Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/20/2003
Publication Date: 1/20/2004
Citation: Engelberth, J., Alborn, H.T., Schmelz, E.A., Tumlinson, J.H. 2004. Airborne signals prime plants against insect herbivore attack. Proceedings of the National Academy of Sciences. 101(6):1781-1785. Interpretive Summary: Corn plants emit volatile chemicals shortly after caterpillar attack and these volatiles serve as ecological signals for the attraction of predators and parasitoids, the natural enemies of caterpillars. It has been hypothesized that undamaged plants may also perceive volatiles emitted from the infested neighboring plants as indicators of nearby pests and increased probability of attack. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that wound and insect-induced 6-carbon green leafy volatiles, characteristic of cut grass, stimulate early defense responses in nearby undamaged plants. Corn plants respond to green leafy volatiles by producing a rapid and transient increase in the wound hormone jasmonic acid. Alone, the response to green leafy volatiles initiates only small increases in plant chemical defenses. However, when plants are exposed to green leafy volatiles and secondarily wounded and treated with caterpillar regurgitate, used as a proxy for insect attack, the burst of jasmonic acid and induced volatile defenses are far greater than control plants with no previous green leafy volatile exposure. Importantly, this green leafy volatile sensitization and subsequent response to insect regurgitate is specific and does not occur following simple mechanical damage. Thus, green leafy volatiles specifically prime neighboring plants against impending herbivory by enhancing inducible chemical defense responses triggered during attack and likely play a key role in plant-plant signaling and plant-insect interactions.
Technical Abstract: Green leafy volatiles (GLV), 6-carbon aldehydes, alcohols and esters commonly emitted by plants in response to mechanical damage or herbivory, induced intact, undamaged corn seedlings to rapidly produce jasmonic acid (JA) and emit sesquiterpenes. More importantly, corn seedlings previously exposed to GLV from neighboring plants produced significantly more JA and volatile sesquiterpenes when mechanically damaged and induced with caterpillar regurgitant than seedlings not exposed to GLV. The use of pure synthetic chemicals revealed that Z-3-hexenal, Z-3-hexen-1-ol and Z-3-hexenyl acetate have nearly identical priming activity. Caterpillar-induced nocturnal volatiles, which are enriched in GLV, also exhibited a strong priming effect, inducing production of larger amounts of JA and release of greater quantities of volatile organic compounds (VOC) following caterpillar regurgitant application. In contrast, GLV priming did not affect JA production induced by mechanical wounding alone. Thus, GLV specifically prime neighboring plants against impending herbivory by enhancing inducible chemical defense responses triggered during attack and may play a key role in plant-plant signaling and plant-insect interactions.