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Reader question – Wagner J. dos Santos, Campo Grande, MS
The phenomenon responsible for this movement is heliotropism, which only occurs during the plant’s growth phase – when it blooms, it no longer moves. The movement occurs because the side that does not receive light grows faster than the illuminated side, bending the stem towards the light source. Also, a kind of internal clock causes the sunflower to face east during the night. Thus, he already «waits» for the Sun to rise inclined to the right side. According to botanist Heike Hofmann, from the University of Zurich, the movement of the stem and leaves following sunlight serves to facilitate photosynthesis and accumulate energy necessary for seed development. For Rolf Rutishauser, also from the University of Zurich, solar orientation would also attract, because of the heat, pollinating insects, essential for the reproduction of the species.
Consultancy: Luciano Freschi, from the USP Institute of Biosciences, John Sandbakken, director of the National Sunflower Association (USA), Heike Hofmann and Rolf Rutishauser, from the Botanical Institute of the University of Zurich