UC Davis study: Sunflowers move by the clock

UC Davis study: Sunflowers move by the clock

UC Davis study: Sunflowers move by the clock

The burning question - why sunflowers all the time follow the sun - has an answer.

Though sunflowers are known for their uncanny ability to follow the sun as it moves across the sky, how or why they track the star has always been a mystery.

Scientists as far back as 1898 had described this behavior of sunflowers, but no one had thought to associate it with circadian rhythms. The handsome yellow flowers turn east in the morning to face the rising sun and then moves across the sky during the day before heading westward by dusk.

Next, the researchers created an artificial "daylight" cycle with the artificial light by turning a light on in the east in the mornings, and then in the west in the evenings.

It's summertime, and fields are colored with an array of flowering plants - some of them sunflowers - that are dutifully watching the rising sun. Growth rates on the east side are highest during the day, and lowest at night, and on the west side the reverse is true. At night, the west sides grew faster as the stems swung the other way. First, they forcibly would stop plants from turning or would plant them in areas without direct sunlight and found that plants deprived of the sun would have less mass and less leaf area than those that could grow uninhibited.

However, a new study published on Friday in Science by a team at UC Davis reveals some of the secrets behind the plant's movement, and it comes down to circadian rhythm.

Plant biologists have long documented the remarkable ability of sunflowers and other plants to follow the sun.

A report published in LA Times informed, "In another lab experiment, the researchers messed with the sunflowers' internal clocks by exposing them to a 30-hour light cycle". The same occurs at night for the cells on the western section of the stem, allowing the plant to point towards the east and face the sun as it rises on the horizon. "Mature sunflowers always face east". "I tell my students all the time that plants are capable of incredible things - we just don't notice because their time scale is different than ours", Harmer said in a statement.

He conducted his research supported by a National Science Foundation grant from the Plant Genome Research Program at a field site at UVA's Morven Farm, along with former Harrison Undergraduate Research Scholar Evan Brown, a 2014 UVA alumnus.

Researchers also found that sunflowers that were heated by the sun attracted more insects. "It's the first example of a plant's clock modulating growth in a natural environment, and having real repercussions for the plant". However, senior author Stacey Harmer from UC Davis wanted to know the link of these clock genes with a hormone called auxin that control stem growth.

In order to complete their study, the team planted a field of sunflowers with each in their own pot so that variables could be brought into the mix easier.

As the sunflower matures and the flower opens up, overall growth slows down and the plants stop moving during the day and settle down facing east. The east-facing plants warmed up more quickly than their west-facing counterparts, which could account for some of the difference, given that warmer flowers have previously been found to attract more pollinators.

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