Plants
under insect herbivore attack have evolved various mechanisms to counteract this threat. Among the measures
plants undertake to survive with the least damage are the recognition of insect-derived elicitors, production
of proteins that block digestion or disrupt intestinal tissue, and the production of defense-related secondary
metabolites, which directly or indirectly affect the herbivore performance. Volatile organic compounds (VOC),
a mixture of volatile secondary metabolites from various pathways, serve as signals not only to attract
predators and parasites of attacking herbivores, but also can be recognized by neighboring plants resulting in
defense-related gene expression. Jasmonic acid (JA) and other lipid-derived compounds (oxylipins), which are
activated by wounding and insect elicitors, represent important signals in this process. In corn (Zea mays),
insect-derived elicitors not only increase the production of oxylipins locally, but also induce JA distal from
the application site within 5-10 min. Green leafy volatiles (GLV), which are rapidly emitted during herbivory,
serve as potent volatile signals for neighboring receiver plants. By inducing specific sections of the
octadecanoid signaling pathway GLV can act as priming signals preparing those plants against impending
herbivory. Structure/function analysis of natural GLV as well as synthetic analogs clearly showed certain
structural requirements, but excluded α,β-unsaturated carbonyls as active centers. A comparison of
gene expression after wounding, wounding with application of crude regurgitant elicitors (CRE), and exposure
to Z-3-hexenyl acetate (Z-3-HAC) further demonstrated the specificity of the GLV signal in plant-plant
communication through selective activation of genes involved in JA biosynthesis. In conclusion, inter-plant
communication via GLV results in an enhanced preparedness specifically directed against insect herbivore
attack mediated by specific activation of distinct parts of the octadecanoid signaling pathway.
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