IAA

Definition

IAA, or indole-3-acetic acid, is a key plant hormone belonging to the auxin class that plays a crucial role in regulating various growth and developmental processes in plants. It influences cell elongation, root formation, and responses to light and gravity, making it essential for plant adaptation and survival. By facilitating these processes, IAA helps plants optimize their growth in response to environmental stimuli.

5 Must Know Facts For Your Next Test

1. IAA is synthesized primarily in the tips of shoots and roots, where it promotes cell elongation and division.
2. In response to light, IAA distribution becomes uneven, causing cells on the darker side to elongate more, resulting in phototropic bending.
3. IAA also plays a significant role in root development, promoting adventitious root formation in certain conditions.
4. The concentration of IAA is critical; too much or too little can result in abnormal growth patterns or developmental issues.
5. IAA regulates apical dominance by inhibiting the growth of lateral buds, allowing the plant to focus resources on vertical growth.

Review Questions

• How does IAA influence phototropism in plants?
  • IAA influences phototropism by causing uneven distribution of the hormone within the plant. When light shines on a plant from one direction, IAA moves to the shaded side, promoting greater elongation of cells on that side. This results in the plant bending toward the light source as the cells on the darker side grow more than those on the lighter side. Thus, IAA is essential for optimizing light absorption for photosynthesis.
• Discuss the role of IAA in root development and how it affects plant adaptation to environmental conditions.
  • IAA plays a crucial role in root development by promoting the formation of adventitious roots and influencing root growth direction. Under certain environmental conditions, such as water availability or soil nutrients, increased IAA concentration can stimulate root branching and elongation. This adaptive response helps plants maximize resource uptake and establish stability in diverse environments, ensuring their survival and growth.
• Evaluate the importance of IAA concentrations in plant growth regulation and how variations can lead to developmental abnormalities.
  • The concentration of IAA is vital for proper plant growth regulation; optimal levels stimulate healthy cell elongation and division. However, variations in IAA concentrations can lead to significant developmental abnormalities. For example, excessive auxin levels can cause uncontrolled cell division resulting in tumorous growths, while insufficient levels may hinder root or shoot development. Understanding this balance is crucial for both natural plant health and agricultural practices.

Related terms

Auxin: A class of plant hormones, including IAA, that regulate growth and developmental processes such as cell division and elongation.

Phototropism:

The growth response of plants toward light, influenced by the distribution of auxins like IAA.

Gravitropism: The directional growth of plant roots and shoots in response to gravity, also regulated by auxins.