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Sunflowers Have Internal Clocks?

By Wochit 04 August 2016

Young sunflowers grow better when they track the sun’s daily motion from east to west across the sky. An internal clock helps control the behavior, biologist Stacey Harmer and colleagues report. 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. 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.