Chapter 5 BOT3015L Regulation of Plant Growth by Plant Hormones

1. Chapter 5BOT3015LRegulation 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. When not at tip, collar doesn’t prevent bending Under normal conditions, shoot tips bend towards the light Without light on the tip, no bending Darwins’ (Charles and son) experiment 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. High auxin concentration Low auxin concentration Evidence for the role of auxin in apical dominance 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. Normal conditions All achenes removed Evidence for the role of auxin in formation of fruit and structures of similar function (e.g. receptacle in strawberry) 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. Cytokinin and auxin complexity of plant-hormone effects and interactions Auxin promotes root formation Lack of differentiation when both are present Cytokinin promotes shoot formation Increasing auxin concentration Increasing Cytokinin concentration 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 ethylenecommercial uses Mutated ethylene receptor Normal ethylene receptor levels Both are 100 days after picking Lycopersicon (Solanaceae family)

15. Experimenting with plant response to ethylenecommercial 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 is one signal that causes guard cells to release solutes and thus release water, making them flaccid and closing the stoma (pore) between them Solutes (e.g. potassium and chloride ions) accumulate in guard cells causing water to accumulate in guard cells, making them turgid ABA induces stomatal closurea simplified diagram 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. GibberellinsGibberellic 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. 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… • 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