Professor Science: the secret mumblings of plants

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Plants have feelings just like us and boy do they like to talk about them!

At first glance plants seem to be relatively simple creatures – just there to feed the rest of the world! Surely life as a plant is pretty easy as long as you have all the sunshine and water you need?

But it is not all as it seems, plants have feelings and they even talk!

Just like some people use social media to keep the world updated on every minute of their lives, plants continuously produce volatile organic chemicals (VOCs). VOC blends are constantly released into the air and reflect the current physiological state of a plant. This information is used by pollinators, such as bees, which are attracted by floral VOC blends, but also by herbivores and pathogens to identify the next victim.

Plants warn each other when they are attacked, so their neighbours can prime defence responses. The damaged plant can distinguish between mechanical damage and a herbivore attack. Chemical signals in the saliva, or spit, of the attacking herbivore, such as my diplodocus-self, trigger a stress response in the victim and it sends out a VOC distress signal. This signal is picked up by surrounding plants that can practically ‘smell’ the scent of danger and readies its defence mechanism for a fast response to the eminent attack. This signal can even be transmitted and received between many species, such as corn, tobacco and sagebrush.

Plants also talk about sex. When it comes to reproduction, animals have developed complex behaviours, such as elaborate displays or fighting to win over the female. Surely plants have dodged the bullet of intricate mating communications. Just think of flirting and dating: so many pitfalls. Surprisingly, this is far from the truth. Of course, plants do not actually flirt with words. They use pheromones to communicate. These are small molecules that transmit a chemical signal to the other plants in an area. Japanese climbing ferns tell each other which sex they are. Most flowering plants are both male and female. Japanese climbing ferns, however, can be either male or female. To ensure efficient reproduction, there needs to be a balanced ratio between male and female ferns. Releasing the growth hormone gibberellin, female ferns tell the surrounding young ferns to grow up as males.

Besides using airborne chemicals, plants also communicate underground. For the longest time the plant root has been regarded as a structure for nutrient acquisition and an anchor, nothing more. However, the notion of a ‘plant root brain’ is starting to take shape. As the roots grow and expand they encounter other roots. They are able to distinguish whether these roots are from a friend or foe. Responses to such an encounter may be friendly and result in spatial avoidance, or when an enemy has been detected, in the release of toxins.

Plants, as humans and other animals, also talk to their microbes, their microbiome. Soil is the preferred habitat for fungi and bacteria. Plant roots release sugars and chemical attraction signals, which actively recruit bacteria to the plant’s root system. The bacterial recruits help the plant by assisting with the uptake of rare nutrients, such as iron. They protect the plant from pathogens by releasing antibiotic molecules. Most importantly, they are a look-out. In response to stress signals, the bacteria release signals to the plant telling it to prepare for heat, drought, flooding, and pathogen attack.

Generally being stationary organisms, often thought of as simple and leading boring lives, plants have an underestimated need for information exchange and have developed complex ways of communicating with their environment.

So next time you’re out on a date and stuck on what to say, just say it with flowers. They clearly know how to talk the talk.

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