Indole acetic acid (IAA) is a plant hormone that regulates various physiological processes in plants, including growth and development. IAA is synthesized in the shoot apical meristem and transported to various parts of the plant, including the roots.

Inhibition of Root Growth by IAA

IAA generally inhibits the growth of roots. This is because IAA accumulates in the root cap, which is the region at the tip of the root that protects it as it grows through the soil. The accumulation of IAA in the root cap inhibits the growth of the cells in this region, which slows down the growth of the root as a whole.

Mechanism of Action

The inhibition of root growth by IAA is mediated by several mechanisms, including:

1. Inhibition of Cell Division: IAA inhibits the division of cells in the root cap, which slows down the growth of the root.

2. Stimulation of Cell Elongation: IAA stimulates the elongation of cells in the region behind the root cap. This results in the root growing longer but at a slower rate.

3. Alteration of Cell Wall Properties: IAA alters the properties of the cell wall, making it more flexible and allowing the cells to elongate more easily.

Conclusion

In conclusion, IAA generally inhibits the growth of roots by accumulating in the root cap and inhibiting cell division. This slows down the growth of the root as a whole. However, IAA also stimulates the elongation of cells in the region behind the root cap, which allows the root to grow longer but at a slower rate.