CH39_summary - Plant Responses to Internal and External...

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Plant Responses to Internal and External Stimulation Chapter 39 Signal Reception to Response • Three Steps Reception • Signals are detected • Proteins change shape in response to specific stimuli Transduction • Second messengers transfer and amplify signals from receptors to proteins that cause a specific response Response • Typically involves activation of enzymes by stimulating transcription of mRNA for the enzyme ( Transcriptional Regulation ) • Also, may activate existing enzyme molecules • Called post-translational modification of proteins Stimuli • Stimuli could be • Internal signals • Specific hormones • External signals • Light • Tactile (touch) • Heat • Etc. • Stimulus Example: Light • The absence of light stimulates a process or growth condition called “etiololation” • Etiolation is a collection of morphological adaptations for growing in darkness • Good for growing underground Unexpanded leaves Fast shoot growth Not much chlorophyll Helps young shoots quickly reach the surface
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• De-etiololation (greening) is stimulated by light The cessation of etiolation Chlorophyll starts being produced in abundance Shoots slow in growth Leaves unfurl Plant prepares for photosynthesis Plant Hormones • Auxin was the first plant hormone discovered • Auxin transmits a chemical signal downward from the tip of a shoot (coleoptile) to elongating regions • Responsible for “bending” of plant stems during the growth of some plants • Auxin Experiments • Capping the coleoptile stops the bending effect • Screening the coleoptile stops the effect as well • Bysen-Jensen, 1913 • Auxin effect still works when coleoptile signals are added without the coleoptile • Went, 1926 Hormone: Auxin • Produced in embryos, apical meristems, and young leaves • Stimulates • Stem elongation • Root growth • Cell differentiation • Branching • Regulates fruit development • Enhances Apical Dominance • and more… Hormone: Cytokinins • Produced in actively growing tissues • Roots, Embryos and Fruits • Affect root growth and differentiation • Stimulate cell division and plant growth • Stimulate germination • Delay senescence (aging) • Inhibits protein breakdown
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• Control Apical Dominance • Suppresses development of axillary buds • Works with Auxin to control Apical Dominance Hormone: Giberellins
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CH39_summary - Plant Responses to Internal and External...

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