Plant Communication: Volatile Organic Compounds
- Sylvia Rose
- 9 hours ago
- 4 min read
Plants form complex communication networks. One way they interact is by releasing volatile organic compounds (VOCs). These carry information among plants and to organisms such as microbes and insects.
About VOCs
Volatile Organic Compounds are organic chemicals. They easily evaporate into the air at room temperature. Plants produce the compounds through biochemical pathways for purposes like defense, signaling and attraction.
When a plant is attacked by herbivores, it can produce different VOCs carrying a message of alarm. The signals alert nearby plants, giving them time to prepare for potential threats.
Some toughen their leaves or embitter their seeds. A trick of violets is to numb smell receptors when the perceived threat takes a sniff. The potential attacker can't smell any more violets, and ideally wanders away.
Insects
Plants also communicate with insects and other animals. VOCs emitted can attract helpful insects, such as pollinators and predators of pests. Cabbage plants, if attacked by caterpillars, can release VOCs to "call" parasitic wasps. The wasps paralyze and lay their eggs in the caterpillars.
Types of VOCs
Fatty Acid Derivatives
These VOCs come from the breakdown of fatty acids and are often used as defense mechanisms. Fatty acid derivatives are released when a plant is attacked by pests. When a tomato plant is bitten by an insect, it emits fatty acids to alert nearby tomato plants to the encroaching threat.
Tomatoes have an impressive arsenal. Their defenses include physical barriers like trichomes (hairs) and chemical defenses such as the VOC methyl jasmonate. Like cabbage they can put out a call for predators.
Phenylpropanoids/Benzenoids
This group of VOCs creates sweet plant scents. The fragrance of flowers is a rich blend of phenylpropanoids and benzenoids designed to entice bees, butterflies, and other pollinators.
The corpse flower, in contrast, uses these chemicals to smell like death. Its goal is to attract flies and carrion beetles to pollinate its gigantic blossom. The stench is carried far and wide on the winds.
Amino Acid Derivatives
These VOCs, originating from amino acids, are often associated with plant growth and development. They're important for signaling between different parts of the plant.
Amino acid derivatives coordinate physiological processes and responses to environmental stimuli. They may also contribute to plant-to-plant communication related to stress responses.
Triggered by stressors, these VOCs are cues for nearby plants. When a corn plant is under attack, it releases an amino acid derivative that signals neighboring plants to ramp up their defense mechanisms.
Corn's physical defenses include the carbohydrate callose to block sap-sucking insects. Chemically, corn produces DIMBOA, which triggers callose formation, and MBOA to repel caterpillars. Some corn is genetically modified to release insecticidal Bt toxins.
Terpenoids
This is the most diverse group of VOCs. Terpenoids can attract beneficial insects, repel herbivores and unwanted microbes, and provide a defense mechanism against extreme heat.
The characteristic scent of pine trees is due to the presence of terpenoids. Mint plants emit terpenoids to repel pests and also attract predator insects.
Other Plant Communication Methods
Electrical Signaling
Similar to animals with a nervous system, plants can transmit electrical signals throughout their tissues. Signals can be triggered by environmental factors like touch, light or damage.
They facilitate fast responses, enabling plants to rapidly arm themselves and coordinate defenses. Electrical signals travel through plants at a rate of up to 16 cm/s.
Common Mycorrhizal Networks (CMNs)
Plants connect below ground through a vast network of fungal hyphae, forming a Common Mycorrhizal Network. The network empowers plants to share resources, such as nutrients and water, and to exchange information.
A plant under attack by insects can send a warning signal through the CMN to neighboring plants, preparing them for potential threats. If a willow tree is under threat, it signals neighboring willows to prepare for potential herbivore attacks through mycorrhizal connections.
Willow trees have superior defenses against herbivores and pathogens. They use salicylic acid to deter predators, and have physical defenses like flexible branches and thick bark.
Willow trees in the Sierra Nevada produce salicin, a chemical to repel browsing deer, opossums and many insects. Willows also talk to each other, sending signals to nearby plants through methyl salicylate (C8H8O3).
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