1. Plant Growth Regulators
Chemical Messengers

2. They provide for plant growth and development
Hormones
Hormones are “chemical messengers” directing plant development & survival.
They provide for plant growth and development

3. Other methods of regulation are accomplished by
Chemical reactions to stimuli
Sunlight on shoots
Water on roots
Insects (chewing) on leaves
Stimulate signal transduction pathways

4. Hormones = Growth Regulators
6 main plant hormones
1. Auxins
2. Gibberellins
3. Cytokinins
4. Ethylene
5. Brassinosteroids
6. Abscisic acid

5. A good example of hormones at work: Etiolation
Plant growth in the absence of sunlight
Environmental “awareness”
Accomplished by hormones.

6. Auxins Stimulate cell growth thru cell elongation
Produced in apical & lateral buds & meristems
Auxins move mainly from apex (top) down.
Auxins

7. Remember zones of elongation?

9. To demonstrate:
Cells elongate under the auxin

10. Auxins Greatest concentration in terminal bud.
Ensure apical dominance. Lateral bud growth is inhibited by other hormones

11. In addition…(auxin’s roles)
Flower development
Root growth (Rootone) –

12. Indoleactic acid (IAA)(natural).
examples of Auxin
Indoleactic acid (IAA)(natural).
2,4-dichlorophenoxy acetic acid (2-4D)(synthetic)

13. Next: Gibberellins (Gibberellic Acid GA)
Stimulates cell division in stem, root, & leaf growth

14. Gibberellic acid
LOOK! Functional groups!

15. Brassinosteroids are also growth regulators
(no need to know)
Brassinosteroids are also growth regulators
Cell elongation ( sound familiar?)
Vascular differentiation
Stress tolerance

16. Cytokinins regulate growth
Produced in roots
Transported throughout plant.
Affect cell division, apical dominance

17. Cytokinins Esp. in root meristems
Interact with auxins, stimulate bud formation.

18. Cytokinins
inhibits leaf senescence (seasonal leaf drop).

19. Ethylene gas Diffuses easily throughout a plant
Facilitates ripening of fruits, apoptosis (?) leading to loss of leaves & flowers.

20. Ethylene (gas) “the aging hormone”
In fruits & leaves, breaks down chlorophyll and lets colors show through.

21. Plant growth Inhibitor
Abscisic Acid (ABA)
Widespread in plants. moves freely through plant
ABA made by the leaves.
Interacts with other hormones in the plant; counteracts the growth effects of auxins & gibberellins.

22. Abscisic Acid Predominant during plant dormancy
Produced when plants are under stress

23. Abscisic Acid
Maintains seed dormancy Responsible for seed germination occurring only under favorable conditions

24. Additional ways plants respond to changes in their environment: It ain’t all hormones!
The role of photoreceptors and signal transduction pathways

25. PHYTOCHROMES: 1 isomer stops growth, the other (far red) starts it.

26. Photoperiodism
Short day plants
Long day plants

27. Experiments have confirmed that it is actually the length of darkness, not light, that affects flowering Greenhouses apply this science to get flowers to be ready for certain seasons

28. Other environmental stimuli
(phototropism)
Gravitropism
Thigmotropism
Temperature stresses
Responses to insect infestations
Plants produce R gene products