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Chapter 5BOT3015L
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
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•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
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
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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
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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
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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
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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)
Darwins’ (Charles and son) experiment
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High auxin concentration
Low auxin concentration
Drawings depicting Coleus (Lamiaceae family)
Evidence for the role of auxin in apical dominance
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Evidence for the role of auxin in adventitious root formation
With synthetic auxin Without synthetic auxin
Saintpaulia (Gesneriaceae family)Another example of misleading common name
The African violet is not in the violet family
Adventitious roots growing from stem tissue
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Evidence for the role of auxin in formation of fruit and structures of similar function
(e.g. receptacle in strawberry)
Fragaria (Rosaceae family)
Band of achenes removed
What do you expect?
Not shown: Auxin replacement restores normal fruit formation and can be used commercially to produce seedless fruits
All achenes removed
Normal conditions
Without seed formation, fruits do not develop. Developing seeds are a source of auxin.
However, too much auxin can kill the plant and thus synthetic auxins used commercially as herbicides
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Cytokinins
Production• Primarily root tips
Some known actions
• Cell division (cytokinesis)
• Tissue culture
• Delay leaf senescence
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Increasing auxin concentration
Increasing Cytokinin concentration
Auxin promotes root formation
Cytokinin promotes shoot formation
Lack of differentiation when both are present
Cytokinin and auxin complexity of plant-hormone effects and interactions
Callus of Nicotiana (Solanaceae family)
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Cytokinin delays leaf senescence (ageing and reabsorption of aged organs)
Transgenic Untreated
Genetic modification to increase cytokinin biosynthesis
Nicotiana (Solanaceae family)
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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
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Experimenting with plant response to ethylenecommercial uses
Mutated ethylene receptor
Normal ethylene receptor levels
Both are 100 days after picking
Lycopersicon (Solanaceae family)
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Experimenting with plant response to ethylenecommercial uses
Mutated ethylene receptor
Normal ethylene receptor levels
8 days after pollination
Petunia (Solanaceae family)
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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
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ABA induces stomatal closurea 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
Guard cell response to ABA is one topic of research in the Outlaw lab at FSU
More about guard cells and experiments with guard cells coming up in a couple of weeks
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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
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Commercial use of GA
Thompson seedless grapes (Vitis (Vitaceae family)
Without GA With GA
Larger fruits that are easier to clean are attractive in markets
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What are the effects of GA on the growth of Brassica rapa?
Why Brassica rapa?
Image from wikipedia.org
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•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
Today
![Page 22: Chapter 5 BOT3015L Regulation of Plant Growth by Plant Hormones](https://reader035.vdocument.in/reader035/viewer/2022062304/56812a45550346895d8d78b3/html5/thumbnails/22.jpg)
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
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What are the effects of GA on the growth of Brassica rapa?
Production• In young, developing shoots and seeds
Some known actions
• Cell division
• Cell elongation
• Stimulate seed germination
• Stimulate flowering
• Stimulate fruit development
What do you expect?What are your hypotheses?
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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
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Aspects of good experimental design
Detailed step-by-step planHow much? How many? What kind? How long?When? Where?Read about guidelines in lab manual
Repetition - general or exception
Control conditions in which the outcome is predictable
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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
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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
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