Vegetables Rely on Internal Clocks for Defense

June 25, 2013 -- That cabbage in the produce aisle? It's smarter and more alive than you think.

A new paper published in the most recent issue of Current Biology says that not only can cabbages tell time, but the clock also plays a key role in their defense mechanism against pests. Not only does it protect them from unwanted critters, but it also could make it healthier when they arrive on the dinner plate.

Janet Braam, a professor of cell biology at Rice University in Texas that conducted the study, says that the secret lies in how the cabbage's defense syncs up with its circadian rhythm. The rhythm itself is a type of biological clock that refreshes every 24 hours.

She explains that the defense comes in the form of glucosinolates. "They're a group of chemical compounds that discourage insects from eating the plant," she told ABC News. "The level of glucosinolates varies depending on the time of day, and it appears that they are highest at the time of day when insects are most likely to eat them."

The glucosinolates themselves don't just benefit plants. "There's many studies that show that glucosinolates have potent anticancer effects," Braam said. If the lights of a refrigerator were programmed to sync up with the hours of the day, it might make veggies healthier for us in the long run.

To test whether the cabbage's defense is tied to the clock, Braam and her colleagues either bathed cabbages in constant light or raised them in constant darkness. After unleashing cabbage looper caterpillars onto the different groups of cabbages, they observed the insects eating twice as much of the leaves reared in constant light and darkness compared to the one raised in normal light conditions.

RELATED: Gin and Tonics at Risk From Foreign Invader

Another group of cabbages were raised in a completely desynchronized light environment from the caterpillars. When the lights were shut off for the critters, they were turned on for the plants, and vice versa. As seen in a time lapse video recorded by Braam, the caterpillars ate nearly 20 times more of this cabbage compared to the normally raised one.

In addition to cabbages, Braam also observed these effects in several other vegetables that do not have glucosinolates, including spinach, sweet potatoes, and carrots.

"We don't know what chemicals are going up and down, but they showed enhanced defense with a normal light/dark cycle," Braam said.

If glucosinolates and other molecules are crucial to the cabbage's health, why link it to the clock instead of just always keeping it on reserve?

Daniel Kliebenstein, a co-author on the paper and a plant biologist at University of California-Davis, suggests it has to do with conserving energy.

"Insects, just like people, eat at different times of the day," he said. Rather than constantly have glucosinolates at the ready, the plants have learned to optimize their production so that it better allocate its energy to other activities.