Lack of rapid monoterpene turnover in rooted plants: implications for theories of plant chemical defense.

Evidence for the rapid metabolic turnover of leaf monoterpenes is a significant component of theories regarding the evolution and metabolic cost of plant chemical defenses. We re-examined whether monoterpenes are continuously synthesized and lost in intact peppermint plants, and demonstrate that the rapid monoterpene turnover previously observed using detached stems does not occur in intact plants. The apparent artifactual nature of rapid monoterpene turnover in peppermint suggests that a re-evaluation of the rates of metabolic turnover of plant defenses is needed before accurate hypotheses regarding the cost of plant chemical defense can be proposed.