1. Introduction
Plant hormones are small signaling molecules that regulate growth, development, stress responses, and reproductive processes.
Although present in very low concentrations, they exert powerful regulatory control.
Hormones are biochemical signals that coordinate molecular activity with whole-plant performance.
2. Major Classes of Plant Hormones
| Hormone |
Chemical Nature |
Primary Function |
Horticultural Relevance |
| Auxins |
Indole derivatives |
Cell elongation |
Rooting, fruit set |
| Gibberellins |
Diterpenoids |
Stem elongation |
Fruit size regulation |
| Cytokinins |
Adenine derivatives |
Cell division |
Shoot development |
| Ethylene |
Gaseous hydrocarbon |
Ripening |
Postharvest management |
| Abscisic Acid (ABA) |
Terpenoid derivative |
Stress response |
Drought tolerance |
3. Molecular Mode of Action
Plant hormones function by:
- Binding to specific receptors
- Triggering signal transduction pathways
- Altering gene expression
- Modulating enzyme activity
Hormones do not perform metabolism directly — they regulate metabolic pathways.
4. Integration with Primary and Secondary Metabolism
- Auxins influence cell wall modification enzymes.
- Ethylene regulates ripening metabolism.
- ABA activates stress-responsive metabolic pathways.
- Gibberellins stimulate growth-related gene expression.
Hormones connect molecular signals with visible developmental changes.
5. Applied Interpretation in Horticulture
- Rooting hormones improve vegetative propagation.
- Ethylene management controls fruit ripening.
- ABA influences drought response and irrigation strategies.
- Growth regulators improve fruit size and yield uniformity.
Understanding hormone biochemistry allows scientific crop manipulation for productivity and quality.
6. Conceptual Bridge to Later Modules
Hormonal regulation will be studied in greater detail in metabolism and stress modules.
At this stage, the goal is to recognize hormones as molecular coordinators of plant biochemical systems.