Today I invite you to take a trip with me and dive for at least a brief moment into the mind of a plant. Now I am sure you are sitting in your chair (or lying, or standing or something... you're somewhere I just know it!) thinking to your self, 
Today we will briefly discuss a recent (and fascinating!) publication in Nature: Scientific Reports titled "Learning by Association in Plants."
Orienting Your Mind To The Fact That Plants Can Have A Memory And Can Learn From It
The image above is of the plant Mimosa pudica otherwise known as the sensitive plant. This particular plant is not the focus of the study but it is what I will use to get your mind in the right state. If you are not familiar with this plant it is responsive to touch:
As you can see, when the plant is touched it constricts its leaves. It also does this despite the lack of both a brain and a nervous system! How does it work? Calcium channels. These are basically protein pores in the plants cell walls that shuttle calcium ions in or out of the cell, if you recall from chemistry calcium (Ca2+) ions have a positive charge, when you change the concentration of calcium inside the cell you can create/vary the strength of the electrical imbalance between the internal charge and external charge. This electrical imbalance creates what is known as a membrane potential (a voltage) across the cells membrane.
It is the induction of these membrane potentials that signal to the motor cells of the plant to cause the leaves to constrict like you see in the gif above (Source). Pretty neat! I explain this because it shows you a way that plants have to detect a stimulus, and if you can detect a stimulus then you can also prepare your self (chemically speaking) for the stimulus if it regularly happens.
In the case of the Mimosa pudica experiments were performed where water was dropped repeatedly on the plant causing the leaves to curl. You would think, well it's just a dumb plant, it's going to keep curling forever.... BUT eventually the plants stopped closing their leaves due to the water droplets. The plants figured out that nothing bad was happening to them, so they were just wasting energy constricting those leaves. (Source) The only way this can happen is for plants to have some sort of memory (maybe not like your or my memory, but it's a memory nonetheless).
So What About The New Publication?
In this article the authors were studying the garden pea, Pisum sativum.
The article discusses the importance of light to plants, as light is essential for both growth and survival of the plant. The plant's ability to detect queues from changing light hours are important for maximizing the amount of energy the plant is able to absorb (though ramping up photosynthetic processes when light is available).
The authors discuss how recent publications indicated that plants have been observed to acquire new behaviors through habituation (the example above of how the Mimosa pudica stopped curling its leaves, that is an example of habituation, the plant "learned" to stop curling its leaves when that stimulus was observed to be doing no harm). In this study the researchers wanted to see if plants could learn through forming associations.
To test the authors classically conditioned the plant to be used to an 8 hours light, 16 hours dark cycle. This conditioning occurred in a maze with two chambers, and the light also coincided with a fan being active. In one test group the fan and the light were in the same chamber, in the other they were in separate chambers, and finally there was a control group with no fan just light.
The plants were "trained" for three days then tested for one day. The authors then tested the plants for one day where the plants were only exposed to the fan (no light). They wanted to see whether the plants associated the potential for a light source to come from the side that they were trained to associate it based on the fan blowing on them (aka would they grow towards the wind if they were in the light + fan trial, or against the wind if they were in the light on one side and wind on the other trial).
They found that the control group grew to the side of the chamber where the light was, which was expected. However for the groups being exposed to the fan they found that for the group where the light was on the same side as the fan 62% of the plants grew towards the fan, while for the group where the light was on the opposite side as the fan, 69% grew toward the side of the chamber away from the fan. Regardless of orientation of the plants in the chamber. The plants were able to associate the light, relative to the source of wind. They were able to Learn from the experience with the wind and grow where light would be expected based upon that information.
Now mind you 62% and 69% aren't amazingly high numbers but a repeatable phenomenon is a repeatable phenomenon and would indicate there is more to a plants "mind" then meets the eye.
Additional Sources
- http://www.nature.com/articles/srep38427
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634336/
- http://www.sci-news.com/biology/science-mimosa-plants-memory-01695.html
- https://theconversation.com/pavlovs-plants-new-study-shows-plants-can-learn-from-experience-69794
- https://en.wikipedia.org/wiki/Mimosa_pudica
- https://en.wikipedia.org/wiki/Pea
All non Cited Images Are Available Under Creative Commons Licenses, The Primary Article From Nature: Scientific Reports is also Open Access and Available for Use Under Creative Commons Lisences
All Gifs Are From Giphy.com and Are Also Available for Use Under Creative Commons Licences
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