Plant Hormones: Definition, Overview, Types, Function, Auxin

What Are Plant Hormones?

Plant hormones are chemical compounds that regulate the developmental, growth, longevity, and reproductive processes of plants. They are produced in almost all parts of a plant and are transmitted into different areas of the plant for action. The hormones may act synergistically or individually, and their roles could be complementary to each other or even antagonistic.

Types Of Plant Hormones

Plant hormones are grouped into two major groups as per their actions: plant growth promoters and plant growth inhibitors.

Plant Growth Promoters

• Auxins: Stimulate cell elongation, apical dominance, and parthenocarpy.

• Gibberellins: Stimulate stem elongation, bolting, and seed germination.

• Cytokinins: Promote cell division, lateral shoot formation, and chloroplast development.

• Ethylene: Triggers fruit ripening, promotes senescence and induces root growth.

Plant Growth Inhibitors

• Abscisic Acid (ABA): Inhibits seed germination, induces senescence, and regulates abscission.

Functions Of Plant Hormones

Each of these plant hormones performs some very specific functions that are quite important to the growth and development of plants.

Auxins

• Indole-3-Acetic Acid, IAA: Promotes cell elongation, apical dominance, and parthenocarpy.

• 2,4-Dichlorophenoxyacetic Acid, 2,4-D: Used as a herbicide that kills dicot weeds.

• Naphthalene Acetic Acid, NAA: Rooting of stem cuttings and grafting.

Gibberellins

• Gibberellins GA1, GA2, GA3: Promotes stem elongation, bolting, and seed germination.

• Breaks Seed Dormancy: It stimulates the formation of hydrolytic enzymes in cereal grains.

Cytokinins

• Zeatin: Induces the growth of lateral and adventitious shoots.

• Kinetin: Induces chloroplast formation and delays leaf senescence.

Ethylene

• Fruit Ripening: Advances fruit ripening.

• Senescence: Induces senescence and abscission of leaves and flowers.

Abscisic Acid (ABA)

• Abscission Inducer: Regulates abscission and dormancy.

• Stress Hormone: Improves plant tolerance to water stress through the induction of stomatal closure.

Role Of Plant Hormones

Plant hormones have a key role in many physiological processes, which include

• Vernalization: The process by which plants require a period of cold temperatures to induce flowering.

• Phototropism: Growth towards light.

• Seed Germination: Transition from dormant seed to active seedling.

• Dormancy: State of inactivity in seed or buds.

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