If plants had a language, what would it sound like? For years, the concept of plant communication was fairly nonexistent, and hypotheses about trees sending each other electrical signals as they were being cut down were considered lunatic at best [1]. The botanical world has largely been viewed as a silent one, but the past few years of research have finally unveiled the buzz of constant communication between plants, all unheard by human ears.
As it turns out, plants need to ‘talk’ to each other for many of the same reasons humans have developed verbal and body language: to coexist successfully, express physiological needs, and cooperate in protecting the overall community. Only recent advancements in technology have allowed humans to gain insight into this unheard conversation – and now we can see it as well. Scientists have managed to visually prove that plants warn each other of impending dangers, negotiate with their nearest neighbors, and send messages throughout their populations when necessary.
For example, a curious phenomenon called ‘crown shyness’ refers to the learned behavior of plants, especially large trees, to redirect and divert growth when their leaves begin to brush up against the leaves of surrounding vegetation [1]. It’s almost the botanical equivalent of body language. More common, however, are chemical signals that spread throughout the body of one plant and then to those closest to it. Roots of one plant exude organic compounds into the soil that then pass into nearby plants through their roots, giving neighbors information on each other’s well-being. When tested on corn seedlings, researchers found that seedlings would direct growth away from plants whose roots were emanating chemical signals of distress in an effort to avoid the same stressors, and would also rely on these signals to reorient themselves if they sensed they were growing too close to each other [2].
The ability of plants to communicate with each other is crucial in defending against external threats like herbivory, chemical pollution, and even lumberjacks. Scientists had previously inferred that plants could warn each other of danger after one individual was attacked, but molecular technology has recently provided a remarkable visual representation of how the process actually works [3]. When a plant is attacked – say, by an herbivorous caterpillar – the site of the wound triggers a release of glutamate (a neurotransmitter that is also found in animals), which causes a change in calcium ion (Ca2+) concentration that spreads throughout the plant in minutes. The electrical signal then jumps to other surrounding plants, resulting in a chain reaction [4]. In cases such as an attack from a voracious caterpillar, this rapid alert system is useful because it allows the undamaged leaves to quickly mount a defense response, which usually involves the production of hormones that make the leaves toxic or unappetizing [3].
This entire process occurs silently and is virtually undetectable – or was, until scientists created a mutated species of Arabidopsis in which calcium concentrations could be seen under fluorescent light [4]. The final effect (seen in image) is a visually stunning reminder of the secret signals that lie beneath the surface.
References:
The Guardian. Plants ‘talk to’ each other through their roots. https://www.theguardian.com/science/2018/may/02/plants-talk-to-each-other-through-their-roots (accessed October 24, 2018).
Elhakeem, A.; Markovic, D.; Broberg, A.; Anten, N.P.R.; Ninkovic, V. Aboveground mechanical stimuli affect belowground plant-plant communication. PLoS ONE 2018, 13(5): e0195646.
Interesting Engineering. New Discoveries Made in How Plants Warn Each Other of Danger. https://interestingengineering.com/new-discoveries-made-in-how-plants-warn-each-other-of-danger (accessed October 24, 2018).
Toyota, M.; Spencer, D.; Sawai-Toyota, S.; Jiaqi, W.; Zhang, T.; Koo, A.J.; Howe, G.A.; Gilroy, S. Glutamate triggers long-distance, calcium-based plant defense signaling. Science. 2018, 361(6407), 1112-1115.