Individual variation in constitutive and induced monoterpene biosynthesis in grand fir

Variations in the level and distribution of monoterpene synthase activities in stem samples of 46 grand fir saplings maintained under controlled conditions were investigated using sensitive, non-destructive bioanalytical techniques that permitted the assessment of constitutive, wound-induced and ethylene modulated biosynthetic capability of each individual. Radiochemically-based in vitro assays, with [1-H-3]geranyl diphosphate as substrate, revealed considerable quantitative variation in constitutive and induced response levels of total monoterpene synthase activity, and the analysis of monoterpene distribution generated in the cell-foe extracts allowed the definition of seven distinct biosynthetic chemotypes. No correlation was observed between total monoterpene biosynthetic capacity and chemotype, indicating that both broad quantitative and qualitative variation in oleoresin monoterpene production exists in this native population of grand fir. The implications of these findings for oleoresin-based defense against bark beetle predation are described. (C) 1997 Elsevier Science Ltd. All rights reserved.