The sensitive plant Mimosa pudica is famous for closing its leaves when detecting danger. This plant is perfect for the study of memory because it gives a physical sign to external influences. Indian botanist Bose thought that animals and plants shared analogous organs. These organs may look and behave differently between plants and animals but they serve the same purposes. It turns out a hundred years after he proposed this, it has been shown that plants store memories in a similar way to animals.
Calcium is crucial creating memories. Calmodulin, a calcium-modulated protein, is used to carry messengers within cells and can be found in plants and animals. Plants don’t have brains but they do have calcium based networks that seem to act in the same way.
Sensitive plants can learn to ignore an external influence if it causes the plant no harm. If you take a potted sensitive plant and drop it, it will close all its leaves. After a short time they will open again. Drop the plant over and over and soon it will stop closing its leaves. The plant has concluded that being dropped is harmless, so stops closing its leaves to conserve energy.
If a plant has been dropped and not closed its leaves, a simple brush of a leaf with a finger will still make the leaf close. The plant can detect the difference between being dropped and touched and will react differently. The memory of being dropped is retained for at least a month and probably a lot longer, maybe only being forgotten when the plant thinks it is no longer an issue.
Article: “How neurons remember”