Patterns of induced and constitutive monoterpene production in conifer needles in relation to insect herbivory

Abstract

Studies were conducted to determine whether herbivore-induced synthesis of monoterpenes occurs in the needles of ponderosa pine (Pinus ponderosa Lawson), lodgepole pine (P. contorta Douglas var. latifolia Engelmann), white fir (Abies concolor Lindl. and Gordon) and Engelmann spruce [Picea engelmanii (Parry) Engelm.]. In the needles of all species except Engelmann spruce, simulated herbivory significantly induced the activity of monoterpene cyclases 4-8 days after wounding. In ponderosa pine, real herbivory by last-instar tiger moth larvae (Halisdota ingens Hy. Edwards: Lepidoptera) induced a significantly larger response (4.5-fold increase in monoterpene cyclase activity) than did simulated herbivory (2.5-fold increase). To our knowledge, this is the first report of herbivore-induced increases in monoterpene synthesis in needle tissue. Despite this increase in monoterpene synthesis, we observed no significant increase in total monoterpene pool size in wounded needles compared to controls. Large increases in the rate of monoterpene volatilization were observed in response to wounding. We conclude that the volatile losses caused by tissue damage compensate for herbivore-induced monoterpene synthesis, resulting in no change in pool size. Tiger moth larvae consume ponderosa pine needles in a pattern that begins at the tip and proceeds downward to midway along the needle, at which point they move to an undamaged needle. Constitutive monoterpene concentrations and monoterpene cyclase activities were highest in the lower half of ponderosa pine needles. The monoterpene profile also differed between the upper and lower needle halves, the lower half possessing an additional one to four monoterpene forms. We propose that the increasing gradient in monoterpene concentrations and number of monoterpenes along the needle from tip to base deters feeding beyond the midway point and provides time for the induction of increased cyclase activity and production of new monoterpenes. The induction of new monoterpene synthesis may have a role in replacing monoterpenes lost through damage-induced volatilization and preventing extreme compromise of the constitutive defense system.

Light dependency of VOC emissions from selected Mediterranean plant species

“…The common method of using abscissic acid to control G s was not used here, because this method requires excision of the shoot and emissions of VOCs are known to respond to stress (e.g. Litvak and Monson, 1998). The use of coloured light to control G s was also considered unsuitable in view of the lack of knowledge of the effect of light on monoterpene emissions.…”

Journal of Range Management, Volume 53, Number 6 (November 2000)

“…Losses of volatile compounds from green pine needles as they weather may result in flavors that are somewhat dissimilar. Further, weathered needles may initially be more acceptable to cattle than are fresh, green needles (Litvak and Monson 1998). Some toxic plants, like tall larkspur (Delphinium barb e y i), are not acceptable to cattle when immature (Pfister et al 1997) but with changes in phenology become more acceptable, presumably because of flavor changes.…”

“…Anecdotal accounts suggest that cattle readily eat needles from slash piles, and this study confirmed that green, but drying, needles are readily accepted by cattle. Again, this may have been due to losses of volatile compounds from drying needles compared to needles on live trees (Litvak and Monson 1998 ). Thus, livestock producers with pine tree-infested pastures must exercise caution to keep pregnant cattle away from slash piles or fallen trees.…”

Wood production, wood technology, and biotechnological impacts

“…genetic, biochemical) and external (e.g. interaction with fungi and insects) factors that affect the presence (Litvak & Monson 1998) and emission of different VOCs by trees and other plants (Apel et al 1999, Peñuelas & Llusià 2001) which are not yet covered by known algorithms.…”