Researchers have found they can boost levels of nutritious, cancer-fighting compounds in vegetables such as cabbage by fooling the vegetables into thinking it's a certain time of day.

Janet Braam, a biologist at Rice University in Houston, Texas, and her colleagues discovered in 2012 that Arabidopsis thaliana, a plant related to cabbages and broccoli, uses its internal biological clock or "circadian rhythm" to ramp up production of insect-fighting chemicals at the times of day when the insects are most likely to attack and feed on them.

'We understood that crops don't die as soon as you take them away from their roots ... But they're much more responsive and active than I think we were aware.'—Janet Braam, biologist

"That way, the plant prepares for the attack before it actually happens," Braam told Bob McDonald, host of CBC Radio's Quirks & Quarks, in an interview that airs Saturday.

Plants keep their internal clocks synchronized to the environment by detecting the light and temperature conditions around them.

Braam was interested to find out if plants can maintain those rhythms, after they're harvested and waiting to be purchased and eaten, since some of the insect-fighting chemicals also have anti-cancer properties.

They discovered that cabbages, spinach, lettuce, zucchini, blueberries and even root vegetables such as carrots and sweet potatoes all maintained their internal clocks after being harvested if exposed to controlled lighting in a sealed chamber. The results came as a bit of a surprise, Braam said.

"We understood that crops don't die as soon as you take them away from their roots or dig them up from the soil," she said. "But they're much more responsive and active than I think we were aware."

The researchers also found they could make cabbage leaves increase their production of an anti-insect, anti-cancer compound called gluoraphanin at certain times of the day by manipulating the light conditions to trick the cabbage's internal clock.

Typically, Braam said, cabbages produce more of the compound during the day than at night, and more of it later in the day than in the morning.

The researchers also found that if cabbage was exposed to regular light and day cycles after harvest, it remained more resistant to insect attacks during storage.

"It's beneficial to keep the clock running even after harvest," Bram said.

The findings were published Thursday in the journal Current Biology.

Son's comments sparked idea

Braam said the study was inspired by a conversation with her teenage son, after she told him about her earlier discovery of the link between the time of day and a plant's production of anti-insect chemicals. He commented that he now knew what time of day to eat his vegetables.

Knowing about the plants' rhythms may indeed make it possible to eat or preserve fruits and veggies at the time of day when the accumulation of healthy compounds peaks, Braam said.

On the other hand, storing vegetables in dark trucks, boxes and refrigerators may interfere with their ability to maintain their daily biological rhythms. However, Braam said plants are very sensitive to stimuli such as light and temperature, so it may not take very much to keep their clocks ticking.