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

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. Hormonal Action
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

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
/ \

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: Gravitropism:
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: Root: 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