Have you ever wondered if plants feel ? Surely yes, whether due to moral or ethical convictions or simply out of curiosity, this question must have crossed your mind.
If a tree falls and no one is there to hear it, do you feel pain, do you feel lonely? If a plant is attacked, or we cut off a flower or a branch, does the plant feel pain because a part of it has been torn off?
A group of experts in plant physiology have published an opinion article on the matter, on July 3 in the journal Trends in Plant Science . His conclusion is that no, plants do not feel pain, nor do they feel in general.
Studying whether plants feel, a matter of debate
The conclusion to this conclusion is based on the results of research by Todd Feinberg and Jon Mallatt exploring the evolution of consciousness through comparative studies of simple and complex animal brains.
According to their study, only vertebrates, arthropods, and cephalopods have enough brain structure to be conscious. There are a large number of animals that do not have consciousness such as cockles, sponges , jellyfish …
The fact that plants feel implies that they have a brain or nervous structure developed so that they think, learn and choose their actions intentionally. However, plants do not have neurons so they do not have a brain either.
This contradicts and highlights the debate that has existed since plant neurobiology was established in 2006 as a new branch of biology and botany. Voices were raised against this new line of study since they argued that plants do not have any neurobiology to study.
According to Lincoln Taiz, emeritus professor of molecular, cellular and development biology at the University of Santa Cruz, there is a danger of anthropomorphizing plants, which can undermine the objectivity of the researcher. Plants and animals evolved with very different strategies. The brain is an energetically very expensive organ and plants do not benefit from developing a nervous system.
Proponents of plant neurobiology draw parallels between the electrical signaling that occurs in plants and the nervous system of animals. These parallels imply that the brain is not anything more complex than a sponge whereas the Feinberg-Mallat model of consciousness describes that a specific level of complex organization is required that is required for the subjective experience of pain.
Plant responses to pain or seizures
Electrical signaling in plants can be done in two different ways:
a) to regulate the distribution of charged molecules across membranes: for example, this pathway is what makes plants curl their leaves because the movement of ions results in the movement of water through cells and therefore both the leaves are curved. This changes its shape.
b) send long-distance messages through the organism: in this way, for example, if an insect bites a leaf, it can initiate the response strategies of more distant leaves in the plant. Apparently, this pathway is activated by the glutamate molecule, as it happens in animals, although the speed of its expansion is 2 millimeters per second, while in animals it is 120 meters per second. Although they cannot remove the insect or caterpillar from above, the plant is capable of secreting toxic substances that serve as a defense against insects.
In both cases, it seems that the plant can choose how to react to a stimulus , but the detractors of plant neurobiology emphasize that they are responses that are genetically encoded and that have been refined by natural selection. In addition, since there is no nervous structure, the subjective experience of pain does not occur.
The advocates feel that plants exemplified the apparent habituation of Mimosa pudica . In his experiment, a plant falls and its leaves roll up in defense. After the plant falls several times, without serious damage, the leaves stop curling. When the plant is shaken, the leaves curl up, apparently eliminating motor fatigue as the cause of the lack of response when dropped.
Among the hypotheses that answer this question, it is evident that the upheaval was quite violent. Given that the shaking stimulus was stronger than the falling stimulus, it does not rule out that there is sensory adaptation but it does not imply that there is learning.
In the case of another quite interesting study, the one carried out with Pisum sativum , peas, it is criticized that the controls were not well planned. In this study , we sought to relate the presence of light with a neutral stimulus (air from a fan) to the purest Pavlov conditioning . The researchers got the plants to respond to a neutral stimulus (the fan) as an anticipator of the presence of light.
Perhaps the term plant neurobiology is very ambitious given that plants do not have neurons, but rather a network of mechanisms that allow them to respond and adapt to the environment in very different ways, similar to animals but not the same.