2. Regulating Growth and Development: The Plant Hormones Chapter 27

3. Hormones Hormone- gr. to excite. Organic substances produced in small amounts that regulate and coordinate metabolism, growth, and morphogenesis.

5. Six Major Classes of Plant Hormones Auxins –Leaf primordia, young leaves, developing seeds. –Polarly (unidirectionally) and nonpolarly. Cytokinins –Root tips. –From roots to shoots via xylem. Ethylene –Most tissues in response to stress. –Diffusion from site of synthesis. Abscisic acid –Mature leaves and roots, seeds. –From leaves in phloem and from the roots in the xylem. Gibberellins –Young tissues of the shoot and developing seeds. –Xylem and phloem. Brassinosteroids –Young tissues and throughout the plant. –They act locally.

6. Auxin is the only plant hormone known to be transported polarly. Polar transport is basipetal (toward the base).

7. Auxin Provides Chemical Signals That Communicate Information Over Long Distances Apical Dominance- inhibitory influence of the apical bud upon lateral buds.

8. Auxin Plays a Role in the Differentiation and Regeneration of Vascular Tissue

9. Auxin Promotes Fruit Development

10. Auxin Promotes the Formation of Lateral and Adventitious Roots

11. Auxin Prevents Abscission

12. Synthetic Auxins Kill Weeds- Herbicides

13. Ethylene Plays a Role in Fruit Ripening

14. Ethylene May Inhibit or Promote Cell Expansion = inhibit

15. Cytokinins Promote Cell Division

16. Cytokinins Delay Leaf Senescence

17. Cytokinins Promote the Growth of Lateral Buds

18. Abscisic Acid (ABA) Prevents Seed Germination

19. Abscisic Acid Plays a Role as a Root-to-Shoot Signal

20. Abscisic Acid is Responsible for Stomatal Closure

21. Gibberellin (GA) causes dwarf mutants to grow tall. Gibberellin causes hyperelongation of shoots by stimulating cell division and elongation.

22. Gibberellin Plays Multiple Roles in 1) Breaking seed dormancy 2) In germination

23. Gibberellin Can Cause Bolting

24. Gibberellin Affects Fruit Development

25. Brassinosteroids

26. Additional Chemical Signals Salicylic acid- signal in defense responses to plant pathogens. Jasmonates- plant growth regulation and defense. Polyamines- growth and development; mitosis and meiosis. Systemin- long-distance signal that activates chemical defenses against herbivores. Nitric Oxide- signal in hormonal and defense responses.

27. External Factors and Plant Growth- Chapter 28

28. Tropism- directional growth in response to an external stimulus.

29. Phototropism- the curving of a growing shoot toward light. –Auxin? Frits Went

31. Phytochrome and Photoperiodism

32. Gravitropism- the response of shoot or root to gravity. –1st Cytokinin –2nd Auxin

35. Thigmotropism- the response to contact with a solid object.

36. Heliotropism- the orientation of leaves and flowers to the sun. –Turgor pressure changes of the pulvinus.

37. Pulvinus- jointlike thickening at the base of the petiole or petiolule.

38. Growth response unrelated to the direction of the external stimulus Nastic Movement- gr. nastos= closed- pressed. –Nyctinasty –Thigmonasty Thigmomorphogenesis

39. Nyctinasty- the up and down movement of leaves in response to daily rhythms (night and day).

40. Thigmonasty- nastic movements resulting from touch.

42. Thigmomorphogenesis- the alteration of plant growth patterns in response to mechanical stimuli.