Do plants feel pain?

Plants and animals are living beings that work in very different ways: while the former transform the energy of the sun into food, the others cannot do that, but we do have the ability to move from one place to another. Our lifestyle differs so much from that of plant beings, that it is logical that we have created a dividing barrier that separates both worlds.

However, it is important to remember that when it comes to moving forward, each and every one of us is ‘born’ with a strong survival instinct. Therefore, it is fascinating to wonder if plants feel pain , since that is a sensation that sets in motion a series of reactions in the body to precisely reduce this discomfort as soon as possible.

Plants don't feel pain, but damage does

Before proceeding, it is important to know what pain is. Although we have all felt it before, pain is a signal from the nervous system that tells us that something is causing us discomfort . And of course, knowing this many will say that plants do not feel it, because they do not have a nervous system, or maybe they do?

Well, for a living being to feel pain and recognize it as such, it must have neurons that are in charge of identifying that sensation. Plants lack neurons, making it impossible for them to feel pain . Now this is a half truth, because it has been discovered that they have cells that produce and emit electrical signals, (almost) like the neurons in our brain do.

So while they don’t feel it, they do react to damage . And this is something that researchers from the United States and Japan discovered, who produced a study that was published in Science in September 2018. This study consisted of inducing damage to a leaf of a genetically modified plant that produces a protein that lights up when calcium reacts in some way (when its production increases, for example).

The results were astonishing. Apparently, when it is damaged, the amount of calcium in the cells increases considerably, and as a consequence, a fluorescent protein sensitive to this mineral lights up.

In this video, accelerated because the reaction time of a plant is slow, at a millimeter per second (ours is up to 120 meters per second), it shows how proteins light up after a leaf when bitten or cut . But scientists went further. They wanted to know why calcium increased so much , what it was that gave him, let’s say, the starting gun.

They were not very complicated. In humans that signal is given by glutamate, a neurotransmitter that is responsible for communicating some neurons with others. Well, this time, they put a few drops of glutamate on a normal plant , that is, non-transgenic.

What does this mean? Well, very simple: that glutamate is capable of imitating the damage signal of plants . But for that to be true, plants must be able to identify this neurotransmitter, and they can only do so if they produce it themselves, as this study showed they did in 2013.

But if this seems surprising to you, there is even more. When a plant is subjected to significant and / or constant damage , such as that caused by a lot of herbivorous animals that feed on its leaves day after day, it will react producing more calcium, whose signal in turn will stimulate the production of chemicals toxic to these animals.

One of the cases that caught the most attention was that of the kudúes and the South African acacia trees, and that was published in New Scientist in 1990. In the 1980s, the hunt for the kudú increased greatly, too much, to the point of that the species was seriously endangered. Therefore, a group of people decided to take them to a safe place, wired so that they could not go out, and where there were several copies of acacia that they could use as food.

The kudues died when the acacia trees were stressed

What no one expected was that the animals began to die poisoned … by acacia trees. These, to the be subjected to such stress began to produce a gas called ethylene, which caused the leaves produce tannins , substances that took the lives of thousands of kudu. This gas also served to alert the other acacia trees that had not yet suffered damage, which began to produce tannins in their leaves to protect themselves from the kudúes.

Once again, the increase in calcium production, as a consequence of glutamate, was the trigger for this increase in tannins in the leaves. Even the smell of freshly cut grass is actually a call from plants to those who can be of great help , such as parasitic wasps that lay their eggs on caterpillars that feed on grass.

So, summarizing. Plants do NOT feel pain, but when they are under great stress they react, and they can do it in really curious ways.

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