Always turning towards the sun. Scientists have explained the mechanism and purpose of sunflower turns behind the sun. Scientists explain that the movement of the sunflower inflorescence occurs due to the uneven growth of the plant. One side of the stem grows faster than the other
August 5th, 2016 05:59 pm
For a long time, people have 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 him 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 after 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 sunflowers need to observe the Sun 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 the neighbors, who calmly turned after the Sun.
In addition, experts put several dots on the stem with a marker to study how the sunflower moves behind the Sun. The scientists monitored the dots with a video camera. If the distance between them changed, this meant that the flower stem grew where these points were drawn.
When the plants turned to follow the Sun during the day, the eastern side of the stem grew faster than the western side, causing the flower itself to turn towards the Sun. And at night, the western side grew faster, and the stem turned the other way.
The movement of the plant is carried out with the help of special motor cells involved in the growth mechanism and located in the flexible base of the flower. It turned out that this movement depended on the internal clock of the plant - 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. Due to this, the sunflower gradually turns after the Sun.
As the sunflower matures and the flower opens, the overall growth slows down and the plants stop moving during the day, remaining oriented to the east. The fact is that the plant reacts more strongly to sunlight in the early morning than in the afternoon, so it gradually stops moving to the west during the day.
A long time ago, people noticed that young sunflower flowers during the day turn after the sun, and at night they return to their original position in order to meet him again in the east in the morning. But until now, scientists could not solve this riddle: 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 of 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 sunflowers turned west at sunrise. When the flowers grew up, it turned out that the leaves in both groups were 10% smaller than in the "free" plants. This confirmed the hunch that sun exposure is necessary for sunflowers to grow more efficiently.
Then the scientists decided to check what caused the rhythmic "dances" of sunflowers - the internal clock or environmental conditions.
They moved plants growing outdoors into a room with constant overhead lighting and found that the sunflowers continued to turn from side to side for several days, just as they did before.
The scientists then placed the plants in a special room with a string of lamps that turned on in turn, simulating the movement of the sun. When the researchers programmed the artificial lighting to a thirty-hour "day" and "night" cycle, the plants turned from side to side without a regular schedule. But when the light regime returned to normal, the sunflowers strictly followed the artificial "sun", showing that internal circadian rhythms play an important role in the movement of the flower.
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 the Harmer team turned part of the plants to the west, and then counted the number of bees and other pollinators that landed on flowers facing different parts of the world.
It turned out that in the morning hours, insects visited flowers facing east five times more often than those turned in the opposite direction.
"You can see that the bees just go crazy for east-facing flowers and hardly pay attention to west-facing plants," notes Stacey Harmer.
Previous research has shown that pollinators prefer warmer flowers, so sunflowers that receive a higher dose of early morning rays are more popular.
"I've always been amazed at how complex plants are," continues Harmer. "They're really adept at adapting to their environment."
The results of the study, published in Science, raise 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 studying their complex behavior. And, as emphasized in a press release from the university, this is the first example of time synchronization in plants living in the natural environment, which has a direct impact on growth efficiency.
Material. Te material expansion difference due to temperature. More sun than shade. As far as I know, the base of the head at the point of attachment of the stem looks like "hard cotton wool" with liquid. Maybe this fluid in the pores plays the role of muscles - are there hydraulics?
[email protected] 01.08.2011
VIVAT - GOOGLE!
Name: comes from a combination of two Greek words "helios" - the sun and "anthos" - a flower. This name was given to him for a reason. Huge sunflower inflorescences, bordered by bright radiant petals, really resemble the sun. In addition, this plant has the unique ability to turn its head following the sun, tracing its entire path from sunrise to sunset.
Plants do not have muscles, the flower can change orientation only due to the fact that the stem that holds it grows stronger on the sunny side. Therefore, the process takes place when the sunflower grows: during the day, closed flowers really follow the course of the sun, justifying their French name tournesol. 
An even more amazing trick: during the night, the flowers manage to turn so that in the morning they again greet the sun in the east.
Thanks to this rotation, plants in the growth phase manage to catch 10-15 percent more solar energy. A grown sunflower with an open flower looks motionlessly to the east.
The section of the stem under the petals of a flower contains<гормон роста>. This hormone cannot withstand direct sunlight. Once in the sun, this part of the stem turns so as to get away from it. It concentrates<гормон роста>, so it grows faster, and as a result, the flower itself turns towards the sun.
So I was thinking in the right direction, I just could not imagine that a plant could grow so quickly. Thanks to Google, I somehow didn’t think of googling this question. But beautiful pictures appeared in the topic. Do you know that in Germany it is customary to make bouquets of sunflower flowers? For your birthday, you may well be presented with such a bouquet.
Alexey.n.pop***@u*****.ua Teacher 03.08.2011
Thanks Google! Nothing is clear - the expediency of this movement is simply indicated, but what mechanism? And why does the rotation occur at night - does it mean there is memory or celestial navigation?
It's a delusion. He does not turn FOLLOWING THE SUN. It is constantly directed in that direction, the average daily brightness of which is the greatest ... Just like the leaves of cucumbers in a greenhouse, just like indoor flowers on the windowsill.
Take a closer look. And early in the morning, at dawn, and late in the evening at sunset in an open field, the sunflower heads will be directed to the South. And in the shaded area - away from the shadow falling on it.
To begin with, it is 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 follow the Sun and are usually eastward.
Unopened sunflower buds really follow the Sun, changing their position during the day. This phenomenon is called heliotropism (see paragraph at the end of the article).
Sunwatching is essential 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 the neighbors, who calmly turned after the Sun.
In addition, experts put several dots on the stem with a marker to study how the sunflower moves behind the Sun. The scientists monitored the dots with a video camera. If the distance between them changed, this meant that the flower stem grew where these points were drawn.
When the plants turned to follow the Sun during the day, the eastern side of the stem grew faster than the western side, causing the flower itself to turn towards the Sun. And at night, the western side grew faster, and the stem turned the other way.
The secret of sunflower movement lies in the uneven growth of its stem. According to scientists, direct sunlight kills the growth hormones contained in the stem, which are 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 shade side, thus tilting the entire stem towards the sun. With a change in the position of the sun, the distribution of auxins along the stem also changes, which in turn leads to a change in the slope of the flower.
Thus, the movement of the plant is carried out with the help of special motor cells involved in the growth mechanism and located in the flexible base of the flower. It turned out that this movement depended on the internal clock of the plant - 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. Due to this, the sunflower gradually turns after the Sun.
As the sunflower matures and the flower opens, the overall growth slows down and the plants stop moving during the day, remaining oriented to the east. The fact is that the plant reacts more strongly to sunlight in the early morning than in the afternoon, so it gradually stops moving to the west during the day.
How do sunflowers move at night?
As we all know, unopened sunflower buds meet the sun in the east in the morning and see it off in the west in the evening. Here we could finish our article, if not for one "but": in the morning, sunflower buds are again directed to the east! A logical question arises: “how?” Why does the sunflower keep moving at night, without any influence from the sun? Moreover, at night, sunflower movements occur at a much higher speed than during the day.
To our dismay, scientists cannot yet answer this question with certainty. According to one theory, at night the cells of a sunflower release the energy that has accumulated when the stem is tilted, "springing" the flower back. According to another theory, the night movement of the stem does not depend on the sun and is due to the “internal clock” of the sunflower itself.
Why does an adult sunflower always face east?
With the growth of the stem and the weight of the flower, the redistribution of growth hormones has a less and less noticeable effect. Eventually, the sunflower flower becomes too heavy to move. Therefore, after ripening, the sunflower no longer follows the Sun and always points to the east. But why east?
Researchers also do not have an exact answer to this question. Some scholars argue that one night the flower "springs" 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 during the day, from east to west. At night, flowers can orient themselves rather haphazardly, but at dawn they turn east, towards the rising sun. Movement is carried out with the help of 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 elongation of the motor cells located on the shadow side (due to the increase in hydrostatic internal pressure). Heliotropism is the plant's response to blue light. One of the most heliotropic flowers is the sunflower, which follows the sun most of the other flowers, especially at an early age, until its head grows to a large size and becomes too heavy to move (at which time all its forces are concentrated on the ripening of seeds ). To a greater or lesser extent, almost all flowers are heliotropic.
Some sun-following plants are not pure heliotropes: their circadian movements are initiated by sunlight, and often continue for some time after it has disappeared.
There is a widespread misconception that sunflowers "stretch" towards the sun (heliotropism). In fact, mature sunflower flowers usually point east and do not move. However, sunflower buds (before flowering) have heliotropism. They change their orientation from east to west during the day.
Sunflowers, under the sun.
There is a well-established opinion that the head of a sunflower turns after the sun.
Yesterday I was convinced that this is a myth.
Under the cut there are fresh photos confirming that the sun shines in the "back of the head" of a sunflower :)
And the real state of affairs
So as we can 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 to the east.
But when the sun goes down, the sunflower does not follow it.
It's like 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 misconception that sunflowers "stretch" towards the sun (heliotropism)] . In fact, mature sunflower flowers usually point east and do not move.
The leaves and buds of young sunflowers are heliotropic. They change their orientation from east to west during the day.