What are plant hormones? Name a plant hormone that promotes growth in plants.

Plant hormones, also known as phytohormones, are chemical messengers that regulate various physiological processes in plants. These hormones play a crucial role in coordinating growth, development, and responses to environmental stimuli. Each plant hormone has specific functions, and they often interact in complex ways to control plant growth and behavior.

One plant hormone that promotes growth in plants is auxin. Auxins are involved in several aspects of plant growth, including cell elongation, root development, and the formation of lateral roots. They are produced in the shoot apical meristem (growing tips of stems and roots) and move downward through the plant.

One well-known synthetic auxin is indole-3-acetic acid (IAA), which is often used in research and horticulture. Auxins are responsible for the following growth-related activities:

1. Cell Elongation: Auxins promote cell elongation by increasing the plasticity of the cell wall. This is crucial for the growth of stems and roots.

2. Apical Dominance: Auxins inhibit the growth of lateral buds, promoting the dominance of the apical (top) bud. This ensures that the plant directs its energy toward upward growth.

3. Root Development: Auxins stimulate the initiation and elongation of roots. They are often used as rooting hormones in horticulture to promote the development of roots in cuttings.

4. Phototropism: Auxins are involved in phototropism, the bending of plant parts toward light. They accumulate on the shaded side of the stem, causing cells to elongate more on that side and bending the stem toward the light source.

5. Gravitropism: Auxins also play a role in gravitropism, the response of plant parts to gravity. In roots, auxins accumulate on the lower side, inhibiting cell elongation and causing the root to grow downward.

It’s important to note that plant growth is a highly coordinated process involving the interplay of multiple hormones, including auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Each hormone has specific functions, and their concentrations and interactions determine the overall growth and development of the plant.