Cabbage circadian clocks
tick even after picking
Daily cycles help
vegetables fight off hungry caterpillars
By Cristy Gelling in Science News
Cabbages with jet lag
are less nutritious and more vulnerable to insect pests.
Fruits and vegetables
have an internal clock that can be reset by a daily cycle of light and dark,
but storing produce in darkened refrigerators could disrupt this natural
rhythm, researchers report June 20 in Current Biology.
Plants, even after being
cropped from the stalk, are much more responsive to their external environment
than we give them credit for, says Janet Braam, a plant biologist at Rice
University. “When we harvest them they’re still metabolizing,” she says. “They’re
still alive.”
She and her colleagues
had previously found that the plant Arabidopsis thaliana schedules
production of insect-repelling chemical defenses to match caterpillar feeding
peaks. These defenses include compounds called glucosinolates, which are
thought to have anticancer and antimicrobial properties in addition to their
caterpillar-discouraging ones.
When Braam told her son
about these experiments, he joked that now he knew the best time to eat his
vegetables. She realized that cabbages — which also produce
glucosinolates — might have similar daily cycles even after being picked,
packed and shipped.
“So we went to the
grocery store, bought some cabbage and put them under dark/light cycles that
were either in phase or out of phase with our insects, and then asked whether
the insects could tell the difference,” says Braam.
Like Arabidopsis,
the cabbage leaves had daily glucosinolate cycles if the vegetables were
exposed to alternating 12-hour periods of light and dark. Caterpillars on a
cycle offset by 12 hours to the cabbages’ (so the cabbages’ dawn was the
caterpillars’ dusk) ate about 20 times more than did caterpillars on a schedule
synchronized to their food. Caterpillars also ate twice as much cabbage if the
vegetable had been kept either in constant light or constant darkness.
It’s not just cabbages
that adjust daily rhythm to better fend off caterpillars; the team found
similar results for spinach, zucchini, sweet potatoes, carrots and blueberries.
These fruits and vegetables don’t produce glucosinolates, so they must make
some other kind of defenses on a daily cycle, says Braam.
The researchers suggest
that we might improve the health benefits and pest resistance of fruits and
vegetables by storing them under lighting conditions that mimic day and night.
But Cathie Martin, a plant biologist at the John Innes Centre in England, is
skeptical.
She says most postharvest vegetable losses are from fungal
infections, not the insects that eat vegetables in the field. And cabbages are
sometimes cold-stored for months in the dark before being sold. Cabbages lose
the clock-regulated pest resistance about a week after harvesting, the new
study shows.
“But maybe I’ll be
proven completely wrong,” says Martin. “Maybe one day we’ll all have little
LEDs in the fridge.”
CITATIONS
D. Goodspeed et al.
Postharvest circadian entrainment enhances crop pest resistance and
phytochemical cycling. Current Biology. Published online June 20, 2013.
doi:10.1016/j.cub.2013.05.034 [Go to]
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