phytohormones
Post on 16-Dec-2015
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Phytohormones, 1
Phytohormones
HORT 3000
Phytohormones
Naturally occurring organic (C-H-O based) substance that influences physiological processes
Chemical messenger within the plant Provides communication between different areas within the plant Site of action is often different from site of synthesis Six main types in plant
Auxins, Gibberellins, Cytokinins, Abscisic Acid, Ethylene, Brassinosteriods Auxin
Indole-3-acetic acid First hormone to be discovered Ubiquitous throughout the plant Synthesized in embryos and shoots Concentration varies highest in actively growing regions
Stimulates cell elongation Auxin Polar Transport
Preferential movement in one direction Predominately basipetal auxin movement in the shoot auxin moves from morphological
apex towards morphological base
Auxin moves from shoot apex down stem Path of transport not totally clear travels in cells near vascular tissue
Basipetal and acropetal movement occur in roots Basipetal auxin moves away from root tip via epidermal and cortical cells Acropetal auxin moves towards root tip through stele
Auxin Polar Transport
Auxin Polar Transport
Auxin Acid Growth Hypothesis
Auxin-activated proton pump in cell membrane acidifies cell wall space Pumps in protons from cytosol
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Phytohormones, 2
Lower pH activates wall-loosening enzymes, extensins Extensins loosen glycan bonds between microfibrils within cell wall
Turgor then causes micofibrils to be displaced, allowing elongation Auxin Acid Growth Hypothesis
Auxin Vascular Differentiation
IAA-induced xylem regeneration Polar auxin transport visible in accumulation above wound Xylem regeneration occurs first above wound Auxin Root Initiation
Auxin Axillary Bud Break
Auxin Tropic Curvature and Growth
Gibberellins
Gibberellic Acid, GA3 Synthesized in seeds, fruits, and young leaves Modified in roots Stem elongation Flower and fruit development Gibberellins Internode Elongation
Gibberellins Seed Germination
Helps to mobilize endosperm reserves Gibberellins Flower and Fruit Development
Cytokinins
Kinetin Benzyladenine Zeatin Synthesized in root Important for cell division
Cytokinesis division of cytoplasm during mitosis Used in tissue culture to encourage shoot proliferation
(auxin used to promote root proliferation) Cytokinin Witchs Broom
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Phytohormones, 3
Fungal infection causes overproduction of cytokinin and uncontrolled axillary bud development
Abscisic Acid
ABA Synthesized mostly in mature leaves Not actually directly involved in abscission Important signal for plant water relations, stomatal activity Active during seed germination Ethylene
H2C=CH2 (gas) Synthesized
In all plant organs In tissues experiencing stress In tissues experiencing senescence and/or ripening
MCP = ethylene blocker used to preserve cut flowers Methylcyclopropene
Phytohormones
Brassinosteriods
Brassinolide is active component Newly discovered group of hormones Stimulate shoot growth and inhibit root growth Involved in stem elongation and leaf morphogenesis Play a role in vascular differentiation Phytohormones
HORT 3000
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