Helianthus’ heliotropism explained. A new study has discovered what causes sunflowers to turn their heads so they all face the same direction. Known as heliotropism, sunflowers aren’t the only plants that track the sun but until now, how sunflowers do it has been a mystery.
Wanting to know why sunflowers rotate, a team of researchers from the University of California, Davis, looked at whether the flowers were following the sun or following an internal cue. By putting the sunflowers indoors with lighting that mimicked the sun’s path, they discovered over 24 hours they behaved ‘normally’ but over 30 hours they were confused and their pattern altered, meaning they were following something internal rather than the light.
The researchers found that genes in young sunflowers click on during the day to cause the east-facing half of the stem to grow. The lengthening stem causes the flower head to slowly bend to the west during the day. At night, genes that cause the west-facing part of the stem to grow activate, causing the head to turn back to the east.
This circadian regulation continues until the flowers age, at which point it stops and the flowers stop turning. They are then always facing east. The researchers also discovered that east-facing flowers heat up more quickly than west-facing ones, and as a result attract five times as many pollinators. This supports previous studies that believed pollinators prefer warm flowers in the morning.
Of course the exact complexities of how this all works and fits together are still unknown, and hopefully the topic of further scientific study.
Sources: www.smithsonianmag.com, www.sciencemag.org, www.nytimes.com