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Plant Hormones

Plant Hormones. Signal Transduction Pathways. Reception—Receipt of a hormonal or environmental stimulus by a receptor—a protein that undergoes a conformational change in response to the stimulus Transduction—The transfer and amplification of the signal from the receptor

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Plant Hormones

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  1. Plant Hormones

  2. Signal Transduction Pathways • Reception—Receipt of a hormonal or environmental stimulus by a receptor—a protein that undergoes a conformational change in response to the stimulus • Transduction—The transfer and amplification of the signal from the receptor • Response—Regulation of one or more cell activities

  3. Signal Transduction Pathway

  4. Types of Responses • Transcriptional Regulation—Bind to regions of DNA & control transcription of certain genes • Activate positive transcriptional factors • Deactive negative transcriptional factors • Post Translational Modification of Proteins Activation of proteins usually by phosphorylation

  5. Plant Responses • Tropism—Plant growth toward or away from a stimulus • Phototropism—Growth toward light

  6. Early Experiments

  7. Plant Hormones—AUXIN • Promotes elongation of coleoptiles (stems) • Moves from the apical meristem down the stem and causes the stem to elongate • Involved in lateral branching of roots (rooting powder) • Also affect secondary growth in vascular cambium and promotes growth of fruit when released by the seed

  8. Plant Hormones—CYTOKININS • Stimulate cytokinesis; produced by roots • Produced in actively growing roots, embryos, and fruits • Act along with auxin • Ratio of auxin to cytokinins control apical dominance—more auxin more apical growth; more cytokinins—more lateral growth

  9. Plant Hormones—GIBBERELLINS • Promote stem elongation and leaf growth • Produced by roots and young leaves • Results in rapid growth of floral stalk when environment favors reproduction • Along with auxin causes fruit to set • Embryo of seeds is rich in gibberellins, this hormone signals seeds to break dormancy and germinate

  10. Plant Hormones—ABSCISIC ACID • Antagonizes the action of the growth hormones • High levels of ABA inhibit seed germination • ABA:gibberellins ratio determines whether seed will remain dormant or germinate • Enables plants to withstand drought by controlling uptake of K+ by guard cells

  11. Plant Hormones—ETHYLENE • Produced in response to drought, flooding, mechanical pressure, injury, and infection. • Also occurs during fruit ripening and apoptosis (programmed cell death) • Responsible for leaf abscission (aging leaves produce less auxin making them sensitive to ethylene) • Cause starch in fruit to break down to sugar

  12. Plant Hormones--BRASSINOSTEROIDS • Similar to cholesterol • Induce cell elongation • Inhibits root growth • Retard leaf abscission • Promote xylem differentiation

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