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Outline

Outline. Plant Responses Tropisms Nastic Movements Plant Hormones Auxins Gibberellins Cytokinins Abscisic Acid Ethylene Photoperiodism. Plant Responses. Tropisms Plant growth toward or away from a unidirectional stimulus is called a tropism Positive is towards stimulus

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Outline

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  1. Control of Growth and Responses in Plants

  2. Outline • Plant Responses • Tropisms • Nastic Movements • Plant Hormones • Auxins • Gibberellins • Cytokinins • Abscisic Acid • Ethylene • Photoperiodism

  3. Plant Responses • Tropisms • Plant growth toward or away from a unidirectional stimulus is called a tropism • Positive is towards stimulus • Negative is away from stimulus • Phototropism - Light • Gravitropism - Gravity • Thigmotropism - Touch

  4. Phototropism

  5. Phototropism • Positive phototropism: • Occurs because cells on the shady side of the stem elongate • A pigment related to riboflavin thought to act as a photoreceptor when phototropism occurs • Auxin migrates to shady side of stem • Shady sides elongate faster than bright side

  6. Gravitropism • When a plant is placed on its side, the stem grows upward, opposite of the pull of gravity • Stems with root caps grow downward • Root cells contain statoliths • Auxin is responsible for: • Positive gravitropism of roots, and • Negative gravitropism of shoots

  7. Gravitropism

  8. Thigmotropism • Unusual growth due to contact with solid objects is called thigmotropism • Coiling of tendrils • Thigmomorphogenesis occurs when the entire plant responds to the presence of environmental stimuli • Wind • Rain

  9. Coiling Response

  10. Nastic Movements • Nastic movements: • Do not involve growth and • Are not dependent on the stimulus direction • Seismonastic movements result from: • Touch • Shaking, or • Thermal stimulation • Sleep movements: • Occur daily in response to light and dark changes • Prayer Plant

  11. Seismonastic Movement

  12. Sleep Movement

  13. Circadian Rhythms • A circadian rhythms: • Biological rhythms with a 24-hour cycle • Tend to be persistent • Rhythm is maintained in the absence of environmental stimuli • Caused by a biological clock

  14. Plant Hormones • Almost all communication on a plant is done by hormones • Synthesized in one part of the plant • Travels within phloem in response to the appropriate stimulus

  15. Auxins • Auxin is produced in shoot and apical meristem and is found in young leaves and in flowers and fruits • Apically produced auxin prevents the growth of axillary buds • Apical dominance • Weak solution of auxin applied to woody cutting causes rapid growth of adventitious roots • Promotes fruit growth

  16. Apical Dominance

  17. Demonstrating Phototropism

  18. How Auxins Work • Auxins bind to plasma membrane receptors • Activated proton pumps H+ out of cell • Cell wall loosens • Turgor pressure increases due to the entry of water • Cell enlarges

  19. Auxin Mode of Action

  20. Gibberellins • Gibberellins: • Growth promoting hormones • Bring about elongation of the resulting cells • Gibberellic acid • Stem elongation • Breaking of dormancy

  21. Effect of Gibberellins

  22. Gibberellic Acid:Structure and Mode of Action

  23. Cytokinins • Cytokinins • A class of plant hormones that promote cell division • Derivatives of adenine • Prevent senescence • Initiate growth

  24. Interaction of Hormones

  25. Abscisic Acid • Abscisic acid (ABA): • Initiates and maintains seed and bud dormancy, and • Brings about closure of stomata • Produced by: • Any “green tissue” with chloroplasts • Monocot endosperm, and • Roots

  26. Abscisic Acid:Control of Stoma Opening

  27. Ethylene • Ethylene is involved in abscission • Once abscission has begun: • Ethylene stimulates certain enzymes • Cause leaf, fruit, or flower to drop • Also ripens fruit by increasing activity of enzymes that soften fruit

  28. Functions of Ethylene

  29. Photoperiodism • Photoperiodism: • Any physiological response prompted by changes in day or night length • Short-day plants • Long-day plants • Day-neutral plants • Some plants may require a specific sequence of day lengths in order to flower

  30. Photoperiodism and Flowering

  31. Phytochrome • Phytochrome is a blue-green leaf pigment that alternately exists in two forms • Phytochrome red (Pr) • Phytochrome far-red (Pfr) • Conversion of forms allows a plant to detect photoperiod changes • Also promotes seed germination and inhibits stem elongation

  32. Phytochrome Conversion Cycle

  33. Phytochrome Control of Growth Pattern

  34. Review • Plant Responses • Tropisms • Nastic Movements • Plant Hormones • Auxins • Gibberellins • Cytokinins • Abscisic Acid • Ethylene • Photoperiodism

  35. Control of Growth and Responses in Plants

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