Plant hormone

Plant Hormone

Auxin, a key plant hormone.

Plant hormones, also known as phytohormones, are naturally occurring organic compounds that play crucial roles in regulating the growth, development, and responses of plants. These hormones are produced in small quantities and can have significant effects on plant physiology.

Types of Plant Hormones

Plant hormones are classified into several major groups, each with distinct functions and effects on plant growth and development.

Auxins

File:Indol-3-ylacetic acid.svg

Chemical structure of Indole-3-acetic acid, a common auxin.

Auxins are a class of plant hormones that primarily regulate cell elongation, apical dominance, and root initiation. The most common naturally occurring auxin is Indole-3-acetic acid (IAA). Auxins are involved in various plant processes, including phototropism and gravitropism.

Cytokinins

Chemical structure of Zeatin, a type of cytokinin.

Cytokinins are a group of hormones that promote cell division and differentiation. They are involved in processes such as shoot initiation and growth, leaf expansion, and delay of senescence. Zeatin is a well-known cytokinin found in many plants.

Gibberellins

File:Gibberellin A1.svg

Chemical structure of Gibberellin A1.

Gibberellins are a group of hormones that stimulate stem elongation, seed germination, and flowering. They are essential for breaking seed dormancy and promoting growth in various plant parts. Gibberellin A1 is one of the many gibberellins identified in plants.

Abscisic Acid

Chemical structure of Abscisic acid.

Abscisic acid (ABA) is a plant hormone that plays a crucial role in stress responses, such as drought tolerance, and in the regulation of stomatal closure. It is also involved in seed dormancy and abscission processes.

Ethylene

Chemical structure of Ethylene.

Ethylene is a gaseous plant hormone that influences fruit ripening, flower wilting, and leaf abscission. It is unique among plant hormones due to its gaseous state and is involved in the response to mechanical stress and pathogen attack.

Brassinosteroids

Chemical structure of Brassinolide, a type of brassinosteroid.

Brassinosteroids are a class of polyhydroxysteroids that promote cell expansion and elongation, vascular differentiation, and stress tolerance. Brassinolide is one of the most studied brassinosteroids.

Functions of Plant Hormones

Plant hormones regulate a wide range of physiological processes, including:

• Growth and Development: Hormones like auxins, cytokinins, and gibberellins are crucial for cell division, elongation, and differentiation.
• Stress Responses: Abscisic acid and ethylene play significant roles in plant responses to environmental stresses such as drought, salinity, and pathogen attack.
• Reproductive Development: Hormones regulate flowering, fruit development, and seed germination.
• Senescence and Abscission: Ethylene and abscisic acid are involved in leaf senescence and the abscission of leaves and fruits.

Related Pages

• Phototropism
• Gravitropism
• Seed dormancy
• Apical dominance