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Abstract:
Herbivory is well known to trigger increased emission of volatile organic compounds (VOCs) from
plants, but we know little about the responses of mature trees. We measured the volatiles emitted
by leaves of old-growth black poplar (Populus nigra) trees after experimental damage by gypsy moth
(Lymantria dispar) caterpillars in a floodplain forest, and studied the effect of herbivory on the transcript
abundance of two genes involved in the biosynthesis of VOCs, and the accumulation of defence
phytohormones. Herbivory significantly increased volatile emission from the experimentally damaged
foliage, but not from adjacent undamaged leaves in the damaged branches (i.e., no systemic response).
Methylbutyraldoximes, 4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenol and (E)-β-ocimene,
amongst other compounds, were found to be important in distinguishing the blend of herbivoredamaged
vs. undamaged leaves. Herbivory also increased expression of PnTPS3 (described here for the
first time) and PnCYP79D6-v4 genes at the damaged sites, these genes encode for an (E)-β-ocimene
synthase and a P450 enzyme involved in aldoxime formation, respectively, demonstrating de novo
biosynthesis of the volatiles produced. Herbivore-damaged leaves had significantly higher levels of
jasmonic acid and its conjugate (−)-jasmonic acid-isoleucine. This study shows that mature trees in the
field have a robust response to herbivory, producing induced volatiles at the damaged sites even after
previous natural herbivory and under changing environmental conditions, however, further studies are
needed to establish whether the observed absence of systemic responses is typical of mature poplar trees or if specific conditions are required for their induction.
