Plant Hormone Notes
What are these compounds?
- Plant hormones
- natural, organic plant growth substances transported within the plant in low concentrations that regulate plant physiological processes.
- Plant Growth Regulators (PGR)
- Synthetic or natural compounds that regulate plant physiological processes such as growth and development.
Growth Promoting Hormones
- Stimulate cell elongation and are used to stimulate initiation of adventurous roots on cuttings. Examples: Indole-3-acetic acid (IAA) Jmol
- Stimulate cell elongation also important in seed germination. Example: GA3 Jmol
- Stimulate cell division and are important in shoot initiation and branching.
- Promote cell elongation in stems.
- Stimulates swelling of roots and stems. Used to promote ripening of fruit. Jmol
- Abscisic acid (ABA)
- Inhibits growth to promote survival. Jmol
A Note on Concentrations
Hormones are present in very minute concentrations. PGRs are also applied in very low concentrations. High concentrations can act as herbicides (2,4-D)
- One part per million (1 ppm) is equivalent to 1 mg of material in 1 liter of solution
- 1% = 10,000 ppm
- 1 ppm ≈ 1 teaspoon in 4 hot tubs (5ml in 5000l).
Reference: The Biology of Horticulture. Preece, John E. 2005. John Wiley & Sons.