The Psychology of Plants – Do they feel, sense and remember?

Do plants feel, sense, remember? This is one of the questions that confuse and amaze many people. Knowing the details of some of the researches that were carried out on plants would leave us surprised. We all knew from our primary education that Plants use light not only for photosynthesis but also as a signal that changes the way plant grows. So, the question is ‘How plants sense light to regulate their development?’.  It has been discovered that a unique group of genes is discovered in plants which determine if they are in the light or in the dark.

Do plants have a sense of smell? When we (Humans) smell something, we sense a volatile chemical that’s dissolved in the air and then react in some way to this smell. By the same way plants also react in their own way to smell. The clearest example in plants is what happens during fruit ripening. we may have heard that if we put a ripe and an unripe fruit together in the same bag, the unripe one will ripen faster. This happens because the ripe one releases a ripening pheromone into the air, and the green fruit smells it and then starts ripening itself. This happens not only in our kitchens but also, or even primarily, in nature. When one fruit starts to ripen, it releases this hormone which is called ethylene, which is sensed by neighboring fruits, until entire trees and groves ripen more or less in synchrony.

Another example of a plant using smell is how a parasitic plant called Dodder finds its food (Dodder is a thread like yellow or orange stem that grows rapidly entwining and covering their host plants). Dodder can’t do photosynthesis, and so has to live off of other plants. The way the plants find the host plants is by smelling. A dodder can detect minute amounts of chemicals released in the air by neighboring plants, and will actually pick the one that it finds tastiest! In one classic experiment, scientists showed that dodder prefers tomato to wheat because it prefers the smell.

Monica Gagliano, an associate professor of biology at the University of Western Australia wrote an interesting development she had come across her research. She’s got a plant that not only “remembered” what happened to it but stored that memory for almost a month. She got a bunch of Mimosa predicts, put them in pots, then loaded each one onto a special plant-dropping device using a sliding steel rail. Each potted plant was dropped roughly six inches, not once, but 60 times in a row at five-second intervals. The plants would glide into soft foam that prevented bouncing. The drop was sufficiently speedy to alarm the plant and cause its teeny leaves to fold into a defensive curl.

Six inches, however, is too short a distance to do harm, so what Gagliano wondered was: If she dropped 56 plants 60 times each, would these plants eventually realize nothing terrible was going to happen? Would any of them stop curling? To find out, she kept going with her experiment. She observed that some individuals did not lose their leaves fully when dropped. In other words, plants seemed to figure out that falling this way wasn’t going to hurt, so more and more of them stopped protecting themselves. By the end, they were completely open.

Is this evidence of remembering, or is it something else? Maybe, all we’re seeing is a bunch of exhausted plants. Curling is work. It takes energy. After 60 drops, these plants may simply be pooped out—that’s why they don’t trigger their defenses. But Gagliano, anticipating this question, took some of those “tired” plants, put them in a shaker, shook them, and instantly they curled up again. This is something new and is the best explanation for the plants change in behavior. They didn’t curl up again because “before” they’d learned there was no need. And they remembered. A week later—after the shakings—she resumed her drops, and still, the plants failed to get alarmed. Their leaves stayed open. She did it again, week after week, and after 28 days, these plants still “remembered” what they’d learned. That’s a long time to store a memory. This entire experiment suggests that plants remembered what has happened to them and acted accordingly.

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