Plant Hormones Summary

  • Plant Hormones Overview

    • Plant hormones (also known as plant growth regulators) are chemical signals that coordinate growth, development, and responses to stimuli.
    • They are produced in varying concentrations and can dramatically affect physiological processes.
    • Hormones are mobile within the plant and can have multiple effects; several hormones may influence a single process.

  • Major Plant Hormones

    • Auxins: Promote growth (apical dominance), regulate stem elongation, and play a role in pattern formation, especially in roots.
    • Cytokinins: Stimulate cell division (cytokinesis), contribute to apical dominance alongside auxins, and promote lateral bud growth.
    • Gibberellins: Encourage rapid growth, flowering, and seed germination; involved in fruit growth and elongation.
    • Abscisic Acid (ABA): Slows growth, induces seed dormancy, and enhances drought tolerance by causing stomatal closure.
    • Ethylene: A gaseous hormone involved in fruit ripening, leaf abscission, and stress responses including flooding and wounding.

  • Auxins Practical Uses

    • Indolebutyric acid (IBA) stimulates root formation for plant cuttings.
    • Synthetic auxins (e.g., 2,4-D) can be herbicides targeting broadleaf weeds.

  • Cytokinins in Control of Growth

    • Primarily produced in actively growing tissues (roots, embryos).
    • Interaction with auxins and strigolactones influences apical dominance.

  • Functions of Gibberellins

    • Enhance stem elongation and seed germination post water intake.
    • For example, applied to grapes for increased fruit size.

  • Role of Abscisic Acid

    • Prevents germination until conditions are optimal, ensuring seeds only germinate when suitable (triggered by light, heavy rain, or cold).
    • Key for enhancing drought tolerance by closing stomata to conserve water.

  • Ethylene Production and Effects

    • Produced in response to stress, triggering ripening and apoptosis (cell death).
    • Regulates leaf abscission during autumn through a balance with auxins.

  • Summary Table of Major Plant Hormones
    | Hormone | Major Functions | Location of Production |
    |----------------|---------------------------------------------------------------------------------------------------|---------------------------------------------------|
    | Auxins (IAA) | Stimulates stem elongation, root formation, phototropism, and nutrient movement. | Apical meristems, young leaves, developing seeds.|
    | Cytokinins | Regulates cell division, nutrient movements, and promotes bud growth. | Roots, actively growing tissues. |
    | Gibberellins | Stimulates growth, flowering, and seed development. | Meristems of buds, roots, young leaves. |
    | Abscisic Acid | Inhibits growth, promotes seed dormancy and stomatal closure during drought. | Almost all plant cells. |
    | Ethylene | Promotes fruit ripening, leaf abscission, and responses to stress. | Most parts of the plant.