Dancing Sunflowers: New Study unveils How yellow-headed Plants Trace Sun’s Movement

All of this might sound pretty obvious for gardeners who’ve been watching their sunflowers shift throughout the day for years, but it’s the first time scientists have been able to link gene expression with the behaviour of a plant in the field. And why does the sunflower, once mature, face east regardless of the sun’s orientation?

Experts have countered a red-hot question dominant to the attraction of sunflowers: Why do fledgling flowers move their blossoms to always face the sun over the way of a day?

So, in the mornings, the researchers found that certain genes were being expressed at higher levels on the east side of the plant’s stem, and in the afternoon, this pattern switched.

Study’s lead researcher Stacey Harmer from University of California-Davis informed that they carried out an experiment in which they first staked the sunflowers so they are unable to move.

The study suggests that the process of the sunflower turning takes place when different sides of the flower’s stem elongate, depending on the time of day. The constrained, frail flowers were then moved to an indoor growth chamber, where the sunflowers swang back and forth even without a direct response to the sun.

“The higher growth rate on the east versus west side of the stem during the day enables the shoot apex to move gradually from east to west”, the researchers added in the official press statement from UC Davis.

To see if the plants had their own biological clocks that were reset daily by the Sun, similar to our own, or were simply moving according to a pre-determined schedule, the team performed a series of experiments. The heads of young sunflower plants – those with immature flowers – follow the sun during the day, then reverse course at night, so they’re ready to face the dawn.

“Just like people, plants rely on the daily rhythms of day and night to function”, said the director of the National Science Foundation’s Plant Genome Research Program, Anne Sylvester.

By staking plants so that they can not move, or turning potted plants around daily so that they were facing the wrong way, they disrupted the ability of the plants to track the sun.

Another phase of experimentation had the flowers isolated in an indoor growth environment with a single overhead light, directly above the plant.

Why do mature sunflowers face east?

That means there are two growth mechanisms at work in the flower’s stem, the researchers said. First, there is the basic growth rate, which is based on how much light is available. This behavior of sunflowers had been described by scientists as far back as 1898, but no one had previously thought to associate it with circadian rhythms. Second, the internal clock is set to track the direction of light, leading the stem to grow unevenly, and causing the sunflower to sway east and west throughout the day. As a result, the plants grew smaller than those that followed the sun. A portable heater was enough to restore a large numbers of pollinators back to the west-facing ones.

It was also determined that sunflowers facing the sun become heated more quickly, which in turn attracts a larger amount of insects, promoting pollination.

“Bees”, said Harmer, “like warm flowers”.