Name the main groups of plant growth regulators and explain their discovery, physiological functions, and agriculture applications on one of them
The main groups of plant growth regulators are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. In this response, I will focus on auxins.
Discovery: Auxins were discovered in the early 20th century by Charles Darwin and his son Francis, who hypothesized the existence of a chemical messenger that regulates plant growth. However, it was not until the 1930s that the first auxin, indole-3-acetic acid (IAA), was identified and isolated.
Physiological Functions: Auxins play crucial roles in various physiological functions of plants. They are primarily responsible for cell elongation and promoting the growth of lateral and adventitious roots. Auxins also control apical dominance, preventing side branches from growing and promoting the growth of the main stem. Additionally, they aid in phototropism, by causing bending towards light, and gravitropism, by influencing root growth direction.
Agriculture Applications: Auxins have several applications in agriculture, including:
1. Rooting: Auxins are commonly used as rooting hormones to promote root development in cuttings. They stimulate the formation of roots and enhance the chances of successful propagation.
2. Plant Growth Control: Auxins can be used to control unwanted growth in plants. For instance, applying auxin to shoot tips can inhibit lateral bud growth, preventing excessive branching.
3. Fruit Setting: Auxins, such as indole-3-butyric acid (IBA), can assist in fruit setting. Spraying or applying auxins during flowering can increase fruit production by promoting fertilization and preventing premature fruit drop.
4. Weed Control: Synthetic auxins, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are widely used as herbicides to control broadleaf weeds. They selectively target dicot weeds while being less harmful to grasses.
5. Tissue Culture: Auxins are crucial for the development of in vitro plant tissue cultures. They stimulate cell division and growth, aiding in the regeneration of whole plants from small plant parts.
It is important to note that while auxins have significant agriculture applications, their use needs to be carefully regulated and applied at appropriate concentrations to avoid adverse effects on plants or the environment.