Defense Mechanisms ofConifers1 Differences inConstitutive andWound-Induced Monoterpene Biosynthesis AmongSpecies

Levels ofmonoterpene cyclase activity weredetermined in extracts fromwoundedandunwounded saplings of10conifer species toassess whether oleoresin biosynthesis isinduced by stemwounding. Species ofAbles andPicea, with lowtomoderate levels ofconstitutive monoterpene cyclase activity, exhibited a five- to15-fold increase incyclase activity 7daysafter wounding relative tounwounded controls. Incontrast, species ofgenera suchasPinus, withhighlevels ofconstitutive cyclase activity, didnotsigniflcantly respond towounding byalteration inthelevel ofcyclase activity. Thehighest foldincrease inmonoterpene cyclase activity wasconsistently observed inAbies grandis, and thetime-course ofinduction ofactivity following stemwounding inthisspecies demonstrated a threefold increase at2 days relative tounwounded controls, rising toamaximumincrease in theresponse at9days(greater than10-fold) followed byan apparent decline. Thewoundresponse waslocalized, andboth bark(phloem) andwood(xylem) tissues displayed increased cyclase activity atthewoundsite. Themagnitude oftheincrease incyclase activity wasdependent ontheseverity ofthewound.