INDIVIDUAL VARIATION IN CONSTITUTIVE AND INDUCED MONOTERPENE BIOSYNTHESIS IN GRAND FIR

Variations in the level and distribution of monoterpene synthase activ ities in stem samples of 46 grand fir saplings maintained under contro lled conditions were investigated using sensitive, non-destructive bio analytical techniques that permitted the assessment of constitutive, w ound-induced and ethylene modulated biosynthetic capability of each in dividual. Radiochemically-based in vitro assays, with [1-H-3]geranyl d iphosphate as substrate, revealed considerable quantitative variation in constitutive and induced response levels of total monoterpene synth ase activity, and the analysis of monoterpene distribution generated i n the cell-foe extracts allowed the definition of seven distinct biosy nthetic chemotypes. No correlation was observed between total monoterp ene biosynthetic capacity and chemotype, indicating that both broad qu antitative and qualitative variation in oleoresin monoterpene producti on exists in this native population of grand fir. The implications of these findings for oleoresin-based defense against bark beetle predati on are described. (C) 1997 Elsevier Science Ltd. All rights reserved.