Aromatic Compounds in Plants: Functions Beyond Adding Deliciousness

7 Dec

I purchased some oregano at the market the other day. As its persisting, pleasant smell provided a lot of pleasure on my way home, I found myself asking: what is this deliciousness? Where does it come from?

The characteristic properties of many herbs and spices can be ascribed to essential oils, or aromatic compounds. These compounds are often distinct for certain plants – for instance, carvacrol in oregano – and not only provide cooks with great tools for  enhancing foods, but also serve significant functions for the plants themselves.

Aromatic chemicals have proven to provide efficient protection against insects and other herbivores, and many studies suggest that compounds such as carvacrol have considerable effects on the structural and functional properties of cytoplasmatic membrane of microbes, and thus serve protect the plant against harmful microorganisms.

The defensive aroma chemicals, however, can also have disruptive effects on a plant’s own cells, so plants take care to isolate them from their inner workings. Herbs and spices stockpile their aroma chemicals in specialized oil-storage cells, in glands on the surface of leaves, or in channels that open up between cells. Generally, they are found in peltate glandular trichomes on the aerial parts of the plant. These glandular trichomes consist of highly specialized secretory cells in which the components of the essential oil are synthesized and subsequently accumulate in a subcuticular storage cavity. Plant essential oil biosynthesis is often restricted to special morphological structures like idoblasts (plant cells containing non-living substances), ducts or trichomes that can store these lipophilic compounds in high concentrations. In other words, only a relatively small amount of plant cells produce and store the essential oils.

While it is known what cells may produce these compounds, the question of intracellular localization and organization is less clear. As the aromatic compounds are not directly essential for the basic processes of growth and development, they are classified as secondary metabolites. Different metabolic pathways may be responsible for the biosynthesis, and many different kinds of chemicals fall under the category of aromatic compounds. A common denominator for these chemicals, however, is hydrophobicity – many of the essential oils are lipophilic (hence their name). As such, it is reasonable to hypothesize that they would associate with the plasma membrane. Some evidence support this intuition: studies show that flavonoids, a family of compounds, are synthesized by a membrane-associated flavonoid enzyme complex. Yet, a lot remains to be discovered.

In the meantime, try chewing a few oregano leaves — I did this the other day. Its strong, almost unpleasant taste is reason enough to throw off a many organisms, large or small.


Thyme leaf oil gland. Coloured scanning electron micrograph (SEM) of part of the leaf surface of the herb thyme (Thymus vulgaris) showing an oil gland.


2 Responses to “Aromatic Compounds in Plants: Functions Beyond Adding Deliciousness”

  1. Radha December 8, 2012 at 12:04 PM #

    Njuter av din inspirerande blogg!

  2. vayumi December 9, 2012 at 7:28 AM #

    Reblogged this on FireBellies and commented:

    Aromatic Compounds in Plants: Functions Beyond Adding Deliciousness

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