Scientists have explained why sunflowers turn towards the sun. Genetics have discovered how a sunflower turns towards the sun. Do sunflowers turn towards the sun?

First, it’s worth clarifying one very important thing. The statement that sunflowers always follow the Sun is true only if we are talking about young, not yet opened sunflower flowers. Contrary to popular belief, mature sunflower flowers do not turn to follow the Sun and usually face east.
Unopened sunflower buds actually follow the Sun, changing their position throughout the day. This phenomenon is called heliotropism (see paragraph at the end of the article).

Observation of the Sun is necessary for sunflowers to grow more efficiently. Scientists fixed the plants, preventing them from turning, or, conversely, rotated the pots, disrupting the natural course of movement. In both cases, the leaves of the plants turned out to be about 10% smaller than those of their neighbors, who calmly turned behind the Sun.

In addition, experts placed several points on the stem with a marker to study how the sunflower moves behind the Sun. Scientists monitored the points using a video camera. If the distance between them changed, it meant that the flower stem was growing where these points were drawn.
When the plants turned to follow the Sun during the day, the eastern side of the stem grew at a faster rate than the western, causing the flower itself to turn toward the Sun. And at night, the western side grew faster, and the stem turned in the other direction.

The secret of sunflower movement lies in the uneven growth of its stem. According to scientists, direct sunlight kills growth hormones contained in the stem, called auxins. The uneven distribution of these hormones along the stem causes the sunflower to grow slower on the sunny side and faster on the shady side, thus tilting the entire stem towards the sun. As the position of the sun changes, the distribution of auxins along the stem also changes, which in turn leads to a change in the inclination of the flower.

Thus, the movement of the plant is carried out with the help of special motor cells that participate in the growth mechanism and are located in the flexible base of the flower. It turned out that this movement depended on the plant's internal clock - circadian rhythms that control various life processes associated with the onset of day, night, morning and evening. The "clock" controls the rate of growth and causes one side of the stem to grow faster than the other. Thanks to this, the sunflower gradually turns to follow the Sun.

As the sunflower matures and the flower opens, overall growth slows and the plants stop moving during the day, remaining oriented to the east. The fact is that the plant reacts more strongly to sunlight early in the morning than in the afternoon, so it gradually stops moving westward during the day.

How do sunflowers move at night?
As we all know, in the morning unopened sunflower buds meet the sun in the east, and in the evening they see it off in the west. Here we could have finished our article, if not for one “but”: in the morning, the sunflower buds are again directed to the east! A completely logical question arises: “how?” Why does the sunflower continue to move at night, without any exposure to the Sun? Moreover, at night the sunflower movements occur at a much higher speed than during the day.
To our general disappointment, scientists cannot yet answer this question with certainty. According to one theory, at night, sunflower cells release the energy that accumulated when the stem tilted, “springing” the flower back. According to another theory, the night movement of the stem does not depend on the sun and is determined by the “internal clock” of the sunflower itself.
Why does an adult sunflower always face east?
As the stem grows and the flower becomes heavier, the redistribution of growth hormones produces an increasingly less noticeable effect. Eventually, the sunflower becomes too heavy to move. Therefore, after ripening, the sunflower no longer follows the Sun and is always directed to the east. But why exactly to the east?
Researchers also do not have an exact answer to this question. Some scientists claim that one night the flower “springs back” to the east and is no longer able to repeat its journey to the west.
Be that as it may, scientists continue to study the sunflower, which unexpectedly for many turned out to be something much more complex than just a flower that constantly follows the Sun.

Heliotropism of flowers
Heliotrope flowers track the movement of the Sun across the sky throughout the day, from east to west. At night, flowers can orient themselves rather haphazardly, but at dawn they turn east, towards the rising luminary. Movement is carried out using special motor cells located in the flexible base of the flower. These cells are ion pumps that deliver potassium ions to nearby tissues, which changes their turgor. The segment bends due to the elongation of the motor cells located on the shadow side (due to an increase in hydrostatic internal pressure). Heliotropism is a plant's response to blue light. One of the most heliotropic flowers is the sunflower, which, more than any other color, “follows” the sun, especially at an early age, until its head grows to a large size and becomes too heavy to move (at this time all its forces are concentrated on the ripening of seeds ). To a greater or lesser extent, almost all flowers are heliotrope.
Some sun-watching plants are not pure heliotropes: their circadian movements are initiated by sunlight, and often continue for some time after its disappearance.
There is a widespread false belief that sunflowers “reach” towards the sun (heliotropism). In fact, mature sunflower flowers usually face east and do not move. However, sunflower buds (before flowering) are heliotropic. They change their orientation from east to west throughout the day.

August 5th, 2016 , 05:59 pm

People have long noticed that young sunflower flowers turn after the Sun during the day, and at night they return to their original position in order to meet it again in the east in the morning. What makes plants perform their daily ritual and why, over time, the “worship” of the luminary stops and mature sunflower flowers do not turn behind the Sun, but remain directed only to the east.

In search of an answer, Stacey Harmer of the University of California, Davis, and her colleagues conducted a series of experiments that confirmed the hunch that observing the Sun is necessary for sunflowers to grow more efficiently. Scientists fixed the plants, preventing them from turning, or, conversely, rotated the pots, disrupting the natural course of movement. In both cases, the leaves of the plants turned out to be about 10% smaller than those of their neighbors, who calmly turned behind the Sun.

In addition, experts placed several points on the stem with a marker to study how the sunflower moves behind the Sun. Scientists monitored the points using a video camera. If the distance between them changed, it meant that the flower stem was growing where these points were drawn.
When the plants turned to follow the Sun during the day, the eastern side of the stem grew at a faster rate than the western, causing the flower itself to turn toward the Sun. And at night, the western side grew faster, and the stem turned in the other direction.

The movement of the plant is carried out with the help of special motor cells that participate in the growth mechanism and are located in the flexible base of the flower. It turned out that this movement depended on the plant's internal clock - circadian rhythms that control various life processes associated with the onset of day, night, morning and evening. The "clock" controls the rate of growth and causes one side of the stem to grow faster than the other. Thanks to this, the sunflower gradually turns to follow the Sun.

As the sunflower matures and the flower opens, overall growth slows and the plants stop moving during the day, remaining oriented to the east. The fact is that the plant reacts more strongly to sunlight early in the morning than in the afternoon, so it gradually stops moving westward during the day.

A long time ago, people noticed that young sunflower flowers turn to follow the sun during the day, and at night they return to their original position to meet it again in the east in the morning. But until now, scientists have not been able to solve this mystery: what makes plants perform their daily ritual and why does the “worship” of the luminary stop over time?

In search of an answer, Stacey Harmer from the University of California at Davis and her colleagues conducted a series of experiments.

At the first stage, conditions were changed for sunflowers growing in their natural environment. Scientists “immobilized” one group so that the plants could not turn at all, and the other was fixed in such a way that the sunflowers at sunrise were turned to the west. When the flowers grew, it turned out that the leaves in both groups were 10% smaller than those of the “free” plants. This confirmed the hunch that observing the sun is necessary for sunflowers to grow more efficiently.

Then the scientists decided to check whether the rhythmic “dancing” of sunflowers was due to internal clocks or environmental conditions.

They moved the plants that were growing outside into a room with constant overhead lighting and found that the sunflowers continued to turn from side to side exactly as they had before for several days.

The scientists then placed the plants in a special room with a string of lamps that turned on one at a time, imitating the movement of the sun. When the researchers programmed artificial lighting on a thirty-hour day/night cycle, the plants turned from side to side without a regular schedule. But when light conditions returned to normal, the sunflowers strictly followed the artificial "sun", showing that internal circadian rhythms play an important role in flower movement.

But most of all, biologists were interested in the question of why, after flowering, sunflowers stop turning from side to side and freeze, “looking” towards the sunrise. Then Harmer's team turned some of the plants to the west, and then counted the number of bees and other pollinators that landed on flowers facing different directions.

It turned out that in the morning, insects visited flowers facing east five times more often than those facing in the opposite direction.

“You can see that bees go crazy for east-facing flowers and pay little attention to west-facing plants,” says Stacy Harmer.

Previous research has shown that pollinators prefer warmer flowers, so sunflowers that receive a large dose of early morning light appear to be more popular.

“I was constantly amazed at how complex plants are,” continues Harmer. “They are truly masterful at adapting to environmental conditions.”

The study, published in Science, raises more complex questions. For example, how do plants tell time and how do they find the right direction when they turn in the dark to where the sun will rise?

But, according to experts, the very fact that sunflowers have an internal clock and are guided by their own rhythms is the “Holy Grail” in the study of their complex behavior. And, as the university press release highlights, this is the first example of temporal synchronization in plants living in natural environments, which has a direct impact on growth efficiency.

Let's add that we previously talked about people who, like people, sleep at night.

Scientists grew several sunflowers, some of them were planted in a laboratory where the lights were constantly on, and others in a regular field, Science reports. Researchers fixed some plants in tubs so that they could not turn behind the Sun.

How a sunflower turns towards the sun

Experts placed several points on the stem with a marker to study how the sunflower moves behind the Sun. Scientists monitored the points using a video camera. If the distance between them changed, it meant that the flower stem was growing where these points were drawn.

It turned out that the movement of the plant depended on its internal clock - a set of light-sensitive proteins and genes “connected” to them, which control various life processes associated with the onset of day, night, morning and evening. The "clock" controls the rate of growth and causes one side of the stem to grow faster than the other. Thanks to this, the sunflower gradually turns after the Sun.

In a laboratory where the length of the day was artificially changed, sunflowers lost the ability to orient themselves towards the Sun, even when the artificial light source moved, like the real star. This negatively affected the speed of flower growth, biomass gain and seed development.

Due to the fact that the sunflower moves behind the Sun, the flower warms up faster and attracts more pollinators, scientists noted.

Let us add that the ability of plants to take a certain position under the influence of sunlight is called heliotropism. Heliotrope flowers track the movement of the Sun across the sky throughout the day, from east to west. At night, flowers can orient themselves rather haphazardly, but at dawn they turn east, towards the rising luminary. To a greater or lesser extent, almost all flowers are heliotrope.

Sunflowers, under the sun.
There is an established opinion that the head of a sunflower turns after the sun.
Yesterday I became convinced that this is a myth.

Below the cut there are recent photos confirming that the sun is shining in the “back of the head” of the sunflower :)
And the real state of affairs

So, as we see, sunflowers do not rotate with the movement of the sun.
But there is some truth in the myth.
Namely, the sunflower looks at the sun at the moment of sunrise.
And he always looks east.
But when the sun goes down, the sunflower does not move behind it.
It's like he's waiting for the next sunrise :)

The phenomenon referred to in the myth is called Heliotropism.
Here's what Wikipedia says about it.
There is a widespread false belief that sunflowers “reach” towards the sun (heliotropism). In fact, mature sunflower flowers usually face east and do not move.
The leaves and buds of young sunflowers exhibit heliotropism. They change their orientation from east to west throughout the day.