Phototropism. Auxins also play a part in phototropism, an occurrence that involves plants bending or moving away from light. ... The extra auxinpresent on the shaded side promotesmore cell division and elongation, causing the plant to bend towards the sunlight after this lop-sided growth.

Introduction:
Phototropism is the growth response of plants towards light. It is primarily regulated by the hormone auxin. Auxin is a plant hormone that plays a crucial role in various aspects of plant growth and development, including phototropism. In this response, we will discuss how auxin promotes phototropism in detail.

Role of Auxin:
Auxin Distribution:
- Auxin is primarily synthesized in the shoot apical meristem and young leaves.
- It moves downwards through the stem towards the roots, primarily in the phloem.
- This polar transport of auxin is facilitated by transport proteins called PIN proteins.
- The movement of auxin towards the shaded side of the plant is called basipetal transport.

Effect of Light:
- When plants are exposed to light, auxin accumulates on the shaded side due to the redirection of auxin transport.
- This unequal distribution of auxin leads to differential growth rates on the shaded and light-exposed sides of the plant.
- The shaded side receives a higher concentration of auxin, promoting cell elongation and growth.

Cell Elongation:
- Auxin stimulates cell elongation by activating proton pumps in the plasma membrane.
- Proton pumps increase the acidity (lower pH) in the cell wall, leading to the loosening of cellulose fibers.
- The loosened cell wall allows water to enter the cell, resulting in turgor pressure and cell elongation.
- As a result, cells on the shaded side elongate more than those on the light-exposed side, causing the plant to bend towards the light source.

Phototropic Bending:
- The differential growth rates between the shaded and light-exposed sides of the plant cause bending towards the light source.
- The elongation of cells on the shaded side results in the curvature of the stem or shoot towards the light.
- This bending response allows the plant to optimize its exposure to light for photosynthesis and growth.

Conclusion:
Auxin plays a crucial role in promoting phototropism by redistributing towards the shaded side of the plant and stimulating cell elongation. This hormone enables the plant to bend towards the light source, optimizing its exposure for photosynthesis and growth. Understanding the mechanisms of auxin-mediated phototropism is essential for studying plant responses to light and developing strategies for improving crop growth and yield.