Vegetables and fruits, including the broccoli and blueberries in your refrigerator, have circadian rhythms just like humans. In humans, an internal circadian clock that corresponds to the 24-hour-cycle of light and darkness controls our sleeping and waking; it may also influence our metabolism, temperature regulation and even aging. Vegetables and fruits are just as attuned to light and dark. Even after they’ve been harvested, they continue to metabolize. How much light and dark they receive could even affect how nutritious they are.
From studying Arabidopsis, a plant related to cruciferous vegetables (cabbage, broccoli, cauliflower) that is often used in scientific studies, bioiochemists at Rice University discovered that some plants can change their production of certain chemicals. As biochemistry professor Janet Braam and other scientists report in a recent study, Arabidopsis responds to light cycles by adjusting its “defense hormones” — glucosinolates, a chemical that insects do not care for — at the very time of the day that insects come to feed on the plant (in the late afternoon, in the case of caterpillars).
Wanting to see if other plants had the same response to light, the scientists procured some cabbages from a supermarket. They exposed half to a normal cycle of 12 hours of light and 12 hours of dark and the other half to cycle that was opposite. As they had found from studying Arabidopsis, the light signaled the cabbages (even though they had been picked some time before) to produce more glucosinolates. When offered to some caterpillars, the cabbages who’d been exposed to a normal light and dark cycle had less damage.
Only cruciferous vegetables have glucosinolates. Wanting to see if other vegetables and fruits might have a similar response to light and dark, Braam and the other researchers tested spinach, lettuce, zucchini, blueberries, carrots and sweet potatoes by exposing them to different cycles of light and dark. They then offered them to caterpillars. Sure enough, the insects consumed fewer of the plants that had been exposed to the regular light and dark cycle.
Circadian rhythms also influence vitamins and antioxidants in plants so the cycles of light and dark that produce is exposed to could influence its nutritional content as well. Ars Technica points out, that these findings could influence future refrigerator design. What if future appliances could alter how much light and dark your broccoli was receives prior to your consuming it?
The Rice University researchers’ study makes (yet another) case for seeking out locally grown produce that hasn’t been in crates for who knows how long and under the fluorescent lights of a mega-sized grocery store before reaching your refrigerator. If vegetables and fruits are at their most nutritious according to natural cycles of light and dark, hothouse tomatoes may not only be lacking in taste, but less healthy. Since the beneficial substances in fresh produce are at their peak when it’s light and bright, the study makes the case for having what NPR calls a vegetable happy hour — and for making sure to include some fresh produce at breakfast and lunch.
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