Function of Essential Oils in Plants
A living plant is a dynamic organism.
There is continuous absorption and transformation of external
substances that allow the plant to thrive and grow.
This process, called assimilation, requires energy, produced
by oxidation reactions within the plant itself.
Of the substances absorbed and produced by the plant, some
are constantly being used and transformed, allowing growth and the
continuation of the metabolic activity of the plant.
Some are products which are stored.
Products like cellulose is deposited in the cell walls,
allowing for the rigid structure of many plants.
Starches are stored as a energy source.
Other substances function, such as alkaloids, anthocyanins,
flavones, essential oils and resins are more difficult to
Many plants emit a considerable amount of organic material,
mostly the carriers of the plant's odor, called essential oils.
Additionally, large amounts of these essential oils are
deposited within the plant itself.
It has been deduced that these essential oils do not provide
an energy source for the plant.
We can assume this, because they remain in the leaves in
plants that lose their leaves. Starch,
or carbohydrate stores, are moved into the stem before the leaves
Therefore, what is the
function of the essential oil? One
idea is that in some cases the oils produce a scent attractive
to certain animals and insects, aiding in pollination.
In other cases the scent is noxious, acting as a repellent;
or irritating, also functioning as a repellent.
Other ideas are that, the oils act as an energy reserve, act
to seal wounds, or as a varnish to prevent evaporation of water.
Attract & Defend!
Many researchers are of
the opinion that the oils are a byproduct of the plant's metabolic
processes, and are of accidental benefit to the plant.
Some, however, refuse to believe that the essential oils are
merely waste products. Lutz
believes that the essential oils can act as an antioxidant or donate
hydrogen in oxidative reactions, especially in the presence of
light. In an experiment
with a fungus, he determined the antioxidant properties of some
essential oil constituents. Previous
work has shown that phenols are excellent hydrogen donors, Lutz
showed that secondary and tertiary alcohols, as well as aldehydes
also performed as antioxidants.
Hydrocarbons were active in the light, but not in the dark.
He also found that primary alcohols, terpene oxides (such as
cineole) and ketones are inactive.
Ultimately, Lutz proposed that the essential oil components
moderate oxidative reactions to protect the plant.
He also feels that it is possible that some of the
constituents may be used as a back-up energy source.
It has been proposed
that essential oils act to keep water in the plant, or to prevent
them from getting too warm. Laboratory
experiments have shown that some essential oils may prevent
transpiration (plant sweating) However, outside the lab it has not
been demonstrated that the essential oil prevent a significant
amount of water loss.
Some essential oil components have toxic effects.
There are some that function similarly to anesthesia on
animal cells. These
qualities are what make it possible to use some essential oils as
bactericides and fungicides. Terpene
derivatives act on certain bacteria.
Others have effects on fibroblasts, and others work on some
types of parasitic worms. Although
some essential oil components work on bacteria and the like, others
have significant effects on higher
functioning organisms. Camphor
and menthol, terpene compounds, are used as circulatory stimulants.
Investigations have determined that these effects seem to be
due to an inhibitory action on the parasympathetic nerve fibers.
Although it is not know how the essential oils work, it is
thought they either disrupt some metabolic systems or interfering or
participating in some reactions.
The oils are transformed in the body for excretion through
the kidney. The
detoxification reactions can consist of esterification, oxidation,
reduction or conjugation. Many
substances are transformed and excreted by the body.
Others may be isolated or walled off, resulting in a sterile
abscess or tumor.
Plants do not have
elaborate detoxification pathways, so will wall off offending
substances. This brings
us back to why many researchers are of the opinion that the
essential oils, resins, alkaloids and other plant compounds are
simply waste products. The
components are now harmful, although they may have been useful in
another form, and have to be isolated in order to prevent damage to
the plant tissue itself.
The Essential Oils, Vol. 1.
Krieger Publishing Co.
All rights reserved 2003, 2004, 2005, 2006. No part of this article may
Rose, Jeanne. 375 Essential
Oils and Hydrosols.
Herbal Library, 415/564-6785. 2000.
be used without prior permission from Jeanne Rose.
© Authors Copyright Jeanne Rose,