How does auxin promote phototropism?

Auxin promotes phototropism, the directional growth of plants in response to light, through a process called asymmetric auxin distribution. Here's how it works:

Initial Perception of Light: When light hits a plant, it's perceived by photoreceptors, primarily phototropins and cryptochromes, located in the plant's cells. These photoreceptors are most sensitive to blue light.
Activation of Signal Transduction Pathway: Upon light perception, these photoreceptors trigger a signal transduction pathway that ultimately leads to the redistribution of auxin.
Asymmetric Distribution of Auxin: In response to light, auxin accumulates on the shaded side of the stem or organ. This creates an asymmetric distribution of auxin, with higher levels on the shaded side compared to the illuminated side.
Cell Elongation and Growth: Auxin, particularly indole-3-acetic acid (IAA), promotes cell elongation and growth. When auxin accumulates more on one side of the stem or organ, it induces greater cell elongation and growth on that side, causing the plant to bend towards the light source.
Resulting Phototropic Response: The differential growth between the shaded and illuminated sides of the plant leads to bending towards the light, allowing the plant to maximize light capture for photosynthesis.
Overall, auxin acts as a key mediator in translating the perception of light into a growth response, leading to phototropism in plants.