Did you think that learning from experience was something done exclusively by higher organisms like us, while every organism without a brain (or at least a network of neurons) to its name was doomed to forget everything that happened to it throughout its uncomplicated life, and retain nothing learned by generations past.
Plants can teach us a thing or two about dealing with the ups and downs of life. They may have evolved the ability to forget stressful situations, as a way of dealing with highly unpredictable environments.
Some plants have “long-term memory”. For instance, some perennial grass species seem to remember drought and are better able to defend against damage from excessive sunlight than plants that haven’t been through an earlier drought.
Such experience helps prime plants to produce the necessary proteins and chemicals at short notice should stressful conditions recur.
Plants can preserve such memories across generations. Memory is more the exception rather than rule.
Better to forget?
Generally plants are good at forgetting, while being epigenetically primed against previously experienced stress can be beneficial, it also comes with costs. You could have an organism that’s spending way too much energy transcribing genes that really aren’t necessary at a specific time,
What’s more, such memory can be bad for future generations. For example, drought-stressed Polygonum hydropiper, a knotweed, passes on its stress response to seedlings, which become smaller, with slower-growing roots – even if they are grown in a drought-free environment.
Whether a plant forms a memory depends on what happens after a stressful experience. During this “recovery phase”, the plant can either consolidate its stress response and remain genetically primed, or reset itself to its prior state.
Brains Aren’t Needed for Making Memories
That’s what we know now, the sensitive plant, Mimosa pudica closes its leaves in response to touch or sudden stress. And, through observing how M. pudica plants responded to repeatedly being exposed to a stressful situation that didn’t cause them harm, researchers discovered that these plants could learn.
The plants very quickly stopped curling their leaves (which takes precious energy) in response to being “alarmed” but not harmed, showing they had learned that, in this scenario, leaf-closing was a waste of time. What’s more, when exposed to the same “scary” situation one month later, the plants didn’t bother closing their leaves in response, demonstrating they had “remembered” that earlier lesson they’d learned.
For a new memory to be formed, a plant has to make a protein that will affect its own DNA, affecting future behaviour.
Plants also have “short-term memory”, which doesn’t depend on DNA and RNA.