Chapter 39 - CR97-03

Chapter 39 - CR97-03 - Chapter 39 Plant Responses to...

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Chapter 39 Chapter 39 Plant Responses to Internal and External Signals 1 of 29 of 29
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39.1: Signal transduction pathways link 39.1: Signal transduction pathways link signal reception to response signal reception to response Plants must respond to any environmental change that comes their way since they’re rooted to the ground Cellular receptors Used by the plant to detect important changes in their environment Certain cells must have an appropriate receptor for a stimulus to elicit a response A potato left growing in darkness will produce shoots that do not appear healthy (pale with unexpanded leaves), and will lack elongated roots These are morphological adaptations for growing in darkness collectively referred to as etiolation 2 of 29 of 29
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After the potato is exposed to light the plant undergoes profound changes called de-etiolation , in which shoots and roots grow normally The potato’s response to light is an example of cell-signal processing CELL WALL CYTOPLASM 1 Reception 2 Transduction 3 Response Receptor Relay molecules Activation of cellular responses Hormone or environmental stimulus Plasma membrane Figure 39.3 3 of 29 of 29
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Reception Internal and external signals are detected by receptors Proteins undergo conformational changes in response to specific stimuli Transduction Second messengers transfer and amplify signals from receptors to proteins that cause specific responses Response Ultimately, a signal transduction pathway leads to a regulation of one or more cellular activities In most cases, responses to stimulation involve the increased activity of certain enzymes 4 of 29 of 29
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An example of signal transduction in plants 1 The light signal is detected by the phytochrome receptor, which then activates at least two signal transduction pathways. 1 Reception 2 Transduction 3 Response CYTOPLASM Plasma membrane Phytochrome activated by light Cell wall Light cGMP Second messenger produced Specific protein kinase 1 activated Transcription factor 1 NUCLEUS P P Transcription Translation De-etiolation (greening) response proteins Ca 2+ Ca 2+ channel opened Specific protein kinase 2 activated Transcription factor 2 2 One pathway uses cGMP as a second messenger that activates a specific protein kinase.The other pathway involves an increase in cytoplasmic Ca 2+ that activates another specific protein kinase. 3 Both pathways lead to expression of genes for proteins that function in the de-etiolation (greening) response. Figure 39.4 5 of 29 of 29
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Transcriptional Regulation Transcription factors bind directly to specific regions of DNA and control the transcription of specific genes One such factor is dependent upon cGMP Another such factor is depended upon Ca 2+ Post-Translational Modification of Proteins Involves activating existing proteins Kinases and Phosphatases De-Etioloation (“Greening”) Proteins Certain signal response enzymes are involved in
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This note was uploaded on 04/07/2008 for the course BIO 103 taught by Professor Mannino during the Fall '08 term at Long Island U..

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Chapter 39 - CR97-03 - Chapter 39 Plant Responses to...

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