Jane J. Lee writes at National Geographic:
A study published online today in the journal Current Biology found that store-bought cabbage, lettuce, spinach, zucchini, sweet potatoes, carrots, and blueberries respond to light-dark cycles up to about a week after harvest.
And when the produce was kept on the same light-dark cycle as a predator—cabbage looper moth caterpillars (Trichoplusia ni)—it was better able to resist attacks.
Circadian clocks tell plants when the seasons change due to variations in day length, saidJanet Braam, a plant biologist at Rice University in Houston, Texas. But the clock is also critical in plant defenses against insects.
“[Plants] know when the insects eat,” said Braam, who is a co-author on the recent study, “so they can prepare a defense in advance.”
Braam and colleagues knew that levels of protective compounds called glucosinolates were under the control of the circadian clock in a plant called Arabidopsis. Part of the mustard family, Arabidopsis is related to produce including cabbage, broccoli, and cauliflower.
So the researchers decided to see if they could catch similar results in food crops like cabbage.
Braam and colleagues took store-bought cabbage and cut one-inch (three-centimeter) circles from the leaves. They then “trained” their cabbage disks to a circadian rhythm by exposing the samples to 12 hours of light and 12 hours of dark for three days.
They measured levels of glucosinolate, including a compound called 4MSO that has anticancer and antimicrobial properties, at four-hour intervals. The team then exposed the disks to cabbage looper moth caterpillars that had also been trained to the 12-hour light, 12-hour dark cycle.
Cabbage disks on the same schedule as the looper moth caterpillars suffered the least amount of damage from the insect, while cabbage samples out of synch with the caterpillars’ schedule—which experienced “daylight” hours during the caterpillars’ “nighttime” hours—lost 20 times more tissue when exposed to the hungry herbivores.
Read more here.