The sunflower disk rotates with the sun, it turns out that this part is afraid of light!

Review expert: Wang Kang, Director of the Science Museum of the National Botanical Garden, Senior Engineer

Wearing a flower hat, he looks so handsome, standing in the field, smiling at the sun. If you use the above riddle to guess a plant, I believe everyone will blurt out without hesitation: sunflower.

Sunflower, also known as sunflower and sunflower, is a beautiful and vital plant. The most prominent label attached to it is "smiling at the sun".

A long time ago, people discovered that the sunflower disk rotates with the movement of the sun . This feature is also the origin of the name "sunflower".

So why do sunflowers revolve around the sun? What scientific principle is behind this?

"Smile at the Sun"

It's actually a survival strategy

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The fact that the sunflowers revolve around the sun is related to the basic characteristics of their growth. The sunflower is a typical sun-loving plant that has a strong demand for light. During the growth process, the stems of the sunflowers will continue to grow taller and the flower disk will also increase accordingly to better receive sunlight. At night, the sunflowers will readjust their leaves and young flower disks and face east again to wait for the sunrise.

The rotation of the flower disk is a survival strategy adopted by sunflowers to maximize the amount of sunlight they receive.

Uncover the sunflower

The Secret of Following the Sun

This is mainly due to a special auxin in the stem of the sunflower, which can make the plant grow tall and big, but it is timid and afraid of light . Therefore, when the auxin in the neck of the sunflower sees the sun, it runs to the side that is not lit and hides. The auxin on the side that is not lit becomes more and more, which makes this side grow particularly fast, while the side facing the sun grows slower because of less auxin. The two sides of the stem grow at different speeds, and the side that grows faster will bend toward the side that grows slower , so that the flower disk faces the light source.

With the improvement of science and technology, scientists have discovered that in addition to the difference in auxin concentration on both sides of the growth zone at the end of the sunflower stem, there is also a difference in the concentration of growth inhibitors . This inhibitory substance is called flavonoids , which, in contrast to auxin, inhibits cell elongation and accumulates on the sunny side, causing the two sides of the stem to grow at different rates. Therefore, the uneven distribution of flavonoids also prompts the plant to rotate toward the light.

In addition, the "biological clock hypothesis" can also explain why sunflowers move towards the sun. The "biological clock" allows animals and plants to know what they should do at a certain time of the day. The "endogenous hypothesis" of biological rhythms is widely recognized. It believes that the physiological rhythms of most existing organisms are actively changed endogenously regulated by the timing mechanism in the body . Biological rhythms are relatively stable to periodic changes in the environment.

Studies have found that even on cloudy days when the sun is not obvious, sunflowers will follow the sun and rotate from east to west. At night, they will move their flower disks back to the east to wait for the sunrise of the new day. This is probably the result of the biological clock.

△The sunflower stem ends with different growth rates on both sides. Source: Baidu Pictures

It is the combined effect of the above factors that allows us to see the sunflower disk constantly adjusting its direction with the changes in the sun, turning from east to west every day.

What does the phenomenon of sunflowers orbiting the sun mean to the plants themselves?

1. By adjusting the direction of the flower disk, the sunflower can ensure that every part of the flower disk can fully receive sunlight, thereby improving the efficiency of photosynthesis and promoting the growth and development of the plant.

2. This rotation helps the sunflowers avoid having their stems burned by strong sunlight and protects the normal growth of the plants.

Stop turning your head.

Why do sunflowers face southeast?

It is worth noting that sunflowers do not revolve around the sun throughout their growth cycle. When the flower disk matures and begins to produce seeds, the stem of the sunflower gradually becomes hard and can no longer bend. At this time, the sunflower disk will maintain a fixed direction, roughly facing southeast , and no longer move with the sun.

So why do sunflowers always face southeast? This is probably the result of natural selection.

1. The flower disk is facing the sun, which helps to dry the dew condensed at night and reduce the chance of fungal infection .

2. When the temperature is lower in the morning, direct sunlight can raise the temperature of the sunflower disk, forming a warm small space, thereby attracting insects to stay there and help with pollination .

△Bees are collecting sunflower pollen. Source: Inner Mongolia Agriculture and Animal Husbandry Department

3. The sunflower disk should face southeast to avoid direct sunlight at noon and prevent high temperatures from burning the pollen.

In short, the phenomenon of sunflowers revolving around the sun is a magical ability given to plants by nature. Because of the bend of the stem, the sunflower can sense and follow the sun, thereby maximizing the amount of sunlight it receives, improving the efficiency of photosynthesis, and promoting its own growth and development. This phenomenon not only demonstrates the wonders of nature, but also provides us with valuable clues for studying the mechanisms of plant growth and adaptation to the environment.