Phototropism

Phototropism is directional plant growth in response to light. Shoots commonly bend toward light because growth is redistributed across the two sides of a stem.

Phototropin: A blue-light receptor protein that regulates plant responses, including phototropism. Phototropins detect directional blue light and initiate signaling that redirects shoot growth.
Tropism: Directional growth of an organism or organ in response to a directional stimulus. Phototropism is the light-directed instance of this broader class of growth responses.
Gravitropism: Directional plant growth in response to gravity. Gravity directs growth in this tropism, whereas directional light drives phototropism.
Canary grass: A group of grasses whose seedlings have been used in experiments on plant growth and light responses. Darwin and Francis Darwin used grass seedlings to investigate how shoot tips sense light.
Auxin: A plant hormone that regulates growth and development, including cell elongation. Auxin becomes unevenly distributed across illuminated shoots, producing unequal growth.
Plant hormone: A signaling molecule that regulates plant growth and development at low concentrations. Auxin acts as the hormonal signal underlying much phototropic bending.
Phototaxis: Directional movement of a motile organism toward or away from light. Phototaxis changes an organism’s position through movement, not growth-driven bending.
Charles Darwin: An English naturalist who developed the theory of evolution by natural selection. His seedling experiments helped establish that the shoot tip perceives light during phototropism.
Cholodny–Went model: A model proposing that tropic curvature results from unequal hormone distribution and growth across an organ. It explains phototropic bending through greater auxin-driven elongation on a shoot’s shaded side.
Plant cell elongation: An increase in a plant cell’s length through cell-wall expansion and water uptake. Unequal elongation of cells across a shoot creates its visible curvature.

Linked from 13 pages