Insights into the Relationships Between Herbicide Activities, Molecular Structure and Membrane Interaction of Cinnamon and Citronella Essential Oils Components

Since the 50’s, the massive and “environmental naïve” use of synthetic chemistry has
revolutionized the farming community facing the dramatic growth of demography. However, nowadays,
the controversy grows regarding the long-term harmful effects of these products on human health
and the environment. In this context, the use of essential oils (EOs) could be an alternative to chemical
products and a better understanding of theirmode of biological action for new and optimal applications
is of importance. Indeed, if the biocidal effects of some EOs or their components have been at least
partly elucidated at the molecular level, very little is currently known regarding their mechanism of
action as herbicides at themolecular level. Here, we showed that cinnamon and Java citronella essential
oils and some of their main components, i.e., cinnamaldehyde (CIN), citronellal (CitA), and citronellol
(CitO) could act as efficient herbicides when spread on A. thaliana leaves. The individual EO molecules
are small amphiphiles, allowing for them to cross the mesh of cell wall and directly interact with
the plant plasma membrane (PPM), which is one of the potential cellular targets of EOs. Hence,
we investigated and characterized their interaction with biomimetic PPMwhile using an integrative
biophysical approach. If CitO and CitA, maintaining a similar chemical structure, are able to interact
with the model membranes without permeabilizing effect, CIN belonging to the phenylpropanoid
family, is not. We suggested that different mechanisms of action for the two types of molecules
can occur: while the monoterpenes could disturb the lipid organization and/or domain formation,
the phenylpropanoid CIN could interact with membrane receptors.