PerspectivePlant Science

How do sunflowers follow the Sun—and to what end?

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Science  05 Aug 2016:
Vol. 353, Issue 6299, pp. 541-542
DOI: 10.1126/science.aah4439

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A field of domesticated sunflowers (Helianthus annuus) fully in bloom is a striking sight. The large and showy flowering heads face east, positioned toward the rising Sun. Before floral development, however, elongating vegetative stems move their apices steadily from facing east in the morning to facing west in the afternoon, following the Sun—a process known as solar tracking or heliotropism (1). During the night, the shoots reorient their apices to face east again at sunrise (see the figure). As flower development is initiated, solar tracking diminishes and finally ceases, with the developing flowering heads at rest and facing east. On page 587 of this issue, Atamian et al. (2) provide mechanistic insights into this tracking phenomenon and postulate an evolutionary link to pollination.