Phytohormones | Biology for JAMB PDF Download

Introduction

Phytohormones, also known as plant hormones or plant growth regulators, are chemical substances that regulate various physiological processes in plants. These hormones play a crucial role in plant growth, development, and responses to environmental stimuli. They are produced naturally within plants and are responsible for coordinating growth, flowering, fruit development, and many other important plant functions.

Examples of Phytohormones

Auxins

Auxins are a group of phytohormones that regulate plant growth and development. The most abundant auxin in plants is indole-3-acetic acid (IAA). Auxins are primarily produced in the apical meristems of the plant and then transported to different parts, where they control cell elongation, root formation, and fruit development.

Function of Auxins:

• Promote cell elongation: Auxins stimulate cell elongation, which is crucial for plant growth. They regulate the elongation of cells in the stem, promoting upward growth towards light.
• Root formation: Auxins play a vital role in the development of roots. They inhibit lateral root growth and promote the formation of new roots from stem cuttings.
• Apical dominance: Auxins suppress the growth of lateral buds, maintaining the dominance of the apical bud. This ensures that the plant grows upward and not sideways.
• Fruit development: Auxins are involved in fruit growth and development. They promote the development of fruits by stimulating cell division and enlargement.

Gibberellins

Gibberellins are another group of phytohormones that regulate plant growth and development. These hormones are involved in processes such as seed germination, stem elongation, flowering, and fruit development.

Function of Gibberellins:

• Seed germination: Gibberellins break seed dormancy and promote seed germination. They stimulate the synthesis of enzymes that degrade stored nutrients in the seed, providing energy for seedling growth.
• Stem elongation: Gibberellins promote stem elongation by stimulating cell division and elongation. They are responsible for the rapid growth of stems, especially in the absence of light.
• Flowering: Gibberellins play a role in flowering. They promote the development of floral buds and are involved in the regulation of flowering time.
• Fruit development: Gibberellins influence fruit development by stimulating cell division and enlargement. They can also delay fruit ripening in some plants.

These are just two examples of phytohormones and their functions. Other important phytohormones include cytokinins, abscisic acid (ABA), and ethylene. Together, these hormones orchestrate plant growth, development, and responses to environmental cues, ensuring the survival and success of plants in various conditions.