As Jane J. Lee writes for National Geographic:
The next time you wander amongst the produce in your local market, think about this: Those fruits and veggies are still alive. Though they may not be able to jump up and move, new research shows that some vegetables and fruits exhibit circadian rhythms, and can adjust their defensive compounds and nutrients accordingly.
Janet Braam, a plant biologist at Rice University in Houston, Texas, and a researcher in the study, told National Geographic that circadian clocks tell plants when the seasons change due to changes in the length of days. The circadian clocks also help plants stave off attacks by insects. Plants know when the insects eat, she added.
In one plant, called Arabidopsis, compounds called glucosinolates that protect them against pests are under the control of the circadian clock. As Andy Coghlan writes for New Scientist, "These have been found to inhibit some cancers in rats and mice, and there has been some suggestion that they reduce cancer risk in humans."
The researchers found that cabbages on the same day and night schedule as cabbage looper moth caterpillars were the least damaged by the insects, as compared with cabbages whose schedules were out of synch with that of the moths. (By contrast, those cabbage samples in the study that experienced "daylight" hours when the caterpillars were experiencing "nighttime" hours lost 20 times more tissue when attacked by insects.) "What's more, levels of 4MSO, a glucosinolate with enhanced anti-cancer properties, was two to three times as high in cabbages kept to their cycle as they were in vegetables whose circadian rhythm had been disrupted," New Scientist writes.
The researchers then moved on to other fruits and vegetables, and found that lettuce, spinach, zucchini, sweet potatoes, carrots, and blueberries showed the same resistance to the cabbage looper mother caterpillars as long as they were on the same 12 hour light and 12 hour dark cycles as the insects. And this was true even though the researchers did not discover what chemicals in those plants are helping them to repel predators, New Scientist writes.
Braam suggested to New Scientist that retailers could offer customers extra health benefits by keeping freshly harvested produce to its natural circadian cycle rather than transporting and shipping them in the dark. "Perhaps we should be storing our vegetables and fruits under light-dark cycles and timing when to cook them to enhance their health value," she said. In the raw foods community, since we don't cook the produce, a better question might be: Will manufacturers redesign refrigerators to ensure that the stored produce is exposed to light and dark according to circadian rhythms, instead of keeping them in the dark all the time?
Mike Covington, a plant biologist at the University of California, David, who was not involved in the study, told National Geographic: "This is an approach that you can take to increase the post-harvest health of the crops without having to spray them with pesticides or introduce genetically modified organisms."