L20 Light Regulated Responses

L20 Light Regulated Responses - ReviewofLecture19

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Review of Lecture 19 Plant Growth Regulators II: Chapter 11 1. Cytokinins 2. Plant tissue culture 3. Gibberellins 4. Abscisic Acid 5. Ethylene 6. Brassinosteroids 7. Other Regulators
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Tobacco tissue culture From Raven, Evert and Eicchorn, Biology of Plants, sixth edition
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Gibberellins 1. GAs are synthesized in apical meristems, young leaves and  embryos (like auxins) 2. Gibberellins are one of several types of hormones that  promote stem elongation 3. Exogenous application of GAs can reverse dwarfism 4. GAs play a role in both embryo growth and seed  germination 5. GAs play a role in flowering in some plants 6.  GAs contribute to fruit formation
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Abscisic Acid 1. It is now known that ABA plays no  direct role in  abscission 2. ABA plays a major role in seed development 3. ABA stimulates the production of seed storage proteins 4. ABA plays an important role in seed dormancy 5. Mutants that lack ABA or are insensitive to ABA fail to  become dormant (for example, viviparous mutants of  maize)
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GA and ABA GA and ABA have antagonistic effects in several  important processes 1. Seed germination 2. Floral transition 3. Fruit development GA promotes these processes while ABA inhibits  them
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Ethylene The triple response 1. Stem elongation slows 2. Stem thickens 3. Stem grows horizontally Chap.11, pg.243
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Ethylene and Abscission 1. Ethylene promotes shedding (abscission) of leaves, flowers  and fruits in a variety of species 2. Ethylene triggers the enzymes that cause cell wall  dissolution 3. In many systems, however, abscission is controlled by an  interaction between auxin and ethylene 4. Auxin seems to decrease the sensitivity of abscission zone  cells to ethylene
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Plant Hormones: Brassinosteriods 1. Newly discovered group of hormones that act like auxin 2. They were first discovered in the genus Brassica and hence were  named brassinosteroids 3. These compounds bind to plasma membrane receptor proteins but do  not enter the cell 4. Brassinosteriods stimulate cell division and elongation in stems,  cause xylem differentiation, promote pollen tube growth, slow root  growth, enhance ethylene synthesis and delay senescence 5. Mutants defective in brassinosteriod pathways look like auxin  mutants
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The challenges 1. Harvesting light energy 2. Staying wet when things get dry 3. Dealing with gravity 4. Divide or be conquered  5. Leveraging resources
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Lecture 20 Outline Sensing the environment: Chapter 11 1. Phototropism 2. Photomorphogenesis 3. Light Receptors 4. Photoperiods 5. Induction of flowering 6. Circadian Rhythms
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Plant Tropisms Tropism : a growth response involving bending, or  curving, of a plant toward or away from an external  stimulus that determines the direction of movement
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L20 Light Regulated Responses - ReviewofLecture19

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