To bring all the bees to the yard! These pollinators love warm, bright blooms early in the morning. But how did these plants end up facing east? It turns out they spend their whole life getting in just the right position.
TRANSCRIPT
See how all these sunflowers are facing the same direction?
They’ve been preparing for this moment their entire lives – to be pointing towards the sun just as the bee flies by.
Attracted by the warm, bright blossoms, the bee loads up on pollen and sugary nectar, pollinating the flowers as it goes.
So, how did the sunflowers position themselves so perfectly?
It all started way before the plants even bloomed.
Young sunflower plants start each morning facing east to greet the sunrise.
They follow the sun all day, angling themselves towards it as it travels across the sky.
It’s a behavior called heliotropism, after the Greek word for the sun: helios
More exposure to sunlight means more photosynthesis … and more growth.
When the sun sets, sunflower plants do something curious: They spend all night growing back towards the east, in anticipation of the sun’s return the next morning.
Scientists think the first rays of sun activate a morning crew of genes.
They signal cells on the plant’s east side to swell and elongate faster than those on the west side.
The afternoon genes keep them growing in the same direction.
But then, after sunset, the night shift takes over and signals the cells on the other side to swell, resetting the plant to face east.
Sunflowers follow this rhythm day after day until it becomes a habit.
Researchers at University of California, Berkeley and University of California, Davis took sunflowers grown outside and placed them inside under constant overhead light.
The sunflowers kept up their back-and-forth movement for a few days.
That’s because plants have an internal rhythm called a circadian clock.
We have one too.
Ours tells us when to wake up and when to go to sleep.
Scientists think the sunflowers’ 24-hour clock tells them when and in which direction to grow.
When the plant is ready to bloom, it gives up all that back and forth and fixes itself in place facing east … for the rest of its days.
Why east?
Because bees are out working first thing in the morning. And they like warm, bright flowers lit up by the sun.
So, the flowers need to be in place before the bees arrive.
Researchers found that if they rotated sunflowers to face west they got way fewer visitors.
The bees are after the bright pollen on these tiny things called anthers.
Each sunflower blossom, called an inflorescence, is actually a collection of hundreds or thousands of individual flowers … called florets.
Just before dawn, the plant’s internal clock signals florets at the outside edge to bloom.
They push pollen from deep inside, out to the tips.
Later in the day, another part called the style extends up and out of the floret.
Its end splits open, ready to receive pollen from other plants.
This is why the bees are so essential.
As they fly from flower to flower, they move pollen into those curled-back styles.
Each pollinated floret grows into a seed.
When all the florets have blossomed, the sunflower hangs its head and dries out.
Those seeds aren’t just a snack. They’re an important source of cooking oil grown in huge quantities.
And growers are always breeding new varieties to maximize their yield. But sometimes they accidentally mess with the sunflower’s biological clock, and throw it out of sync with the sunrise.
By learning what makes sunflowers tick, researchers want to ensure new varieties show up right on time.
Before you go we want to tell you about “Weathered: Earth’s Extremes.” If you’re familiar with the YouTube series on PBS Terra, you’ll be excited to know that it’s expanding into a TV miniseries which tells the definitive story about our changing weather and climate. Link in the description