Stem senses
Smell
Plants can detect or "smell" a type of odour molecules known as volatile organic compounds (VOC's) which are released by neighbouring plants . These compounds cause plants to react differently depending upon the chemical composition of the compound . These odour signals are crucial to each individuals survival and the survival of plant communities, allowing plants to react appropriately to any threats they may face.
How a plant smells
Once a plant releases a volatile organic compound it travels through the air and lands on the surface of another plant. On the surface of the plants leaves are receptors. In order to affect the plants behaviour the chemicals must move into the plants cell and build up to a high enough concentration. Once the chemical is at a high enough concentration within the plant cell, it is then able to change the plant behaviour by turning on certain genes which trigger different responses.
VOC's can take a long time to build up in the plant cell. This means that unlike in animals, a plants response to odour is much more gradual. Despite this, researchers estimate that plants can actually detect more odour molecules than animals because of the number of genes plants have.
slow signals
Key definitions
VOC's: organic chemical molecules which are emitted as a gas.
Receptors: cells which detect environmental change and respond to the change.
Gene: a section of DNA which acts as a set of instructions for certain cell functions e.g. protein synthesis.
Herbivore: an organism which feeds exclusively on plants.
Pathogen: a disease causing organism.
Pesticide: chemical compounds which target and kill species considered pests.
Herbicide: a substance used to kill unwanted vegetation.
How plants use VOC's for protection
A call for help
Some plants when injured by feeding herbivores have developed a defensive strategy which benefits both the plant and predatory insects. when a plant detects injury from feeding insects it releases VOC's. These compounds attract the natural enemies and predators of the feeding herbivores. The predatory insects will then feed upon the herbivores which sit on the plants surface. This strategy removes the threat from the plants by killing the attacking herbivores but also benefits the predators by providing them with a meal.
Virus invasion
When pathogens infect a plant, plants have been shown to release VOC's which can inhibit the growth and spreading of the pathogen through their tissues. The VOC's can also be detected by neighbouring plants. If the chemical is released in a large enough quantity the receiving plant will turn on defence-related genes. These genes will help to prime the plants defences in case the pathogen also spreads to them.
I heard it on the grape vine
Plants are able to send out VOC's as warnings to neighbouring plants about potential threats.
Neighbouring plants which receive the VOC signals prepare themselves for potential stresses. The plants will be able to determine the threat from the chemicals which make up the VOC. For example, if a plant receives a VOC signal which means 'herbivore attack', the receiving plant will prepare for the attack before it even begins.
Fact!
The odour compounds plants release are the same chemicals which give essential oils their distinctive smells.
Fact!
(Hover over me)
Practical application
The destruction of crops by pests is a common issue for farmers. Commonly farmers use pesticides which when applied to the plants surface, kill any insects feeding on the crop. Whilst effective the use of pesticides is associated with environmental pollution and food safety issues. The use of VOCs to prevent pest attacks has been suggested as a less damaging alternative to pesticides. By using certain chemicals farmers can prime their crops to defend themselves, as well as increase their tolerance to environmental factors. VOC's have also been found to inhibit the growth of competitive plants, suggesting they could also be used to tackle weeds without the use of herbicide.
Summary
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Plants use volatile organic compounds to communicate to neighbouring plants about environmental changes
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VOC's travel through the air and are detected by receptors on the surface of a plant
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A high concentration of chemical must build in plant cells before the plant's behaviour changes. Therefore, scent is considered to be one of the slowest ways plants can detect and respond to environmental change
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When plants detect certain VOC's they can prime themselves for attack, and release defensive chemicals with multiple effects
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It is thought VOC's could be used in farming as an alternative to damaging pesticides and herbicides