Growth regulating properties of isoprene and isoprenoid-based essential oils.
Abstract
KEY MESSAGE:
Essential
oils have growth regulating properties comparable to the
well-documented methyl jasmonate and may be involved in localized and/or
airborne plant communication. Aromatic plants employ large amounts of
resources to produce essential oils. Some essential oils are known to
contain compounds with plant growth regulating activities. However, the
potential capacity of essential oils as airborne molecules able to
modulate plant growth/development has remained uninvestigated. Here, we
demonstrate that essential oils from eight taxonomically diverse plants
applied in their airborne state inhibited auxin-induced elongation of
Pisum sativum hypocotyls and Avena sativa coleoptiles. This response was
also observed using five monoterpenes commonly found in essential oils
as well as isoprene, the basic building block of terpenes. Upon transfer
to ambient conditions, A. sativa coleoptiles resumed elongation,
demonstrating an antagonistic relationship rather than toxicity.
Inclusion of essential oils, monoterpenes, or isoprene into the
headspace of culture vessels induced abnormal cellular growth along
hypocotyls of Arabidopsis thaliana. These responses were also elicited
by methyl jasmonate (MeJA); however, where methyl jasmonate inhibited
root growth essential oils did not. Gene expression studies in A.
thaliana also demonstrated differences between the MeJA and isoprenoid
responses. This series of experiments clearly demonstrate that essential
oils and their isoprenoid components interact with endogenous plant
growth regulators when applied directly or as volatile components in the
headspace. The similarities between isoprenoid and MeJA responses
suggest that they may act in plant defence signalling. While further
studies are needed to determine the ecological and evolutionary
significance, the results of this study and the specialized anatomy
associated with aromatic plants suggest that essential oils may act as
airborne signalling molecules.
KEYWORDS:
Airborne signalling; Essential oils; Isoprene; Terpenoids
