Young sunflowers, as you may have observed, are heliotropic and appear to follow the sun (cue The Beatles!). However, mature sunflowers continue to face east once the stalk has matured to gather maximum warmth and pollinators (cue the Beetles!).
Young sunflowers (Helianthus annuus) grow better when they track the sun’s daily motion from east to west across the sky. An internal clock helps control the behavior, Dr. Stacey Harmer and researchers report in 8/5/16 issue of Science.
Depending on the time of day, certain growth genes appear to be activated to different degrees on opposing sides of young sunflowers’ stems. The east side of their stems grow faster during the day, causing the stems to gradually bend from east to west. The west side grows faster at night, reorienting the plants to prepare them for the next morning. “At dawn, they’re already facing east again,” says Harmer, University of California, Davis. The behavior helped sunflowers grow bigger.
Young plants continued to grow from east to west each day even when their light source didn’t move. So Harmer and her colleagues concluded that the behavior was influenced by an internal clock like the one that controls human sleep/wake cycles, instead of being solely in response to available light.
That’s probably advantageous, Harmer says, “because you have a system that’s set up to run even if the environment changes transiently.” A cloudy morning doesn’t stop the plants from tracking the sun, for instance.
Contrary to popular belief, mature sunflowers don’t track the sun — they perpetually face east. That’s probably because their stems have stopped growing. But Harmer and her colleagues found an advantage for the fixed orientation, too: Eastern-facing heads get warmer in the sun than westward-facing ones and attract more insects.
I was happy to find a sunny topic for this week's PEOTS. This one is for Zoë.
Sunnily,
Steph
Young sunflowers (Helianthus annuus) grow better when they track the sun’s daily motion from east to west across the sky. An internal clock helps control the behavior, Dr. Stacey Harmer and researchers report in 8/5/16 issue of Science.
Depending on the time of day, certain growth genes appear to be activated to different degrees on opposing sides of young sunflowers’ stems. The east side of their stems grow faster during the day, causing the stems to gradually bend from east to west. The west side grows faster at night, reorienting the plants to prepare them for the next morning. “At dawn, they’re already facing east again,” says Harmer, University of California, Davis. The behavior helped sunflowers grow bigger.
Young plants continued to grow from east to west each day even when their light source didn’t move. So Harmer and her colleagues concluded that the behavior was influenced by an internal clock like the one that controls human sleep/wake cycles, instead of being solely in response to available light.
That’s probably advantageous, Harmer says, “because you have a system that’s set up to run even if the environment changes transiently.” A cloudy morning doesn’t stop the plants from tracking the sun, for instance.
Contrary to popular belief, mature sunflowers don’t track the sun — they perpetually face east. That’s probably because their stems have stopped growing. But Harmer and her colleagues found an advantage for the fixed orientation, too: Eastern-facing heads get warmer in the sun than westward-facing ones and attract more insects.
I was happy to find a sunny topic for this week's PEOTS. This one is for Zoë.
Sunnily,
Steph
