auxin - western oregon university
TRANSCRIPT
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Auxin• History• Biochemistry• Transport of Auxin• Physiological action
of Auxin• Mode of action
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History
• 1st hormone discovered
• Darwin's work • Went's work • Phototropism
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Paal & Went
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Biochemistry
• Derived from tryptophan
• Indole 3-acetic acid • weak acid, pk=5 • conjugated IAA • degradation • produced in
meristems
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Conjugation and Degradation
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Transport of Auxin
• basipetal transport from meristems
• evidence for basipetaltransport
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Polar Transport of Auxin
• chemosmoticdiffusion model
• proton pumps lower cell wall pH
• transport proteins at base of cell
• cell pH=7, so IAA-
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PIN1 protein
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Physiological action of Auxin
• Growth in stems and coleoptiles
• Inhibits growth in roots
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Phototropism in coleoptiles
• lateral redistribution of IAA to shaded side
• evidence for this, agar blocks
• type of photoreceptor • blue light, flavin
molecule
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Gravitropism
• statoliths• starch containing
amyloplasts• effect of Ca ions • supra-optimal effect
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Distribution of Auxin
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Physiological effects
• apical dominance • rooting of cuttings • tissue culture • herbicides- synthetic
auxin, agent orange
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Auxin effects
fruit development
•Wounding and xylem regeneration
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Mode of Action
• hormone receptor on membrane
• Short term effects • acid growth
hypothesis • wall loosening • proton pumps • Long term effects • protein synthesis
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Lag time for auxin induced growth
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Auxin induced acidification
• Auxin induces extrusion of H+
• Acidifies the cell wall
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Model for Auxin cell elongation