When you hear the term, “intelligence”, most of the time you think about it in an anthropogenic centred way. Yes, humans have a complex brain with interconnected neural networks. As a result, humans have many abilities such as making their own decisions, problem-solving, reasoning, learning and memorizing. Not only humans, other animals also have a different kind of neural systems. Even though some animals do not show well-developed brain organization, they have different scales of neural cells assemblies. These animals can manipulate their behaviour by responding to stimuli to overcome environmental challenges. They perceive signals, respond, learn and memorize the experiences in their lifetime. The collection of all these cognitive abilities can be considered altogether as intelligence. However, there is no universal definition for it. Do you think that intelligence only limits to humans and animals?
Figure 1
Recent studies suggest that intelligence may exist even in plants. It is a bit controversial because many of us think that intelligence connects with neural systems. In the animal aspect, it is true. Plants do not have neurone systems. They are silent, sessile organisms. However, we cannot say the silent green world is not intelligent! They perceive external signals and respond to them. This response can be considered as the behaviour of plants. Unlike the muscular movement of animals, plant behaviour is related to the changes in growth. Even though muscular movements are powerful and fast, growth responses are slow and below our visual capacity to see it without measuring. Initial cell signalling is associated with action potentials and changes in cytoplasmic Ca2+ levels like animals. The speed of the process differs between plants and animals. Intracellular communication exists in plants like animals. Plants use phytohormones such as auxins, gibberellins, cytokinin, abscisic acid, ethylene, salicylic acid and jasmonate. Hormone-based regulation also exists in animals. In plants, plasmodesmata enable movement of proteins, nucleic acids and other small molecules. They act as channels for the cell to cell communication. Physiological alterations occur in plasmodesmata after exposing to anaerobic or osmotic stress as adaptation. Similarly, the dendrites in neuronal cells alter to amplify the communication pathway during the learning process in animals. Thus, we cannot underestimate the abilities of the plants.
Dr. Monica Gagliano is a biologist who studied plant behaviours and their cognitive abilities. During the panel discussion at the World Science Festival 2019 titled “Intelligence without brains”, she explained about the experimental evidence related to the intelligent plant behaviour. She conducted several researches related to plant communication, plant memory and learning capacity. The rest of the article gives you a brief explanation about one of her studies about plant learning ability.
Figure 2 : Mimosa pudica plant
For the experiment, a sensitive plant, Mimosa pudica was selected due to its ability to show leaf-folding reflux as a response to physical disturbance. Other than that, this defensive response can easily be used for studying the behavioural phenomenon called habituation. Habituation is an adaptive process that enables organisms to extract important information from the environment while ignoring stimuli and events that are repeatedly proven to be irrelevant. It is a simple form of learning. Remembering the previous experience is crucial for the habituation process. Learning and remembering are features of intelligence. Thus, habituation represents a basic level of intelligence. To determine the degree of habituation, she designed special plant-dropping set up for training the Mimosa plants. These plants were subjected to seven consecutive trains of 60 drops with 5 or 10 seconds inter-stimulus intervals.
Figure 3: The plant-dropping set up
Here, they observed that Mimosa leaves reopened even before the first train of droppings was completed. By the end of the training, leaves completely remain opened. The leaf-folding reflux habituates rapidly. It means that Mimosa plants can show learning behaviour! Now, are there any questions coming into your mind? You can say that this phenomenon can be a result of energy depletion or fatigue. To answer this question, they placed trained plants on a shaker for giving a new stimulus. If the stopped leaf-folding reflux is caused due to fatigue, these plants would not be able to respond to new stimuli. Surprisingly, Mimosa leaves showed leaf-folding reflux again. There is no doubt that Mimosa plants can learn! Dr Monica Gagliano also showed that habituation could persist for about a month. It indicates that Mimosa plants can remember the details about stimuli by an unknown mechanism. These plants learn to ignore non-harm stimuli. This behaviour minimizes energy loss and maximizes light capturing. They change their normal behaviour based on the novel condition for optimum survival.
What do you think about plants now? Are these plants intelligent or not? Green life has a kind of intelligence, which needs to be studied more in the future. Let’s think differently about the silent green world. Then you will realize the secrets that exist within plants!
References
https://link.springer.com/article/10.1007/s00442-013-2873-7
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4845027/
https://academic.oup.com/aob/article/92/1/1/177536
https://www.bluesci.co.uk/posts/a-case-for-plant-intelligence
Image courtesy:
Featured Image: https://cdn.the-scientist.com/assets/articleNo/66101/aImg/32588/plant- consciousness-thumb-l.png
Image 01: https://media.wnyc.org/i/1860/863/c/80/1/3_brain-vs-plant.jpg
Image 02: https://lh3.googleusercontent.com/proxy/2dzAOZfl4OsDsXUorB5gXwvQHgXK1tS3wHToWkbarN9UKwpi15fn_7oVNPYCtCH-U85si6ipJ3EnaKamvce_CVbbCA90Mx3dO0xD6dyaKm6k0kE2TvUskv5TYbM
Image 03: https://www.nationalgeographic.com/content/dam/science/phenomena/curiously-krulwich/rights-exempt/files/2015/12/2GIF_Plant-Drop.gif
