Plant Hormones

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Plant Hormones
2013-04-30 20:17:10
BIO 220

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  1. Plants Respond To The Environment
    • Communication between different parts of plant.
    • -  track time of day and year
    • -  respond to gravity and light
  2. Hormone ( a more general definition)
    A compound produced by one part of an organism that is translocated   to other parts where it triggers a response in target cells and tissues
  3. Phototropism
    growth toward or away from lgith
  4. Experiments on phototropism:
    Charles nad Francis Darwin
    Removed tip of coleoptile from grass seedling (or   covered   with opaque cap) and it failed to grow   toward light.
  5. Experiments on phototropism:
    Peter Boysen-Jensen
    Separated tip from coleoptile by block of gelatin,   preventing cellular contact but allowing chemical   diffusion.
  6. Experiments on phototropism:
    FW Went
    Removed coleoptile tip, placed it on agar block and   then put   agar (without tip) on decapitated coleoptiles   that were kept in dark.
  7. Experiments on phototropism:
    Kenneth Thimann
    • Purified and characterized auxin.
  8. Five Classes Of Plant Hormones Have Been Identified

    • 1.  Auxins (e.g., IAA) 
    •  2.  Cytokinins (e.g., zeatin) 
    •  3.  Gibberellins (e.g., GA3)  
    • 4.  Abscisic acid  
    • 5.  Ethylene
    •   6.  Brassinosteroids
  9. tropism
    Growth responses that result in curvatures of whole   plant organs toward or away from stimuli
  10. Three primary stimuli resulting in tropisms
    • Phototropism - light
    • 2) Gravitropism - gravity
    • 3) Thigmotropism - touch
  11. Phototropism
    • Cells on the dark side of shoot elongate faster, due to asymmetric    distribution of auxins.
    • -  Photoreceptor in shoot tip:  riboflavin related yellow pigment   sensitive to blue light.
    • Auxins move laterally across tip from bright to dark
  12. Gravitropism
    • Orientation of a plant to a field of gravity.
    • -  Roots have positive gravitropism, shoots negative
  13. Mechanisms of Gravitropism
    • Statoliths in root cap cells and in shoot.
    • -  Aggregating statoliths trigger intracellular calcium redistribution and   lateral transport of auxin in root.
    • -  Mechanism in shoots unclear.
  14. Thigmotropism
    • Directional growth in response to touch.
    • -  Contact of tendrils stimulates a coiling response resulting   from differential growth of cells on opposite side.
    •  -  Decrease in length of stem and thickening by mechanical   perturbation. Results from increased ethylene
  15. __ control flowering:
    • Photoperiods 
    • Night length, not day length, determines flowering.
    •   -  Brief exposure to light during night can be disruptive.
    •   -  Leaves detect photoperiod while buds produce flowers.
    •   -  Only one leaf required to detect photoperiod.
  16. Short day plants
    flower late summer, fall, and winter
  17. Long-day plants
    flower late spring and summer
  18. Day-neutral plants
    unaffected by photoperiod
  19. Florigen
    Hypothesized hormone produced by leaves, travels to buds, stimulates   flowering.
  20. Vernalization
    Some plants require cold pretreatment, before they will flower
  21. Phytochrome
    • A protein containing a chromophore (light-absorbing component)   responsible for plant's ability to respond to photoperiod.
    •   -  Red light: 660 nm, most effective at interrupting night length.
    •   -  Far-Red: 730 nm, reverses effect of Red flash.
    •   -  Phytochrome alternates between two forms: Pr and Pfr
    •   -  In darkness Pfr gradually reverts to Pr