Herbivore‐induced volatiles: The emission of acyclic homoterpenes from leaves of Phaseolus lunatus and Zea mays can be triggered by a β‐glucosidase and jasmonic acid

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Abstract
The treatment of healthy, undamaged plants of the Lima bean Phaseolus lunatus with solutions of a β-glucosidase from bitter almonds (at 5 U·ml−1) through the petiole results in an enhanced emission of volatiles to the environment. The compounds are identical with those emitted in response to infestation with the red spotted spider mite Tetranychus urticae. Dominant products are the two acyclic homoterpenes 4,8-dimethyl-1,3E,7-dimethylnonatriene (homoterpene I) and 4,8,12-trimethyl-1,3E,7E,11-tridecatetraene (homoterpene II) which are of sesquiterpenoid and diterpenoid origin. Therefore, a β-glucosidase of the herbivore may be considered as the true elicitor for the odor induction. Homoterpene I and most other of the herbivore-induced volatiles can also be triggered by treatment of the plant with solutions of jasmonic acid (JA) at 100 nmol·ml−1 to 10 μmol·ml−1. The C16 homoterpene II is not significantly induced by JA. The time—course of the enzymatic- and the JA-triggered induction of the volatiles is identical. The dose—response to JA parallels previous reports on alkaloid induction in cell cultures. In corn plants (Zea mays) JA triggers the emission of all volatiles which are known to be emitted in response to the damage by the beet army worm Spodoptora exigua. In summary, the emission of volatiles after damage by a herbivore resembles the production of phytoalexins in response to an attacking microorganism and uses similar elicitors and internal transduction pathways.