HERBIVORE-INDUCED VOLATILES - THE EMISSION OF ACYCLIC HOMOTERPENES FROM LEAVES OF PHASEOLUS-LUNATUS AND ZEA-MAYS CAN BE TRIGGERED BY A BETA-GLUCOSIDASE AND JASMONIC ACID

The treatment of healthy, undamaged plants of the Lima bean Phaseolus lunatus with solutions of a beta-glucosidase from bitter almonds (at 5 U . ml(-1)) through the petiole results in an enhanced emission of vo latiles to the environment. The compounds are identical with those emi tted in response to infestation with the red spotted spider mite Tetra nychus urticae. Dominant products are the two acyclic homoterpenes 4,8 -dimethyl-1,3E,7-dimethylnonatriene (homoterpene I) and 4,8,12-trimeth yl-1,3E,7E,11-tridecatetraene (homoterpene II) which are of sesquiterp enoid and diterpenoid origin. Therefore, a beta-glucosidase of the her bivore may be considered as the true elicitor for the odor induction. Homoterpene I and most other of the herbivore-induced volatiles can al so be triggered by treatment of the plant with solutions of jasmonic a cid (JA) at 100 nmol . ml(-1) to 10 mu mol . ml(-1). The C-16 homoterp ene II is not significantly induced by JA. The time-course of the enzy matic- and the JA-triggered induction of the volatiles is identical. T he dose-response to JA parallels previous reports on alkaloid inductio n 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 dam age by the beet army worm Spodoptora exigua. In summary, the emission of volatiles after damage by a herbivore resembles the production of p hytoalexins in response to an attacking microorganism and uses similar elicitors and internal transduction pathways.