Those other senses most don't know about (via: Finer MindsSee a larger image)

As humans, we have five primary senses. These include sight, sound, smell, taste ,and touch, along with another few lesser-known ones. We use these senses to derive sensory information about our surroundings. Obviously, these senses aren't unique to humans. In fact, over the years, we've found that creatures throughout the animal kingdom use very fascinating mechanisms to derive this same information. Granted, certain senses are more profound on other species (like sight, for instance. we know that many creatures can see in infrared), and many species have senses that work differently than ours do. Plants aren't an exception to this rule.

Recently, a team of researchers published a paper suggesting that the senses of plants are far more advanced than what was previously thought. Not only that, but they have the capability to identify certain sounds - like the sounds of insects that chew leaves - and respond accordingly.

"Previous research has investigated how plants respond to acoustic energy, including music," said Heidi Appel, a research scientist from the Division of Plant Sciences in the College of Agriculture, Food and Natural Resources.

"However, our work is the first example of how plants respond to an ecologically relevant vibration. We found that "feeding vibrations" signal changes in the plant cells' metabolism, creating more defensive chemicals that can repel attacks from caterpillars."

 [Reference: University of MU]
A caterpillar feeding on an Arabidopsis plant (Credit: Roger Meissen)

In order to come to this conclusion, Appel and a collaborator from the Division of Biological Sciences at MU placed caterpillars on Arabidopsis (a genus in the Brassicaceae family, related to both cabbage and mustard) fitted with a small piece of reflective material. They then pointed a laser at the reflective material, subsequently measuring how the leaf slightly shifted in position as the caterpillar chewed.

After those measurements were recorded, they played one set of plants the recordings that were set to vibrations mimicking the feeding; they left another group of plants in complete silence.  Later on, they allowed the caterpillars to feed on both groups, learning that the plants who had heard the vibrations produced substantially MORE mustard oil (a chemical the caterpillars find repulsive).

"What is remarkable is that the plants exposed to different vibrations, including those made by a gentle wind or different insect sounds that share some acoustic features with caterpillar feeding vibrations did not increase their chemical defenses," Cocroft said.  "This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration.'"

In the future, the men will focus their attentions on determining how the plants pick up on the vibrations. They also hope to learn exactly which complex vibrational signal is the most important (along with how powerful each of them are), which, by proxy, might reveal how each of the mechanical vibrations they feel interact with other sensory information. It's especially important to learn exactly how they use this information to enact the protective responses the researchers witnessed against pests and potential threats.

"Plants have many ways to detect insect attack, but feeding vibrations are likely the fastest way for distant parts of the plant to perceive the attack and begin to increase their defenses," Cocroft said.

Prior to this study, we knew that plants react to wind, touch and even pressure, but the insight into how audio, vibrational and chemical information collaborate is brand new and might even be most important when it comes to understanding plants defense mechanisms.

"Caterpillars react to this chemical defense by crawling away, so using vibrations to enhance plant defenses could be useful to agriculture,'" Appel added.

It's an extremely cool revelation because it blasts open the floodgates for additional research into plant behavior, potentially showing that "plants have many of the same responses to outside influences that animals do, even though the responses look different."


The study, called "Plants respond to leaf vibrations caused by insect herbivore chewing,"was recently published in the peer-review journal, Oecologia.

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