External Application of Methyl Jasmonate Alters Monoterpene Composition and Induces Resin Duct Production in Engelmann Spruce (Picea engelmannii)

The effects of exogenous application of methyl jasmonate (MeJa), a ubiquitous hormonal elicitor of plant defense, was tested for the ability to upregulate monoterpenes and induce production of traumatic resin ducts in Engelmann spruce (Picea engelmannii). MeJa treatments were applied a single time at one of three concentrations (1-, 10-, and 100-mM) and phloem monoterpene responses were evaluated during the same growing season and one year post-treatment. MeJa application affected monoterpene profiles in a time-specific manner. Total monoterpene concentrations were unaffected by MeJa in the year of application (P = 0.692) but concentrations of several monoterpenes including γ-terpinene, terpinolene, linalool were elevated for trees receiving the 100 mM application, indicating treatment affected monoterpene compositions. Both γ-terpinene (P = 0.008) and terpinolene (P < 0.001) were elevated within one week of application but later declined to control levels, whereas linalool was elevated two weeks after application and remained higher than control for the remainder of the growing season (P < 0.001). Evaluation of traumatic resin duct formation the following year revealed higher frequencies of traumatic resin ducts in growth increments for trees receiving 10- and 100-mM treatments. Occurrence of traumatic resin ducts moderately predicted variation in total monoterpene concentration the year following treatment (P = 0.069). Trees forming resin ducts bisecting between 20 and 90% of the previous year's growth increment had ~ 39% higher mean phloem monoterpene concentrations than trees with fewer ducts or those that were completely occluded by ducts. These results indicate that exogenous MeJa application alters monoterpene profiles shortly following application and may have latent, resin duct-mediated effects on total monoterpene concentrations. Potential ecological impacts are discussed.