Phytohormones are signalling chemicals produced by plants (i.e. plant hormones) to regulate growth and developmental processes

• Changing the concentrations and distributions of phytohormones allows plants to differentially respond to external and internal stimuli

Examples of phytohormones include:

• Auxins – Promotes both primary growth and directional growth responses (tropisms)

• Cytokinins – Promotes cell division to help regulate primary and secondary growth

• Ethylene – Responsible for the ripening and longevity of fruit

• Gibberellins – Triggers germination in dormant seeds

• Abscisic Acid – Responsible for leaf shedding (abscission) and stomatal closure

Phytohormone Responses