Plant & zo
The science of plants and more
Don’t touch me
Plants are most often not recognised for their speed. Their reaction is often hardly visible with the naked eye, to see them moving you really need some patience. But as always there are some exceptions. Those that react quickly. To catch insects. Or to scare them away. They do that without a central nervous system or muscles, required for a fast reaction from animals. And they still manage it. Now Japanese researchers lift a tip of the curtain to reveal how this is possible.
One of those quick plants is the plant touch-me-not. It does not like to be touched. When you dare to touch it anyway, then it closes its leaf. When a grasshopper takes a bite for a leaf, then it closes super-fast. So quick that the leg of the insects gets caught between the blades of the leaf. All the other leaves of the plant follow, and close. Not really a relaxed place to have something to eat.
The researchers studied what happens inside the leaf after touching or wounding. They did this using a sensor to visualize the calcium concentration inside the cell. After touching, the researchers noticed a light of the sensor quickly traveling along the midvein of the leaf. From where the leaf was touched towards the stem of the plant. Whereafter the leaf closed.
Calcium signals are essential to be able to react quickly
When the researchers wounded the leaf, by cutting it with some scissors, then the sensor lights up near the wounding site, and the leaf closes here. After a short break the researchers noticed the light quickly travelling further alongside the midvein of the leaf, and the closing of the rest of the leaf. A wound is thus giving two calcium signals, while touch results in only one. Allowing the plant to decide if it needs to close all its leaves or only one.
Knowing now the kind of messenger the plant releases after touch or wounding, they decide to block these to see what would happen. Touch-me-not plants that could not transmit any signals did not close their leaves after touching of wounding. In real life, the researchers observed, this meant that the plants were visited more often by insects. There they could with all the time of the world eat from touch-me-not its leaves.
Showing that these signals are essential to be able to react quickly. But how the calcium signal causes the closing of the leaves is still unknown. That secret touch-me-not is keeping for itself for the moment.
Hagihara, T., Mano, H., Miura, T., Hasebe, M., and Toyota, M. (2022) Calcium-mediated rapid movements defend against herbivorous insects in Mimosa pudica. Nat Commun 13, 6412. https://doi.org/10.1038/s41467-022-34106-x
You can see the calcium signal traveling alongside the midriff of the leaf in videos accompanying the article. For when it is touched and for when it is wounded.