Ch 39 Plant Responses - CHAPTER 39 PLANT RESPONSES TO...

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PLANT RESPONSES TO INTERNAL AND EXTERNAL SIGNALS CHAPTER 39
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Plants respond to a wide array of stimuli throughout its lifecycle Hormonal signals Gravity Direction of light Plant interactions between environmental stimuli and internal signals. Responses to Stimuli
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Animals and Plants differ in how they respond to stimuli Animals - mobility - behavioral Plants - environmental cues - Responses to Stimuli
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The ability to receive specific environmental and internal signals and respond to them in ways that enhance survival and reproductive success. Cellular receptors detect environmental changes - Hormonal changes - Injury repair - Seasonal changes Responses to Stimuli
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Plant growth patterns vary dramatically in the presence versus the absence of light. Potato grown in dark Potato grown in light Signal-transduction pathways link internal and environmental signals to cellular responses.
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Morphological adaptations in seedling growth The shoot does not need a thick stem. Leaves would be damaged as the shoot pushes upward. Don’t need an extensive root system No chlorophyll produced Energy allocated to stem growth
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The effect of sunlight on shoots ( greening ): The elongation rate of the stems slow. The leaves expand and the roots start to elongate. The entire shoot begins to produce chlorophyll. (a) Before exposure to light (b) After a week’s exposure to natural daylight
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Signal transduced pathways: greening response. Three stages: 1. Reception 2. Signal transduction 3. Response
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Reception for Greening: The receptor is called a phytochrome : a light- absorbing pigment attached to a specific protein. Located in the cytoplasm. Sensitive to very weak environmental and chemical signals Signal is then amplified by a second messenger
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Transduction: Second messenger produced by the interaction between phytochrome and G- protein G-protein activates enzyme with produces Cyclic GMP (2 nd messenger) Ca 2+ -calmodulin is also a 2 nd messenger
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Response Cyclic GMP and Ca 2+ -calmodulin pathways lead to gene expression for protein that activates greening response Response ends when “switch-off” is activated (protein phosphatases)
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Signal Transduction in Plants: Greening
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Hormones- are chemical signals that travel to target organs Only small amts are needed Often the response of a plant is governed by the interaction of two or more hormones. Phototropism and Negative phototropism Hormone
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Early Experiments of Phototropism
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Went Experiment (1926) of Phototropism auxin
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Some major classes of plant hormones: Auxin- phototropism Cytokinins- root growth Gibberellins- growth Abscisic acid- inhibits growth Ethylene- promote fruit ripening Brassinosteroids- inhibits root growth Many function in plant defense against pathogens
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Polar Auxin Transport: A Chemiosmotic Model Fig. 39-8 Cross-linking
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This note was uploaded on 04/20/2011 for the course BIOL 172 taught by Professor Huddleston,m during the Spring '08 term at University of Hawaii, Manoa.

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Ch 39 Plant Responses - CHAPTER 39 PLANT RESPONSES TO...

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