-2-enantiomers have nearly identical priming activity. Further analysis of structure/function relationship revealed that in corn seedlings size (6 carbons) and the position of the double-bond (at position 2 or 3) determine the activity rather than the alpha-beta carbonyl function (Michael-acceptor). Caterpillar-induced nocturnal volatiles, which are enriched in GLV, also induced a transient increase in JA and exhibited a strong priming effect, resulting in the induction of larger amounts of JA and release of greater quantities of VOC following CR application. However, exposure to CR-induced volatiles, which contain only trace amounts of GLV, failed to induce JA in receiver plants. In contrast, GLV priming did not affect JA production induced by mechanical wounding nor by a second application of GLV after 16h. Salicylic acid was also not affected. The susceptibility of corn plants to GLV is strongly affected by age and nutrient supply. In conclusion, GLV specifically prime neighboring plants against impending herbivory by enhancing inducible chemical defense responses triggered during attack. Furthermore, the mechanism of priming may benefit receiver plants by reducing investment in defenses until the onset of actual herbivory. Thus, the effect of GLV is far reaching and influences both directly and indirectly the entire tritrophic complex of plants, insect herbivores and natural enemies of the herbivores.