Control Systems in Plants

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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

12
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

18
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