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

Auxins
Stimulate cell elongation and are used to stimulate initiation of adventurous roots on cuttings. Examples: Indole-3-acetic acid (IAA) Jmol external arrow
Gibberellins
Stimulate cell elongation also important in seed germination. Example: GA3 Jmol external arrow
Cytokinins
Stimulate cell division and are important in shoot initiation and branching.
Brassinosteroids
Promote cell elongation in stems.

Stress Hormones

Ethylene
Stimulates swelling of roots and stems. Used to promote ripening of fruit. Jmol external arrow
Abscisic acid (ABA)
Inhibits growth to promote survival. Jmol external arrow

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)


Reference: The Biology of Horticulture. Preece, John E. 2005. John Wiley & Sons.