Have you ever seen a sunflower that orientates to the Sun? They were like moving and following the Sun. Many of us think of plants as fixed creatures that cannot move. However, plants have a limited ability to move. A fascinating member of this realm proves this to us: the Sunflower.
If you have had the opportunity to observe a field of sunflowers, then you must have noticed. These creatures, almost in love with the Sun, follow it constantly. In fact, the people who observed the situation in question gave names such as “sunflower” and “sunlover flower” to this plant.
We can easily turn when we want to change our direction, thanks to our muscles and tendons. Plants do not have such helpers.
So, How Does a Sunflower Move?
An article published in the journal Science in 2016 [ 1] stated that the stems of sunflowers lengthen differently at different times of the day. This results in the tendency of young plants to follow the Sun, called “heliotropism.” Helio means “Sun” in Latin. “ Helium,” the second element in the periodic table, also takes its name from this Latin word.
We observe heliotropism in young sunflowers. During the night, the flexible cells in the western stem of the young sunflower grow faster. As a result of the growth in the west section, that area causes the other side to lose its hardness. Therefore, sunflowers growing on the west side at night are forced to lean to the east.
During the day, the situation is the opposite. The flexible cells on the east side overgrow and suppress the west side, causing that side to tilt. This cycle continues until the plant becomes an adult. That’s why we think that young sunflowers follow the Sun.
In summary, depending on the time of day, one side of the sunflower will grow faster than the other. Because of this growth, the plant tends to bend toward the Sun.
Only Young Sunflowers Follow the Sun!
Sunflower orientation is seen only in young sunflowers, and when the sunflower becomes an adult, the movement stops. This is because the general state of growth of a ripening sunflower, where one side hardens and the other stretches, gradually slows down, just as we humans do. Older plants are positioned to face east, starting to respond more strongly to sunlight earlier in the day. Then, they gradually lose their ability to move.
As a result, the plant’s circadian rhythm makes it respond more strongly to early morning sunlight than to afternoon or evening light. That’s why mature sunflowers don’t follow the Sun and only face east.
Why Do Adult Sunflowers Prefer To Head East?
Two basic ideas have been put forward to explain this situation. The first relates to the increased probability of pollination. Flowers facing the direction of the rising sun get warmer than those facing west. Bees and similar insects, which facilitate pollination, love warm plants. This way, plants that tend to the east get warm and attract more pollinating insects than others.
When the researchers compared mature flowers facing east all day with those facing west, they concluded that stationary flowers attract five times more pollinators. [one]
More sunlight is one of the things a plant desires the most. In this way, it can produce food by doing more photosynthesis.
Okay, Sun orientation has a warming appeal. It also increases the rate of photosynthesis. But is that the only reason? The scientists who asked this question thought that the sun might not be the sole cause and came up with a new idea: the biological clock!
Like humans, plants have biological clocks called circadian rhythms. A person’s circadian rhythm regulates various physiological and chemical changes in his body. For humans, sleeping at night and being awake during the day is an example. An example of the circadian rhythm in young sunflowers is to follow the Sun.
So What Happens If We Tie a Sunflower?
Maybe this question has come to your mind: What happens if we tie a sunflower?
Scientists have prepared a mechanism to answer this question. By tying a sunflower, they restricted its mobility. Thus, its orientation to the Sun did not occur. In some cases, they also distanced the sunflower from the Sun. As a result, they found about a 10% reduction in the plant’s biomass and leaf size. [one]
Now, if you go to the sunflower field near sunset, you can guess how many of these sun-loving plants are young and how many are old!
Reference:
[1] Atamian, H. S., Creux, N. M., Brown, E. A., Garner, A. G., Blackman, B. K., & Harmer, S. L. (2016). Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits. Science, 353(6299),587-590.https://doi.org/10.1126/science.aaf9793
Further Readings:
D’Mello, B. (2022, January 4). Why Do Sunflowers Always Face The Sun? Science ABC. https://www.scienceabc.com/nature/sunflowers-always-face-follow-sun.html
Fell, A. (2016, August 4). How Sunflowers Move to Follow the Sun. UC Berkeley Rausser College of Natural Resources. https://nature.berkeley.edu/news/2016/08/sunflowers-move-clock
Imster, E. (2016, August 17). How sunflowers follow the sun | Earth | EarthSky. EarthSky | Updates on Your Cosmos and World. https://earthsky.org/earth/how-sunflowers-follow-the-sun/
Kennedy, M. (2016, August 6). The Mystery Of Why Sunflowers Turn To Follow The Sun — Solved. NPR.org. https://www.npr.org/sections/thetwo-way/2016/08/05/488891151/the-mystery-of-why-sunflowers-turn-to-follow-the-sun-solved
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