1. Chapter 5 BOT3015L Regulation of Plant Growth by Plant Hormones
Presentation created by Danielle Sherdan
All photos from Raven et al. Biology of Plants except when otherwise noted

2. Today The 5 main groups of plant hormones
Auxin
Cytokinins
Ethylene
Abscisic Acid
Gibberellins
Brassica rapa, a model plant species for experimentation
Design and begin group GA experiments
The 5 main groups of plant hormones
Auxin
Cytokinins
Ethylene
Abscisic Acid
Gibberellins
Brassica rapa, a model plant species for experimentation
Design and begin group GA experiments

3. Hormones Greek horman = to stimulate
Substance or chemical that is transported and causes specific physiological effects
Although a topic throughout biology, in this course, we will use plants as examples

4. Hormones in plants
Hormones can have effects on the cells that produce them and, after transport, at the target cells or tissues
Hormones can have inhibitory rather than stimulatory effects
5 main groups based on chemical structure

5. Auxin Production Shoot tips Developing seeds Some known actions
Establishment of polarity of root-shoot axis during embryogenesis
Cell elongation
Cell differentiation
Apical dominance
Lateral root formation and adventitious root formation
Fruit formation

6. Darwins’ (Charles and son) experiment
Under normal conditions, shoot tips bend towards the light
Without light on the tip, no bending
When not at tip, collar doesn’t prevent bending
Conclusion: Light is sensed at the tip, but response not at tip
New hypothesis: A substance or chemical is transported
Auxin later isolated from shoot tips and established to be involved in cell elongation
Drawings depicting seedlings of Zea (Gramineae family)

7. Evidence for the role of auxin in apical dominance
High auxin concentration
Low auxin concentration
Drawings depicting Coleus (Lamiaceae family)

8. Evidence for the role of auxin in adventitious root formation
With synthetic auxin
Without synthetic auxin
Adventitious roots growing from stem tissue
Saintpaulia (Gesneriaceae family)
Another example of misleading common name
The African violet is not in the violet family

9. Band of achenes removed
Evidence for the role of auxin in formation of fruit and structures of similar function (e.g. receptacle in strawberry)
Normal conditions
All achenes removed
Band of achenes removed
Without seed formation, fruits do not develop. Developing seeds are a source of auxin.
What do you expect?
Not shown: Auxin replacement restores normal fruit formation and can be used commercially to produce seedless fruits
However, too much auxin can kill the plant and thus synthetic auxins used commercially as herbicides
Fragaria (Rosaceae family)

10. Cytokinins Production Primarily root tips Some known actions
Cell division (cytokinesis)
Tissue culture
Delay leaf senescence

11. complexity of plant-hormone effects and interactions
Cytokinin and auxin
complexity of plant-hormone effects and interactions
Increasing auxin concentration
Increasing Cytokinin concentration
Auxin promotes root formation
Lack of differentiation when both are present
Cytokinin promotes shoot formation
Callus of Nicotiana (Solanaceae family)

12. Cytokinin delays leaf senescence (ageing and reabsorption of aged organs)
Transgenic
Untreated
Genetic modification to increase cytokinin biosynthesis
Nicotiana (Solanaceae family)

13. Ethylene
Production
In most tissues under stress, senescence, or ripening
Some known actions
Fruit ripening
Leaf and flower senescence
Leaf and fruit abscission (controlled separation of plant part from the main body)
Floral sex determination in monoecious species, promote female

14. Experimenting with plant response to ethylene commercial uses
Mutated ethylene receptor
Normal ethylene receptor levels
Both are 100 days after picking
Lycopersicon (Solanaceae family)

15. Experimenting with plant response to ethylene commercial uses
Mutated ethylene receptor
Normal ethylene receptor levels
8 days after pollination
Petunia (Solanaceae family)

16. Abscisic Acid (ABA) Production Mature leaves, especially under stress
Roots, then transported to shoots
Some known actions
Stress response
Stimulate stomatal closure
Inhibit premature germination of seeds
Embryogenesis
Seed dormancy maintenance

17. ABA induces stomatal closure a simplified diagram
Solutes (e.g. potassium and chloride ions) accumulate in guard cells causing water to accumulate in guard cells, making them turgid
ABA is one signal that causes guard cells to release solutes and thus release water, making them flaccid and closing the stoma (pore) between them
More about guard cells and experiments with guard cells coming up in a couple of weeks
Guard cell response to ABA is one topic of research in the Outlaw lab at FSU

18. Gibberellins Gibberellic acid (GA)
Production
In young, developing shoots and seeds
Some known actions
Cell division
Cell elongation
Stimulate seed germination
Stimulate flowering
Stimulate fruit development

19. Larger fruits that are easier to clean are attractive in markets
Commercial use of GA
Without GA
With GA
Larger fruits that are easier to clean are attractive in markets
Thompson seedless grapes (Vitis (Vitaceae family)

20. What are the effects of GA on the growth of Brassica rapa?
Why Brassica rapa?
Image from wikipedia.org

21. Today The 5 main groups of plant hormones Auxin Cytokinins Ethylene
Abscisic Acid
Gibberellins
Brassica rapa, a model plant species for experimentation
Design and begin group GA experiments

22. What are the effects of GA on the growth of Brassica rapa?
Why Brassica rapa?
1. Many economically valuable plants in the (Brassicaceae family)
Broccoli, cabbage, cauliflower, kale, radish, mustard, Canola oil
2. Members of the Brassicaceae family have become model plant species. Some characteristics that are important for model species include:
Relatively small genome
Easy to grow
Rapid life cycle
Broadly and thoroughly studied
Not atypical
Genetic tools available
See also Outlaw lecture notes and footnotes for more about Brassicas and model species

23. What are the effects of GA on the growth of Brassica rapa?
Production
In young, developing shoots and seeds
What do you expect?
What are your hypotheses?
Some known actions
Cell division
Cell elongation
Stimulate seed germination
Stimulate flowering
Stimulate fruit development

24. How would you design an experiment?
Question: What are the effects of GA on the growth of Brassica rapa?
Some of the materials available:
Seeds of normal (wild-type, WT) Brassica rapa
Seeds of Brassica rapa that produce less GA than normal (rosette, (ROS))
Materials for planting and growing plants in the greenhouse at Conradi
The following GA solutions:
0 M
3 M
30 M
For the other materials that your design requires, please discuss with TA

25. Aspects of good experimental design
Detailed step-by-step plan
How much?
How many?
What kind?
How long?
When?
Where?
Read about guidelines in lab manual
Control conditions in which the outcome is predictable
Repetition - general or exception

26. Data collection and presentation
The following must be on your group data sheet along with all of the group members’ names
“Official Group Datum Sheet for GA Experiment”
This datum record will remain by the experimental plants and all measurements will be recorded on this sheet and in individual’s lab notebook when the measurements are taken. These measurements will be provided to group members for the preparation of each’s individual GA report
Be sure to read the class policy, Academic Honor Policy, and lab manual (chpt 5) for information regarding group experiments and data collection
The experimental design, execution, and the report are worth 15% of your grade

27. Turn in… Then: To Conradi greenhouse with plants Experimental design
Datum sheet (include dates, space for signatures, space to record all observations and measurements, labels, official statement)
Schedule for experiment (who is doing what and when)
Contact info for each group member distributed to all group members
Then: To Conradi greenhouse with plants
Remember your independent experiment