The Sense Of Smell Of Plants

Viti Vinci 03/12/2022

The olfactory ability of plants is in their genes, and information from odour molecules changes gene expression in them, “turning on” or “turning off” genes. The type of odour molecules they detect are called volatile organic compounds, essential for their survival and the reason for their fragrance.

Unlike in animals, which recognize odour molecules through receptors located outside the cells, which immediately triggers a change in their behaviour, in plants these molecules have to enter the cell and accumulate before they affect the plant’s behaviour. And since plants can’t move, their reactions are much slower. So, speed is not their strong suit, but they are able to recognize a much greater variety of odours.

You might say, how can they smell if they don’t have olfactory nerves? Well, no, they don’t, but plants respond to pheromones and detect volatile chemicals in the air, converting this signal into a physiological response. It is not the same system, but it is considered olfaction.

And, as we already know, these behavioural changes are part of their communication system with each other, but also between different species, for example, plant-animals or plant-insects.

An example of these changes is the way they ripen in response to the smell of certain chemicals; all ripening fruits emit ethylene and so, when they smell it, other plants respond by ripening. Thus, all fruits ripen at the same rate. And these changes are not only with respect to their ripening, but their sense of smell allows them to attract more animals to eat their fruits and disperse their seeds, and to coordinate the change of colour of the leaves in autumn.

Another example is that plants can change their smell to protect themselves from insects; if they smell a neighbouring plant that has been eaten or attacked by a bug, they set off their anti-predator defense mechanisms to make themselves less palatable to that insect and even signal SOS to other plants, letting them know that danger is imminent.

As we have said, they know when other neighbouring plants have been cut or eaten by a bug thanks to their sense of smell, even though they cannot see or touch the other plants. This means that they can detect odours with very subtle distinctions between them. So, even without a brain or a nose, plants are able to perceive, identify and react to odours.

An interesting fact about this sense of smell is how Cuscuta pentagona, commonly known as the dodder, a plant without chlorophyll, chooses a specific neighbour to obtain its nutrients for survival. This neighbour is the tomato plant; therefore, it can smell the plants next to it and choose its favourite. Once it smells the tomato plant, the dodder bends, grows and turns in its direction.

So, the next time you stop to smell the flowers, think that they might be smelling you back. Also, if you fail to keep a plant alive, don’t be too hard on yourself, your plant may simply not like the way you smell!

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