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Concept

Phototropism

A young plant with two leaves grows upward under a focused beam of light, demonstrating phototropism, as its roots extend into the soil below.

The growth of a plant toward (or, in roots, away from) light. Blue-light photoreceptors called phototropins detect the light gradient across a stem and redirect the flow of the hormone auxin to the shaded side, causing those cells to elongate faster and bend the shoot toward the source. The mechanism was first inferred by Charles and Francis Darwin in 1880 using oat seedlings.

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