1. Unequal Distribution of Auxin: When light shines on a coleoptile, a plant hormone called auxin (primarily indole-3-acetic acid or IAA) accumulates on the shaded side of the coleoptile. This uneven distribution is caused by light-induced changes in the movement of auxin within the plant.
2. Cell Elongation: Auxin promotes cell elongation in the growing region of the coleoptile. With more auxin on the shaded side, cells there elongate faster, causing the coleoptile to bend towards the light source.
3. The Role of Photoreceptors: This process is initiated by specialized light-sensitive proteins called photoreceptors in the tip of the coleoptile. These photoreceptors, particularly phototropin 1 and phototropin 2, detect blue light and trigger a signaling cascade that leads to auxin redistribution.
Why is this important?
Phototropism allows seedlings to grow towards light sources, ensuring they receive the optimal amount of light for photosynthesis. This is crucial for their survival and development.
In summary:
* Light triggers auxin accumulation on the shaded side of the coleoptile.
* Auxin promotes cell elongation, leading to bending towards the light.
* This phototropic response allows seedlings to maximize their access to light for photosynthesis.
