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How Sunflowers Follow the Sun's Path: A Circadian Clock Revealed

Sunflower Plants

Story at-a-glance -

  • Sunflower plants are giving scientists a look into how circadian clocks affect not only mammals, but also help control growth in plants
  • Circadian clocks appear to control not only growth, but also increase heat to the plant attracting more pollinating insects, which are important for seed development
  • Sunflower seeds and sprouts pack a powerful punch in your diet and may even help protect your brain and relieve depression

By Dr. Mercola

Sunflower seeds are packed with nutrients, great for snacks and are a tasty addition to your salad. Sunflower plants have also given scientists a peek into the world of how plants use circadian rhythms to improve their growth and ensure propagation.

The sunflower is native to North America but commercialization of the plant took place in Russia.1 Archaeologists believe that sunflowers may have been domesticated by American Indian tribes before corn. Canada started the first official breeding program in 1930.

Although the domesticated plant has only one large flower or head, you may find wild plants throughout North America with multiple heads, sometimes as many as 20 on a plant.2 Most of the sunflowers grown commercially in the U.S. are found in California, Dakotas, Texas, Minnesota, Kansas, Colorado and Nebraska.

Circadian Rhythm Found in Young Sunflower Plants

This short video demonstrates how the sunflower plant follows the sun, and shows the difference between the number of pollinating insects on plants facing east and those facing west.

Circadian clocks play an important role in your health and wellness. Plant biologists from the University of California (UC) discovered the movements of the sunflower plant are triggered by internal hormones, just as your circadian clock is ruled by hormones.

This discovery was a collaboration between molecular biologist Stacey Harmer, Ph.D., from UC-Davis and her colleague, assistant professor Benjamin Blackman, Ph.D., from UC-Berkley. Lead author Harmer told Science Daily:

"It's the first example of a plant's clock modulating growth in a natural environment, and having real repercussions for the plant."3

Under normal circumstances, young sunflower plants appear to orient themselves in response to the sun. In the morning, their flower and leaves are pointed eastward, and as the day passes the leaves gradually move westward.

However, the truly unique movement happens at night, as the leaves return to facing eastward in anticipation of the rising sun. This behavior of the plants has been described as far back as 1898, but has never been associated with circadian rhythms before.

According to this new study, the sunflower uses both heliotropism (the response to sunlight) and circadian rhythm to improve growth performance.4 When staked and unable to move in response to the sun, the plant had less biomass in the stem and less leaf area.5

Staked plants also had fewer visits from pollinating insects. Ann Sylvester, director of the National Sleep Foundation's Plant Genome Research Program, which funded the study, was quoted in the Christian Science Monitor saying:6

"Just like people, plants rely on the daily rhythms of day and night to function. Sunflowers, like solar panel arrays, follow the sun from east to west. These researchers tap into information in the sunflower genome to understand how and why sunflowers track the sun."

The Importance of Pollination

The reduction in visits from pollinators was also an important find. By studying the plants using infrared cameras, the researchers found the plants that started the day facing eastward would warm more quickly than those staked or moved to continue facing westward.7

The warmth attracted five times more insects responsible for pollinating the plants. When the plants that were forced to face westward were warmed with portable heaters, the number of pollinating insects increased to the same level found in the uninterrupted plants.

Production of the sunflower seeds, for which the plant is famous, depends upon pollination. In fact, almost every flowering plant in the world depends upon pollination to produce seeds.

Pollination has a fascinating history but it also plays an essential role in survival of the plant. Bees and other pollinating insects improve the flavor and size of the fruit by providing genetic diversity. In the U.S. alone, the value of pollination for agricultural crops is $10 billion.8

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The Process of 2 Mechanisms Control the Sunflower Plant

Harmer and her team discovered two different mechanisms that appear to control both the movement and the growth of a young sunflower plant as it moves from east to west and back again.

But, not all sunflower plants follow the sun. As the researchers demonstrated, it is only the young plants that move with the sun across the sky. As they mature, the plants continue to face eastward without movement.9

Two mechanisms control plants' movement throughout the day and night. Genes are implicated in the control of growth triggered by light, but not the growth patterns that cause the plant to re-orient during the night hours to face east.10

The researchers found that when the plants faced to the east, the stem on that side grew more rapidly, and the reverse was true at night as the plant turned from west to east.11

The interactions between the environmental responses and the internal circadian clock coordinate the two physiological processes, which scientists can predict. These influence both growth of the plant and reproduction, important to the production of seeds.

Harmer believes there may be two growth processes. Based on available light, the first sets a basic growth rate, while the second is controlled by a circadian clock and influenced by the direction of the light. Harmer, quoted in the Christian Science Monitor, says:12

"A really common misconception is that mature sunflowers follow the sun, actually, they do not. Mature sunflowers always face east. At nighttime, you could see the whole plant rearranging itself, and it was such an amazing thing.

I tell my students all the time that plants are capable of incredible things — we just don't notice because their time scale is different than ours."

Circadian Rhythms Also Affect You

Circadian rhythms or circadian clocks are also important to your health. Just as the plants' rate of growth was stunted when their orientation to the light affected their circadian clock, so is your health negatively affected when hormones and light sources affecting your sleep are changed.

Your circadian rhythms affect you physically, mentally and behaviorally, and roughly follow a 24-hour schedule.13 Your body releases hormones in response to light and dark, affecting your ability to fall asleep and to enjoy quality sleep.  

This internal biological clock regulates your sleepiness and wakefulness throughout the day and night. Adults experience their strongest sleep drive between 2 a.m. and 4 a.m., and in the afternoon between 1 p.m. and 3 p.m. The intensity of sleepiness you experience will depend upon whether you've had sufficient amounts of sleep.14

During the morning hours, when light strikes your optic nerve, the signal travels to your suprachiasmatic nucleus (SCN). This is a group of cells in your hypothalamus that respond to light and dark.

Exposure to light reduces your production of melatonin and increases production of cortisol to wake you up.15 When your circadian rhythm is interrupted it affects several different processes, including the following:

Short term memory

The part of your brain known as the hippocampus must be excited in order for the things you learn to be organized in such a way that you'll remember them later. When your internal clock isn't functioning properly, you release too much GABA, leading to poor short term memory and an inability to retain new information.16

Creativity and learning performance

Proper sleep enhances performance, learning and memory by improving your creative ability to uncover novel connections between seemingly unrelated ideas.

Weight gain/loss

Research has demonstrated that lack of sleep affects levels of metabolic hormones that regulate satiety and hunger, leading to weight gain. When sleep deprived, your body decreases production of leptin, the hormone that tells your brain there is no need for more food. At the same time it increases levels of ghrelin, a hormone that triggers hunger.17

Diabetes and heart disease risk

Both too little and too much sleep may increase your risk of type 2 diabetes. A 15-year study of more than 1,000 men found that those getting less than six or more than eight hours of sleep a night had a significantly increased diabetes risk.18

Immune system

Research has found that when you are well-rested your body may respond to viruses more effectively. Disruption of your circadian clock may also influence cancer progression through changes in hormones like melatonin, which your brain makes during sleep, and which is known to suppress tumor development. When your circadian rhythm is disrupted, your body may produce less melatonin and therefore may have less ability to fight cancer.

Can This Little Seed Protect Your Brain?

The nutrient levels in sunflower seeds pack a big punch. One-quarter cup has a little over 200 calories, and they're an excellent source of vitamin E. The seeds are also high in manganese, copper, vitamins B1, B3 and B6, selenium, phosphorus, magnesium and folate.19

One-quarter cup of seeds provides your body with well over half the amount of copper you need each day. Your body uses copper to maintain skin and hair, to produce melanin and support your body's cells in the production of energy. Maintaining your copper and zinc balance is important to your health and to supporting your immune system. The best way to accomplish this is through the food you eat.

The antioxidant power of vitamin E may help reduce your risk of colon cancer, decrease the frequency and intensity of hot flashes in menopausal women and may help reduce the development of complications from type 2 diabetes.20 High levels of vitamin E are also associated with lower risk of cognitive decline as you grow older.21

Brain protection doesn't end with vitamin E and cognitive decline. Sunflower seeds are also packed with magnesium, known to have a positive effect on your mood. Although the mechanism of action is not well understood, clinical studies dating as far back as 100 years have found health benefits from magnesium.22 Magnesium is a valuable addition to the treatment and prevention of depression.

The Power in the Sprout

Although sunflower seeds are an easy, on-the-go snack, they pack a more powerful punch when sprouted. Growing your own food is fun, satisfying and delicious. Growing sprouts can be done even in small spaces, and doesn't require an outdoor garden.

During sprouting, minerals like magnesium and calcium bind to protein, which makes them more bioavailable. The vitamin and essential fatty acid content of foods also dramatically increase during the sprouting process. Sprouts, like sunflower sprouts, also help extract more of the nutrients — vitamins, minerals, amino acids, and essential fats — from the foods you pair them with. They offer multiple benefits for your body, such as:

  • Support for cell regeneration
  • Alkalizing effect on your body, which helps protect against disease, including cancer
  • Helping protect against abnormal cell growth, viruses and bacteria due to their abundant supply of oxygen (viruses and bacteria cannot survive in an oxygen-rich environment)
  • Providing an abundant and powerful source of antioxidants, enzymes, vitamins and minerals 

Try this delicious recipe at home for a salad that will both surprise you and improve your opinion of healthy foods.

Ingredients Instructions

Ingredients: Salad

1 large head red cabbage, shredded

1 pound spinach

2 cups packed sunflower sprouts

1 bunch fresh cilantro, chopped

1 cup toasted sunflower seeds


1. Preheat oven to 350° F.

2. Place sunflower seeds in a glass dish and place in oven to brown for about 10 minutes.

3. Meanwhile, combine and mix all of the dressing ingredients in a separate bowl.

4. Place the cabbage, spinach, sunflower sprouts and cilantro in a large bowl.

5. Mix with dressing and toasted sunflower seeds.

Ingredients: Dressing

¼ cup apple cider vinegar

¼ cup olive oil

2 tablespoons water

1 tablespoon Dijon mustard

1 garlic clove, pressed

2 tablespoons fresh basil, chopped

Salt and pepper to taste


Serve immediately.

Recipe makes 4 servings.