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4.4.8: Chapter Summary

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    Plant hormones—naturally occurring compounds synthesized in small amounts—can act both in the cells that produce them and in distant tissues and organs. Auxins are responsible for apical dominance, root growth, directional growth toward light, and many other growth responses. Cytokinins stimulate cell division and counter apical dominance in shoots. Gibberellins inhibit dormancy of seeds and promote stem growth. Abscisic acid induces dormancy in seeds and buds, and protects plants from excessive water loss by promoting stomatal closure. Ethylene gas speeds up fruit ripening and dropping of leaves. Other signaling molecules, such as salicylic acid and jasmonates are important to plant defense.

    After completing this chapter, you should be able to...
    • Explain the defining characteristics of a hormone.
    • Name the five major plant hormones and identify their locations of synthesis, transport, and actions.
    • Describe interactions among the five major plant hormones.
    • Explain the mechanism of polar auxin transport.
    • Define apical dominance and explain the role of auxin in maintaining it.
    • Interpret and predict the outcome of an experiments demonstrating the actions of auxin and gibberellic acid.
    • Describe the commercial applications of auxin, ethylene, and gibberellins.
    • Identify several signaling molecules beyond the five major plant hormones and describe their effects.
    • Distinguish between the hypersensitive response and systemic acquired response.
    • Explain the mechanisms by which signaling compounds aid in plant defense against pathogens and herbivores.


    Curated and authored by Melissa Ha from 30.6 Plant Sensory Systems and Responses from Biology 2e by OpenStax (licensed CC-BY). Access for free at

    This page titled 4.4.8: Chapter Summary is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .

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