Phototropism: How Plants Grow Toward Light

By Priya Sharma · October 14, 2026

The Phototropism Phenomenon

Phototropism is directional growth in response to light. Shoots exhibit positive phototropism (growing toward light), while some roots show negative phototropism (growing away). This ensures leaves maximize light capture for photosynthesis.

The Auxin Mechanism

When light strikes a plant from one side, the hormone auxin (indole-3-acetic acid) redistributes to the shaded side. Higher auxin concentration stimulates cell elongation on that side, causing the stem to bend toward the light source. This was first proposed by the Cholodny-Went hypothesis in the 1920s.

Blue Light Receptors

Phototropins (phot1 and phot2) are the primary blue light receptors mediating phototropism. They are most sensitive to wavelengths around 450 nm. Red and far-red light do not trigger phototropic responses.