The stem content of
diterpene resin
acids (
rosin) increases dramatically following wounding of grand fir (Abies grandis) saplings, but the level of
monoterpene olefins (
turpentine) in the stem decreases following injury, in spite of a significant increase in
monoterpene cyclase (synthase) activity. However, this observation was explained when rapid evaporative losses of the volatile
monoterpenes from the
wound site was demonstrated by trapping experiments, a finding consistent with a role of
turpentine as a
solvent for the mobilization and deposition of
rosin to seal the injury. Mature forest trees responded to stem wounding by the enhancement of
monoterpene cyclization capacity in a manner similar to 2-year-old grand fir saplings raised in the greenhouse. Light and water stresses greatly reduced the constitutive level of
monoterpene cyclase activity and abolished the
wound-induced response. The diminution in
monoterpene biosynthetic capacity was correlated with a dramatic decrease in cyclase
protein as demonstrated by immunoblotting. Relief of stress conditions resulted in the restoration of cyclase activity (both constitutive and
wound induced) to control levels. The results of these experiments indicate that grand fir saplings are a suitable model for studies of the regulation of defensive oleoresinosis in conifers.