Makahiya plants have memories and can learn, biologists find

A common sight in Philippine grasslands, the makahiya plant (Mimosa pudica) is famous for its tendency to curl up its leaves at the slightest touch, as if it were extremely embarrassed about physical contact, hence its name: "makahiya" is derived from the Filipino word for "shame" or "shyness" ("hiya"). 

 

Lightly touching the leaves causes the plant to withdraw them almost instantly, and the phenomenon is admittedly both remarkable and amusing to anyone who's tried it:

 

 

However, it seems as if the makahiya (also known as the “sensitive plant” or the “touch-me-not” in other parts of the world) doesn't just discourage touching , it probably also remembers all the times humans and animals poked and prodded at it.

 

A 'touchy' subject

 

A team of biologists from Australia and Italy decided to closely examine the makahiya in order to determine what it perceives as a “harmful” touch. The team’s findings were published in the January 2014 issue of the journal Oecologia.

 

Led by Dr Monica Gagliano from the University of Western Australia, the researchers ran an experiment, testing for short-term or long-term memory in the tiny plant by treating it like an animal.

 

“The nervous system of animals serves the acquisition, memorization and recollection of information,” wrote the scientists. “Like animals, plants also acquire a huge amount of information from their environment, yet their capacity to memorize and organize learned behavioral responses has not been demonstrated.”

 

Experience, the best teacher

 

According to the biologists, the makahiya’s well-documented leaf-folding behavior – a defensive response to physical stimuli – demonstrates “clear habituation,” and suggests that the plant may have the capacity to learn.

 

Using a special device designed to drop water on the makahiya, the researchers trained the plant’s short-term and long-term memories while switching between high-light and low-light environments.

 

Dr Gagliano and her colleagues found that the plants they tested actually stopped closing their leaves after repeated water-dropping, indicating that the makahiya plants realized that the droplets presented no real danger to them.

 

Furthermore, the plants were able to learn rather quickly; according to the biologists, it only took them seconds to adopt this behavior.

 

An excellent pupil

 

Much like how animals learn faster in a harsher environment, the makahiya also exhibited a better memory under less favorable conditions.  

 

Surprisingly, the makahiya plants actually remembered that the water droplets presented no threat to them. They demonstrated the same passive behavior even after weeks had passed, despite having been moved to a different environment.

 

“Astonishingly, Mimosa can display the learned response even when left undisturbed in a more favorable environment for a month,” the biologists observed. “This relatively long-lasting learned behavioral change as a result of previous experience matches the persistence of habituation effects observed in many animals.”

 

The researchers have an explanation for this, though. “Plants may lack brains and neural tissues but they do possess a sophisticated calcium-based signally network in their cells similar to animals’ memory processes.”

More respect for plants

 

However, the biologists also admitted that they have yet to determine the specific biological basis of the plants’ learning capabilities. On the bright side, their findings shed new light on the way we understand the similarities and differences between plants and animals. If anything, this should also serve as an effective reminder to stop disturbing plants, as the ability to learn appears to be a trait that isn't exclusive to animals alone.

 

The makahiya plants are perhaps best left to their own devices, lest they stage an uprising (or perhaps an “uprooting”) and decide to go for their “bullies” first. After all, we've already seen what innocent-looking plants can do to a horde of zombies. — TJD, GMA News