They’re Alive!: Circadian Rhythms in Harvested Fruits and Veggies

fresh vegetables

Research shows that fruits and vegetables are still alive after they are harvested. (Photo credit: MelindaChan/Flickr Open/Getty Images)

Have you ever considered whether the fruits and vegetables you see on the shelves in grocery stores are still alive? Do you think they die once they’re picked from the fields or off a tree? Research indicates that some life processes still function in vegetables such as cabbage even after they’ve been harvested.

Research by Dr. Janet Braam, chair and professor of biochemistry and cell biology at Rice University in Houston, Texas and her colleagues showed that circadian rhythms still occur in cabbages after they reach a grocery store’s shelves.

Circadian rhythms help plants to respond to or prepare for seasonal changes and they are also an important part of a plant’s defenses against insect predators. Throughout the day, a plant such as a cabbage produces a protective compound called glucosinolate. In addition to protecting plants against insects, these compounds are also known to contain anti-cancer and antimicrobial properties and can activate antioxidant processes in human cells, making them an important component in the human diet.

In their experiment, Braam and her colleagues purchased heads of cabbage at a grocery store. They cut out 3-cm (1-in.) samples from the cabbages’ leaves. They placed the leaves in two groups. Both groups received 12 hours of light and 12 hours of darkness. However, one group received the 12 hours of light and darkness as it would have experienced it in the field; the other group received light and darkness in opposite intervals. (That is, they received 12 hours of darkness when they would have normally received light, and vice versa.)

The researchers measured the amount of glucosinolate produced in four-hour intervals. They found that the cabbage leaves accumulated the most glucosinolate during the day, with a peak around mid-day. As light decreased and darkness increased, the production of glusosinolate also diminished. In fact, the plants had twice the amount of glucosinolate during daylight hours than they had at night.

The scientists found that the production of glucosinolate was directly related to the plant’s ability to defend against insect predators. When caterpillars were introduced into the experimental groups, the plants that received the normal light cycle were better able to fend off attack. Cabbages which received the opposite schedule of light and dark were 20 times more vulnerable to caterpillar attack.

The researchers repeated the experiment with other fruits and vegetables and were able to find similar results using sweet potatoes, lettuce, spinach, carrots, zucchini, and blueberries.

Braam plans to continue researching circadian rhythms in plants. Future study plans include gaining an understanding of the small molecules that control the circadian clocks in harvested plants and determining how the knowledge that post-harvest circadian rhythms exist could be used in a practical manner; that is, how maintaining a plant’s circadian rhythms could be used to increase the nutritional content of a fruit or vegetable after harvest.

More to Explore

Fruits and Veggies Are Alive, Can Defend Against Herbivores
Does Your Salad Know What Time It Is?
How Circadian Rhythms Give Vegetables a Healthy Boost
Vegetables Respond to a Daily Clock, Even After Harvest


  1. Jacob Nugent says

    So they defend even after they’re picked, nice.

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