Sunflowers track sun due to internal clock, not sunlight, says new research

NEW DELHI (TIP): Everybody knows that sunflowers track the sun as it rises in the east every morning and sets in the West every evening. It has been assumed that light rays from the sun must be triggering off some mechanism in the sunflower plant causing this fascinating movement.

But scientists Hagop Atamian and Stacey Harmer of the University of California in Davis have upended this theory. They discovered that the flowers are not just responding to light but also to an internal biological clock, according to a report published in the scientific journal Nature. To reach this stunning conclusion, Atamian and Harmer carried out experiments in which sunflower plants grown in fields were shifted into specially made chambers with a fixed overhead light that was always on.

To their surprise, the sunflower carried on as if the sun was rising in the east and setting in the west. The flowers’ faces were moving as if nothing had changed. This continued for several days, according to the Nature report, suggesting that they were not responding only to the direction of the light, but their own timekeeper.

Another discovery presented by Atamian at the annual meeting of the American Society of Plant Biologists in Portland, Oregon, was that the sunflowers bend when one side of the stem grows faster than the other. Faster growth on the west side of the stem, for example, causes the plant to bend towards the east.

The scientists are now studying gene expression on each side of the plant to learn more about how a sunflower’s internal clock can alter growth on one side of the stem but not the other. “Somehow the same clock in the same organ is having opposite effects on opposite sides of the stem,” he was quoted by Nature as saying. “It’s a big open question.”

There are other plants that align themselves to the sun on a daily basis. These include agriculturally important crops such as soybeans, cotton and alfalfa. Scientists have shown that this tracking boosts plant yield. It is also known that mature sunflowers stop tracking the sun and stand straight but facing east, ready to soak up each new sunrise.


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