Phototropic curvature is result of uneven distribution of

Options

A. Auxin
B. Gibberellin
C. Phytochrome
D. Cytokinins

Answer

**Step-by-Step Text Solution:**

1. **Understanding Phototropic Curvature**: Phototropic curvature refers to the bending of plant stems towards light. This phenomenon is crucial for plants as it helps them maximize light absorption for photosynthesis.

2. **Role of Auxin**: Auxin is a plant hormone that plays a significant role in regulating plant growth. It is particularly involved in processes such as cell elongation, which is essential for phototropic responses.

3. **Uneven Distribution of Auxin**: When a plant is exposed to unilateral light (light coming from one direction), auxin is distributed unevenly. The side of the plant that is away from the light receives more auxin, leading to greater cell elongation on that side.

4. **Resulting Curvature**: Because the cells on the shaded side elongate more than those on the light-exposed side, the plant bends towards the light source. This bending is what we refer to as phototropic curvature.

5. **Experimental Evidence**: The Avena coleoptile curvature test is a classic experiment that demonstrates this phenomenon. In this test, the tip of the coleoptile (the part of the plant that senses light) is removed and placed on one side of the cut surface. The plant then bends towards the side where the auxin is concentrated, confirming that auxin is responsible for the phototropic curvature.

6. **Elimination of Other Options**:
- **Zebralin**: This hormone is involved in stem elongation but does not directly influence phototropic curvature.
- **Phytochrome**: This is a pigment that helps plants detect light and is involved in photoperiodism but does not cause curvature.
- **Cytokinin**: This hormone promotes cell division and does not play a role in phototropic responses.

7. **Conclusion**: The correct answer to the question is that phototropic curvature is the result of uneven distribution of auxin.