control systems in plants. plant hormones l coordinates growth l coordinates development l...
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Control Systems in Plants
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Plant Hormones
Coordinates growth Coordinates development Coordinates responses to
environmental stimuli
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Plant Hormones Auxin (IAA) Cytokinins Gibberllins Abscisic Acid Ethylene Oligogaccharins Brassinosteroids
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Auxins Stimulates stem elongation Stimulates root growth Stimulates differentiation and
branching Stimulates development of fruit Stimulates apical dominance Stimulates phototropism and
gravitropism
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Auxin Control Auxin stimulates
growth Auxin block on right
causes cells to elongate and the plant bends left
Auxin block on left causes cells to elongate the the plant bends right
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Polar Transport Auxin is transported from apex
to shoot Cell wall is acidic
auxin ion picks up H+ diffuses across plasma membrane
Cytosol is neutral auxon loses H+ uses energy to pump out H+ to
maintain pH leaves cell through carrier proteins
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Acid Growth Hypothesis Proton pump stimulated by auxin which lower pH of wall Hydrogen Ion activates Enzyme Enzyme breaks hydrogen bonds in cellulose Wall takes up water and elongates
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Auxin Others Promotes secondary growth by
encouraging vascular cambium and secondary xylem
Promotes adventitious root at the base of a cut stem
Promotes fruit growth without pollination (seedless tomatoes)
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Cytokinins Stimulates root growth Stimulates cell division and
differentiation (with auxins) more cytokinin - shoot buds develop more auxin - roots develop
Stimulates germination Delays Senescence
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Gibberellins Promotes seed and bud germination Promotes stem elongation Promotes leaf growth Stimulates flowering and fruits
(with auxin)
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Abscisic Acid Inhibits growth (with gibberellins) Closes stomata under water stress Permits dormancy
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Ethylene Promotes fruit ripening Controls Abscission
(with auxin)
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Oligosaccharins Triggers defense responses against
pathogens Regulates growth
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Brassinosteroids Required for normal growth and
development
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Signal-Transduction Pathways A hormone binds to receptor and stimulates secondary
messengers which Activates cell responses
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Plant Movements
Phototropism Gravitropism Thigmotropism
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Plant Movement
Rapid Leaf Movement drop in turgor pressure within
pulvini (at joints of the leaf) sent by action potentials
Sleep Movements cells on opposite sides of pulvinus
control the movement
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Daily and Seasonal Responses
Circadian Rhythm Photoperiodism
controls flowering (short-day vs. long-day) critical night length
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Photoperiodic Control
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Flowering Hormones
Experiment indicates the presence of some type of flowering hormone
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Phytochromes Function as photoreceptors / red (660nm) to far red (730nm) Activates kinases (regulatory proteins)
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Red vs. Far Red Response
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Plant Responses to Environmental Stress
Water Deficit Oxygen Deprivation Salt Stress Heat Stress Cold Stress Herbivores
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Water Deficit
Slows Transpiration stomata close release of abscisic acid
Inhibits growth of young leaves Change leaf shape Deeper root growth
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Oxygen Deprivation
Aerial roots Production of air tubes
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Salt Stress
Salt glands Compatible solutes
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Heat Stress
Heat-shock proteins
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Cold Stress
Altering the lipid composition of their membranes
Changes in the solute composition of the cytosol
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Responses to Herbivores Produce
Canavanine Recruitment of
predatory animals
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Defense Against Pathogens Gene-for-gene
recognition
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Defense Against Pathogens Hypersensitive response (HR)
phytoalexins are released PR proteins are released Seal off infected area
Systemic acquired resistance (SAR) Salicylic acid released due to death of cell Activates a Signal Transduction Pathway Activates SAR