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Figure 39.0 A grass seedling growing toward a candle’s light

Chapter 39: Plant Hormones. Figure 39.0 A grass seedling growing toward a candle’s light. Review for test Test tomorrow all multiple choice. Hormones. Chemical signals Produced in one part of plant and effect other parts Trigger responses in target cells and tissues

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Figure 39.0 A grass seedling growing toward a candle’s light

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  1. Chapter 39: Plant Hormones Figure 39.0 A grass seedling growing toward a candle’s light

  2. Review for test • Test tomorrow all multiple choice

  3. Hormones • Chemical signals • Produced in one part of plant and effect other parts • Trigger responses in target cells and tissues • Small amounts produce substantial changes

  4. General plant hormones • Auxins • Gibberellins • Cytokinins • Abscisic acid • Ethylene

  5. Table 39.1 An Overview of Plant Hormones Study This!!

  6. Hormone (red) binds to receptor (receptor) which activate a 2nd messenger (blue). This triggers 1.Proton pumps 2.Production of golgi vesicles 3.Transcription and translation Hormonal Action

  7. H+

  8. Figure 39.7 Cell elongation in response to auxin: the acid growth hypothesis

  9. Acid Growth Hypothesis • 1. Auxin, produced by apical mersitems in buds, trigger H+ pumps • 2. H+ pumps move ions into cell wall matrix • 3. Acidity in wall increases and breaks bonds in the cellulose fibers • 4. Cell wall weakens and water enters • 5. Cell elongates

  10. Auxin & Cytokinins

  11. Auxin: Control of Apical Dominance Effect on Stems: • Auxin produced by terminal bud inhibits growth of axillary buds. Plant grows taller • Cytokinins produced by roots stimulate axillary bud growth • Lower buds grow faster than those close to terminal • If terminal bud is cut, (i.e. auxin is removed) and axillary buds grow and plant gets fuller

  12. Auxin: Control of Apical Dominance Effect on Roots: • Auxin stimulates root branching • High concentrations of auxin INHIBIT root growth • Cytokinins inhibit root branching

  13. Apical Dominance

  14. Function of cytokinins • Promotes cell division. • Morphogenesis. • Lateral bud development. • Delay of senescence. • Made in root, travel in xylem

  15. Gibberellin

  16. Discovered in association with Foolish disease of rice (Gibberella fujikuroi) uninfected infected

  17. Effects of Gibberellins • Make in roots and young leaves • General cell elongation in leaves and stems (not roots). • Found in embryo of seeds and leads to the breaking of dormancy. • Promotion of flowering. • Commercially used for spraying on Thompson’s seedless grapes

  18. Figure 39.11 The effect of gibberellin treatment on seedless grapes

  19. Abscisic acid

  20. Functions of abscisic acid • General growth inhibitor. • Prevents seeds from germinating (if ABA is removed from seeds, germinations begins!) • Causes closing of stomata • “Winterization”effect on plants • Produced in response to stress.

  21. Ethylene H H \ / C = C / \ H H

  22. Functions of ethylene • Gaseous • Causes fruit to ripening. • Senescence and abscission. • Interference with auxin transport. • Initiation of stem elongation and bud development.

  23. Tropism

  24. Tropisms • Phototropism: • shoots or stems bends towards light enhancing photosynthesis • Gravitropism: • Plants uses statoliths to tell which way is “up” or “down” • Roots display positive gravitropism (grows down towards the earth) and the shoot displays negative gravitropism (grows up out of the earth)

  25. Growth movement

  26. Phototropism • Light straight above plants • Auxin amounts equal on both sides • Cell elongation equal on both sides • Stems grow straight up!

  27. Phototropism • Light at an angle • Auxin accumulates (moves) to the shaded side

  28. Phototropism • High auxin concentration promotes cell growth on shaded side • Stem grows towards light source • Positive phototropism

  29. Gravitropism • Shoot: • Grows away from pull of gravity • Negative gravitropism • Root: • Grows toward pull of gravity • Positive gravitropism

  30. If plant falls over… • In roots: • Statoliths (starch grains) settle to the bottom of the cells • Triggers the movement of Ca2+ • Causes lateral movement of auxin

  31. Roots and stems respond……the effects of auxin on roots and shoots are opposing!!!! • IN ROOTS: • 1. Low auxin, cells elongate • 2. High auxin, inhibitory response, no elongation • Roots curve down • IN SHOOTS • 3. Low auxin inhibits elongation • 4. High auxin, stimulates cell elongation • Shoots curve up

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