Scientists have known for many years that plants respond to acoustical stimulation, such as music. While that information is helpful in understanding plant life, it hasn’t necessarily been important in the realm of the agricultural industry.
One element missing from those types of studies was information about why plants respond to sounds as they do and the significance of those responses. In their experiments, Appel and Cocroft chose to study sounds common to the natural environment of plants.
A wide range of plant-borne vibrations comes from sources such as wind and the sounds of other insects in the environment. The vibrations provide a wealth of information about insect activity on plants.
Within the insect community found on plants, ecological and social interactions such as locating mates, attracting mutualists and exploiting plant resources are communicated through plant-borne vibrations. Appel and Cocroft thought maybe the plant was using this information too.
First, they recorded vibrations of a potted plant leaf caused by caterpillar feeding. These vibrations were then played back to the leaf so it moved in the same way in the absence of a caterpillar.
Then the plants were challenged with caterpillars and the leaf chemical defenses were measured. Leaves that had received the feeding vibrations made more chemical defenses than those receiving the “silent” control.
“We found that vibrations produced by chewing herbivores are an important source of information for plants,” Appel says. “Plants can detect and use this conspicuous, reliable and rapidly transmitted source of information about herbivore feeding and transmit it to tissues far from the site of attack to respond quickly to the threat of herbivory (insect) attack.
“Everyone knows plants can see things because seedlings will grow toward light on the kitchen windowsill,” Appel says. “They detect light, odor, gravity and touch. We now know that they also sense sound vibrations. Why are we surprised? The systems they use to sense things just aren’t in specialized organs like ours.” FG
PHOTO: Research indicates plants respond to various insect signals to determine plant response. These signals include chewing vibrations, odor and touch, and may one day lead to precision sensors to determine insect invasion for spot treatment options. Photo courtesy of Roger Meissen, Bond Life Sciences Center.
