L21 Environmental Influences

L21 Environmental Influences - ReviewofLecture20

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Review of Lecture 20 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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Light Perception One major type of response to light in plants is  phototropism (from the Greek tropos,“turn”),  growth toward or away from light 1. Growth toward light is known as  positive   phototropism (shoots) 2. Growth away from light is known as  negative   phototropism (roots)
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No light Growth Response Light does not cause auxin degradation but  rather changes its distribution 1. In shoots this promotes growth on the  side with higher auxin concentrations  2. In roots high auxin concentrations  inhibit growth and therefore the dark  side of the root grows less Auxin concentration
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Light Responses Other Blue-light responses  are  regulated by the  phototropins. There is  genetic redundancy (more  than 1 gene) reflecting  functional overlap. Phototropism  Chloroplast  migration Stomatal  opening
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Phytochrome P R P FR Red light Far-red light Dark Reversion Synthesis from  precursors Biological Response Breakdown
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Flowering Time 1. The nature of the cellular component that measures night  length is not  known 2. Phytochrome itself does not  serve this function 3. By the end of the night P FR  has decayed back to P R 4. It is thought that a subpopulation of phytochrome  molecules may be involved in measuring night length
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Transmitting the Message 1. FT protein is synthesized in  leaves and transmitted to the  SAM 2. In the SAM, FT protein acts  together with a transcription  factor, FD, to initiate floral  development mRNA SAM FT mRNA FD FT Protein
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Circadian Rhythms From Raven, Evert and Eichhorn, Biology of Plants, 6th edition
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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 21 Outline Sensing the Environment: Chapter 11 1. Gravitropism 2. Thigmotropism 3. Defense Responses 4. Volatiles a) Sending out signals (love and death) b) Tritrophic Interactions c) Controlling the weather
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Gravitropism Growth toward (+) or away from (-) gravity 1. Shoots grow away from gravity and show  negative gravitropism 2. Roots grow toward gravity and therefore show  positive gravitropism
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gravity From Raven, Evert and Eichhorn, Biology of Plants, sixth edition Negative Gravitropism
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How do plants sense gravity? Three current hypotheses attempt to explain how  plants sense and respond to gravity 1. Starch-statolith hypothesis 2. Protoplast pressure hypothesis (gravitational  pressure hypothesis) 3. Tensegrity model (“tensional integrity”) 
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1. Starch-statolith  hypothesis This hypothesis proposes 
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L21 Environmental Influences - ReviewofLecture20

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